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"'""■ti'.<.'<:m.m 


A  TEXT-BOOK  OF 


ANIMAL  PHYSIOLOG-T 


WITH  INTRODUCTORY  CHAPTERS 

ON  GENERAL  BIOLOOY 

AND  A  FULL  TREATMENT  OF  REPRODUCTION 


FOR  STUDENTS  OF  HUMAN   AND  COMPARATIVE  (VETERINARY) 
MEDICINE  AND   OF   GENERAL   BIOLOGY 


UY 


WESLEY    MILLS 

M.  A.,  M.  D.,  L.  R.  C.  P.  (ENG.) 


FBOFESSOR  OF  PHYSIOLOGY   IN'   MC  GILL   UNIVERSITY  AND   THE   VETEniNARY  COLLEGE 

MONTREAL 


WITH   OVER   FIVE   HUNDRED   ILLUSTRATIONS 


NEW     Y  O  R K 
D  .    A  P  P  L  E  T  O  N    AND    COMPANY 

LONDON:  CAXTON  HOUSE.  PATERNOSTER  SQUARE 
1889 


/Vl  (9  2 


Copyright,  1889, 
By  D.  APPLETON  AND  COMPANY. 


®o  tl}c  iUcmorn  of 
ROBERT   PALMER   HOWARD,   M.  D.,  LL.  D., 

LATE   DEAN   AMI)   PROFESSOR   OF    MEDICINE   IN    MC  GILL   UNIVERSITY, 

WHOSE  TEACHING  AND  PRACTICE  EVER  TENDED  TOWARDS 

THE    RECOGNITION   OF   THE    IMPORTANCE    OF    PHYSIOLOGY    TO    MEDICINE, 

AND    WHOSE    LIFE    ILLUSTRATED 

WHAT    IS    LOFTY   AND    NOBLE    IN    HUMAN    EXISTENCE, 

THIS  WORK   IS  DEDICATED 
IN    REVERENCE    AND    GRATITUDE. 


PREFACE 


The  comparative  method,  the  introduction  of  the  teach- 
ings of  embryology  and  of  the  welding  principles  of  evolution 
as  part  of  the  essential  structure  of  zoology,  may  be  said  to 
have  completely  revolutionized  that  science ;  and  there  is 
scarcely  a  text-book  treating  of  the  subject,  however  element- 
ary, which  has  not  been  molded  in  accordance  with  these 
guiding  lines  of  thought.  So  far  as  I  am  aware,  this  can 
not  be  said  of  a  single  book  on  the  subject  of  physiology. 
Feeling,  therefore,  that  the  time  had  come  for  the  appearance 
of  a  work  which  should  attempt  to  do,  in  some  degree  at 
least,  for  physiology  what  has  been  so  well  done  for  morphol- 
ogy, the  present  task  was  undertaken.  But  there  were  other 
changes  which  it  seemed  desirable  to  make.  I  tliink  any  one 
who  will  examine  the  methods  and  reasoning  of  the  physi- 
ology of  the  day  will  not  fail,  on  close  scrutiny,  to  recognize 
a  tendency  to  speak  of  certain  conclusions,  for  various  organs 
(and  functions),  as  though  they  applied  to  these  organs  in 
whatever  group  of  animals  found,  or,  at  all  events,  for  man, 
no  matter  what  the  species  of  the  animal  that  liad  been  ex- 
perimented upon.  For  some  years  I  have,  in  publications  of 
my  own  original  researches,  strongly  protested  against  such 
methods  as  illogical.  I  am  wholly  at  a  loss  to  understand 
how  a  work,  built  upon  the  most  fragmentary  and  hetero- 
geneous evidence,  derived  from  experiments  on  a  few  grf)ups 
of  animals,  or  a  certain  amount  of  human  (clinical  or  patho- 
logical evidence,  can  be  fittingly  termed  a  treatise  on  "  human 
j>hy..siology."     It  will  scarcely  bo  denied  that  conclusions  such 


VI 


ANIMAL  PHYSIOLOGY. 


as  this  method  implies  would  not  be  tolerated  in  the  sub'^ect 
of  morphology. 

While  in  the  present  work  what  is  strictly  applicable  to 
other  animals  and  to  man  has  not  always  been  kept  apart, 
an  effort  has  been  made  throughout  to  be  cautious  in  all  the 
conclusions  drawn — a  state  of  mind  warranted  by  the  past 
history  and  the  present  tendencies  of  physiology.  Until  our 
laboratory  methods  become  more  perfected,  the  comparative 
method  more  extensively  applied,  and  conclusions  drawn  from 
"experiments"  modified  by  comparison  with  the  results  of 
clinical,  pathological,  and  all  other  available  sources  of  infor- 
mation, I  feel  convinced  that  we  are  called  upon  to  teach 
cautiously  and  modestly. 

Treating,  as  we  do  in  our  books,  each  subject  in  a  separate 
chapter,  there  is,  as  I  know  by  observation,  the  greatest  danger 
that  the  student  may  get  the  idea  that  each  function  of  the 
body  is  discharged  very  much  independently ;  accordingly, 
there  has  been  throughout  a  most  persistent  effort  made  to 
impress  the  necessity  for  ever  remembering  the  absolute  de- 
pendence of  all  parts.  Unless  this  be  thoroughly  infused 
into  a  student,  it  is  impossible  that  he  can  ever  understand 
the  wide  world  of  natural  objects,  or  the  narrower  one  of  un- 
natural (in  a  sense)  organisms,  as  seen  in  the  hospital  ward. 

Recognizing  how  important  it  is  to  teach  the  young  stu- 
dent to  become  an  observer  and  an  investigator  in  spirit  and 
in  some  degree  in  fact,  only  such  treatment  of  elaborate 
methods  has  been  introduced  as  will  enable  him  to  form  a 
general  acquaintance  with  the  modes  in  which  laboratory 
work  is  carried  on,  while  simple  ways  of  verifying  the  essen- 
tial truths  of  physiology  have  been  constantly  brought  before, 
him.  As  to  how  far  these  are  actually  carried  out  will  de- 
pend not  a  little  on  the  teacher.  The  student  who  learns  thus 
to  observe  and  to  verify  will  not  fail  to  apply  the  method  in 
his  future  career,  whatever  that  may  be — whether  medical  or 
other — nor  is  he  so  likely  to  throw  his  physiology  overboard 
as  a  useless  cargo  as  soon  as  his  primary  examination  has 
been  passed. 


PREFACE.  vii 

By  frequently  calling  attention,  as  has  been  done  tlirongli- 
out,  to  actually  discovered  or  possible  differences  in  function 
for  different  groups  of  animals,  it  is  believed  that  the  student 
will  become  possessed  of  a  spirit  of  caution  in  drawing  con- 
clusions that  will  fit  him  the  better  for  the  hospital  ward  in 
another  respect,  viz.,  that  he  will  be  prepared  for  those  indi- 
vidual differences  actually  existing,  and  which  seem  to  have 
been  largely  ignored  in  so  many  works  on  physiology,  with 
the  natural  consequence  that  the  student,  not  finding  his 
physiology  squaring  with  the  facts  of  the  clinique,  and  not 
being  prepared  for  the  situation,  the  result  is  disappointment 
and  disgust,  instead  of  the  actual  continuation  of  the  study, 
especially  as  human  physiology. 

With  a  view  of  widening  the  student's  field  of  vision,  sec- 
tions, under  the  heading  "  Special  Considerations,"  have  been 
introduced,  which  it  is  hoped  will  not  fail  to  interest  and 
stimulate. 

Most  teachers  of  experience  will  welcome  the  summary 
with  which  each  chapter  concludes.  In  connection  with  no 
subject  perhaps  can  the  art  of  generalizing  be  better  taught 
than  with  physiology,  and  to  this  end  these  brief  synoptical 
sections  will,  it  is  thought,  prove  helpful. 

Systematic  instruction  in  either  macroscopic  or  microscopic 
anatomy  has  not  been  undertaken — in  fact,  can  not  be  at- 
tempted, it  is  believed,  except  at  the  expense  of  physiology 
proper — in  a  work  of  moderate  compass.  At  the  same  time 
attention  has  been  called  to  those  points  which  have  a  special 
bearing  on  each  function,  and  a  number  of  illustrations  have 
been  inserted  with  this  object  in  view. 

The  introduction  of  the  subject  of  development  at  so  early 
a  stage  is  a  departure  that  calls  for  a  word  of  explanation. 
An  attempt  has  been  made  to  use  embryological  facts  to 
throw  light  upon  the  different  functions  of  the  body,  and 
especially  their  relations  and  interdependence.  It  therefore 
became  necessary  to  treat  the  subject  early.  It  is  expected, 
however,  that  the  student  will  return  to  it  after  reading  the 
remaining  chapters  of  the  woik. 


yiii  ANIMAL  PHYSIOLOGY. 

As  so  large  a  proportion  of  those  who  enter  upon  the 
study  of  medicine  begin  their  career  without  any  adequate 
preparation  in  general  biology,  the  subject,  as  presented  in 
this  work,  will,  let  me  hope,  meet  an  actual  need,  and  prove 
helpful  in  attaining  a  broad  and  sound  view  of  the  special 
doctrines  of  biology. 

It  is  scarcely  necessary  to  remark  that  clinical  and  path- 
ological facts  have  not  been  introduced  with  the  view  of 
teaching  either  clinical  medicine  or  pathology,  but  to  indi- 
cate to  the  student  how  his  physiology  bears  on  his  profes- 
sion, and  how  the  above-mentioned  subjects  throw  light  upon 
physiology  proper  and  lend  interest  to  that  subject. 

My  aim  has  been  to  make  the  book,  from  first  to  last, 
educative ;  and,  retaining  a  vivid  recollection  of  the  severe 
strain  put  upon  the  memory  of  the  medical  student  by  our 
present  method  of  crowding  so  much  into  at  most  four  years 
of  study,  an  attempt  has  been  made  to  avoid  overloading  the 
book  with  mere  facts  or  technical  details,  as  well  as  to  pre- 
sent the  whole  subject  in  as  succinct  a  form  as  is  compatible 
with  clearness.  Recognizing,  too,  the  very  shifting  character 
of  physiological  theories,  the  latter  have  generally  been  pretty 
well  kept  apart  from  the  actual  facts. 

It  is  hoped  that  the  abundance  of  the  illustrations  will 
prove  more  acceptable  than  would  lengthy  treatment  of  sub- 
jects in  the  text,  for,  if  the  matter  of  a  book  is  to  be  digested 
and  assimilated,  either  by  the  student  of  general  biology  or 
by  the  hard-worked  medical  student,  it  must  not  be  bulky. 

The  illustrations  have  been  chosen  from  the  best  available 
sources,  and  the  authorship  of  each  one  duly  acknowledged 
in  the  body  of  the  work.  Several  original  diagrams,  such  as 
I  find  exceedingly  useful  in  my  own  lectures,  have  been  in- 
troduced. 

This  book  is  really  an  embodiment  of  my  own  course  of 
lectures,  as  given  during  the  past  two  years  more  especially, 
and  with  the  highest  satisfaction,  I  think  it  may  be  said,  to 
both  students  an.d  teacher. 

I  have  unbounded  confidence  in  the  plan  of  the  work,  and 


PREFACE.  ,  ix 

I  ti'ust  that  its  newness  may  excuse,  to  some  degree,  any 
shortcomings  in  the  execution.  Such  a  book  has  become  a 
necessity  to  myself,  and  it  is  hoped  will  be  welcomed  by 
others.  I  trust  the  work  may  prove  suitable,  not  only  for 
the  student  of  luiman  medicine,  but  for  the  increasing  num- 
ber of  students  of  comparative  or  veterinary  medicine,  who 
may  desire  a  broad  basis  for  the  study  of  disease  in  the 
various  animals  they  are  called  upon  to  treat.  I  have  en- 
deavored to  make  the  work  specially  acceptable  to  the  stu- 
dent of  general  biology. 

It  only  remains  for  me  to  crave  the  indulgence  of  all 
readers,  and  to  thank  my  publishers,  Messrs.  D.  Appleton  & 
Co.,  for  their  uniform  courtesy  and  the  great  pains  they  have 
taken  to  present  the  work  in  worthy  form. 

Wesley  Mills. 

Physiological  Laboratory,  McGill  University', 
Montreal,  September,  18S9. 


CONTENTS. 


PAGE 

General  Biology     1 

Introduction 1 

Tabular  statement  of  the  subdivisions  of  Biology          ....  4 

The  Cell 5 

Animal  and  vegetable  cells 5 

Structure  of  cells 5 

Cell-contents 7 

The  nucleus 7 

Tissues 8 

Summary 8 

Unicellular  Or(;anisms  (Vegetable) 9 

1.  Yeast 9 

Morphological 9 

Chemical 10 

Physiological 10 

Conclusions 10 

2.  Protococcus 11 

Morphological 11 

Physiological 11 

Conclusions 13 

Unicellular  Animals 13 

The  proteus  animalcule 13 

Morphological 13 

Physiological 13 

Conclusions 14 

Parasitic  Organisms 15 

Fungi 15 

Miicor  niucodi) 1<> 

The  Bacteria 18 

Unkellular  Animals  with  Differentiation  of  Structure     ...  20 

The  Ijcil-animalcule 30 

Structure -0 

P^unctions 31 

Multicellular  Organisms 33 

The  fresh-water  polyps  , 33 

The  (Jell  reconsioerko 36 

The  Animal  Body — an  epitomized  account  of  the  fmictions  of  u  mainrnal    .  27 


I 

^ii  ANIMAL   PHYSIOLOGY. 

PAGE 

Living  and  Lifeless  Matter— General   explanation  and  comparison   of 

their  properties °l 

Classification  of  the  Animal  Kingdom .  33 

Tabular  statement 35 

Man's  place  in  the  animal  kingdom 35 

The  Law  op  Periodicity  or  Rhythm  in  Nature— Explanations  and  illus- 
trations         36 

The  Law  of  Habit 40 

Its  foundation 40 

Instincts '■      .  •        •        •         .41 

The  Origin  of  the  Forms  of  Life 41 

Arguments  from : 

Morphology     .        .        .    ' 43 

Embryology •         .43 

Mimicry 43 

Rudimentary  organs 43 

Geographical  distribution 45 

Paleontology 45 

Fossil  and  existing  species      .        .        .        , 45 

Progression 46 

Domesticated  animals     .        . 46 

Summary 47 

Reproduction .        .        .50 

General 50 

The  ovum 54 

The  origin  and  development  of  the  ovum 57 

Changes  in  the  ovum  itself 59 

The  male  cell .60 

The  origin  of  the  spermatozoon 61 

Fertilization  of  the  ovum 63 

Segmentation  and  subsequent  changes .  63 

The  gastrula 66 

The  hen's  egg 67 

The  origin  of  the  fowl's  egg •  .        .         .68 

Embryonic  membranes  of  birds     .        . 72 

The  fcetal  (embryonic)  membranes  of  mammals 76 

The  placenta 80 

The  discoidal  placenta 81 

The  metadiscoidal  placenta 81 

The  zonary  placenta 86 

The  diffuse  placenta 86 

The  polycotyledonary  placenta .        .86 

Microscopic  structure  of  the  placenta 87 

Illustrations 87 

Evolution 89 

Summary 89 

The  Development  of  the  Embryo  Itself 90 

Germ-layers 92 

Origin  of  the  vascular  system .97 

The  growth  of  the  embryo 102 


CONTENTS. 


XUl 


ASONING 


Development  of  the  Vascular  System  ix  Vertebrates 

The  later  stages  of  the  foetal  circulation 

Development  of  the  Urogenital  System    . 

The  Physiological  Aspects  of  Development 

Menstruation  and  ovulation  .... 

The  nutrition  of  the  ovum     .... 

The  fffital  circulation      .... 

Parturition 

Changes  in  the  circulation  at  birth 

Sexual  coitus 

Organic  Evolution  reconsidered  . 

Different  theories  criticised — new  views 
The  Chemical  Constitution  of  the  Animal  Body 
Proximate  principles      .         .         .         .         , 
General  characters  of  protcids 
Certain  non-crystalline  bodies 

The  fats 

Peculiar  fats 

Carbohydrates 

Nitrogenous  metabolites .         .        .        , 

Non-nitrogenous  metabolites . 
Physiological  Research  and  Physiological  Re. 
The  Blood 

Comparative  • 

Corpuscles 

History  of  the  blood-cells       .... 

Chemical  composition  of  the  blood 

Composition  of  serum     .... 

Composition  of  the  corpuscles 

The  quantity  and  distribution  of  the  blood 

The  coagulation  of  the  blood  . 

Clinical  and  pathological 

Summary 

The  Contractile  Tissues        .... 

General 

Comparative 

Ciliary  mr)vements 

The  irritability  of  muscle  and  nerve 
Applications  of  the   Graphic  Method  to  the 
Physiology 

Chronographs  and  various  kinds  of  apparatus 
A  single  muscular  contraction 
Tetanic  contraction 

The  muscle-tone 

The  strength  of  the  stimulus. 
The  changes  in  a  muscle  during  contraction 
The  elasticity  of  muscle         .... 

The  eloctrical  phenomena  of  muscle 

Chemical  changes  in  muscle    . 
Thermal  changes  in  tlie  contracting  muscle . 


Study  of 


Muscle 


171 


PAGE 

103 
103 
106 
113 
113 
115 
118 
120 
120 
131 
127 
137 
135 
137 
138 
138 
139 
140 
140 
140 
141 
141 
147 
148 
149 
151 
154 
155 
155 
156 
157 
163 
165 
166 
166 
167 
168 
169 

171 
-174 
178 
183 
184 
185 
186 
187 
188 
193 
195 


XIV 


ANIMAL  PHYSIOLOGY. 


PAaE 

The  physiology  of  nerve ' 196 

Eleetrotonus •  196 

Pathological  and  clinical 198 

Law  of  contraction 198 

Electrical  organs 199 

Muscular  work 199 

Circumstances  influencing  the  character  of  muscular  and  nervous  activity  200 

The  influence  of  blood-supply  and  fatigue 200 

Separation  of  muscle  from  the  central  nervous  system ....  202 

The  influence  of  temperature 202 

The  intimate  nature  of  muscular  and  nervous  action    .         .         .         .  203 

Unstriped  muscle 204 

General 204 

Comparative 205 

Special  considerations 205 

Functional  variations 207 

Summary  of  the  physiology  of  muscle  and  nerve 208 

The  Nervous  System — General  Considerations 210 

Experimental 212 

Automatism 214 

Conclusions 214 

Nervous  inhibition 215 

The  Circulation  of  the  Blood .  216 

General 216 

The  mammalian  heart 217 

Circulation  in  the  mammal 221 

The  action  of  the  mammalian  heart 223 

The  velocity  of  the  blood  and  blood-pressure 224 

General 224 

Comparative ■ 225 

The  circulation  under  the  microscope 226 

The  characters  of  the  blood-flow 227 

Blood-pressure 228 

The  Heart '.        .  232 

The  cardiac  movements 232 

The  impulse  of  the  heart .  233 

Investigation  of  the  heart-beat  from  within 234 

The  cardiac  sounds 235 

Causes  of  the  sounds 236 

Endo-cardiac  pressures 238 

The  worlf  of  the  heart    ... 241 

Variations  in  the  cardiac  pulsation 242 

The  pulse 244 

Features  of  an  arterial  pulse-tracing 247 

Venous  pulse 251 

Pathological 251 

Comparative 251 

The  beat  of  the  heart  and  its  modifications 261 

The  nervous  system  in  relation  to  the  heart 261 

Influence  of  the  vagus  nerve  on  the  heart 265 


CONTEXTS.  XV 

PAGE 

Conclusions      .        .      ' 269 

The  accelerator  nerves  of  the  heart 270 

Human  physiology 273 

The  heart  in  relation  to  blood-pressure 274 

The  influence  of  the  quantity  of  blood 275 

Conclusions 277 

The  capillaries 281 

Special  considerations 282 

Pathological 282 

Personal  observations 283 

Comparative 283 

Evolution 285 

Summary  of  the  physiology  of  the  circulation 286 

DiGESTiox  OF  Food 290 

Foodstufls.  milk,  etc 290 

Embryologieal 295 

Comparative 296 

The  digestive  juices 306 

Saliva  and  its  action 306 

Secretion  of  the  different  glands 307 

Comparative 308 

Pathological 308 

Gastric  juice 308 

Bile         . 311 

General 311 

Pigments 312 

Digestive  action 313 

Comparative 314 

Pancreatic  secretion 314 

Succus  entericus 317 

Comparative 319 

Secretion  as  a  physiological  process 319 

Secretion  of  the  salivary  glands 319 

Secretion  by  the  stomach 323 

The  secretion  of  bile  and  pancreatic  juice 323 

The  nature  of  the  act  of  secretion 326 

Self-digestion  of  the  digestive  organs 329 

Comparative 330 

The  movements  of  the  digestive  organs 331 

Deglutition '     -        .  332 

CVtmparative 335 

The  movements  of  the  stomach 335 

Comparative 336 

Pathological 336 

The  intestinal  movements 337 

Defecation 337 

Vomiting 338 

Com[)arative 339 

Pathological 339 

The  removal  of  digestive  jjroducts  from  the  alimentary  canal     .        .        .  341 

B 


^^  ANIMAL   PHYSIOLOGY. 


PAGE 


Lymph  and  chyle ^'*^ 

The  movements  of  the  lymph— comparative          .        .        .        .        .342 
Pathological ^^^ 


Fseces 


353 


Pathological ^^4 

The  changes  produced  in  the  food  in  the  alimentary  canal .         ...  355 

General ^^^ 

Comparative 357 

Pathological 357 

Special  considerations 358 

Various 358 

Human  physiology 363 

Evolution 363 

Summary •  364 

The  Respiratory  System 365 

General 365 

Anatomical 368 

The  entrance  and  exit  of  air 369 

The  muscles  of  respiration 372 

Types  of  respiration 373 

Personal  observation 374 

Comparative .  375 

The  quantity  of  air  respired 378 

The  respiratory  rhythm 379 

General 379 

Pathological 379 

Respiratory  sounds 381 

Comparison  of  the  inspired  and  the  expired  air 381 

Respiration  in  the  blood 383 

Haemoglobin  and  its  derivatives 385 

General 385 

Blood-spectra 387 

Comparative 389 

The  nitrogen  and  the  carbon  dioxide  of  the  blood         ....  389 

Foreign  gases  and  respiration 392 

Respiration  in  the  tissues 392 

The  nervous  system  in  relation  to  respiration 393 

Nerves  and  centers  concerned 395 

The  influence  of  the  condition  of  the  blood  on  respiration   .         .        .  397 

The  Cheyne-Stokes  respiration 398 

The  effects  of  variations  on  the  atmospheric  pressure 399 

The  influence  of  respiration  on  the  circulation 400 

General 400 

Comparative 402 

The  respiration  and  circulation  in  asphyxia 404 

Pathological ' 406 

Peculiar  respiratory  movements 406 

Coughing,  laughing,  etc 406 

Comparative 407 

Special  considerations 408 


CONTENTS.                                     '  xvii 

PAGE 

Pathological  and  chemical 408 

Personal  observation 408 

Evolution 409 

Summary  of  the  physiology  of  respiration 410 

Protective  and  Excretory  Functions  op  the  Skin 412 

General 412 

Comparative 413 

The  excretory  function  of  the  skin 415 

Normal  sweat 415 

Pathological 415 

Comparative — Respiration  by  the  skin 415 

Death  from  suppression  of  the  functions  of  the  skin     ....  416 

The  excretion  of  perspiration 416 

Experimental 416 

Human  physiology 417 

Absorption  by  the  skin 418 

Comparative 418 

Summary 418 

Excretion  by  the  Kidney 419 

Anatomical 419 

Comparative 419 

Urine  considered  physically  and  chemically 422 

Specific  gravity 422 

Color 423 

Reaction 423 

Quantity 423 

Composition  :  Nitrogenous  crystalline  bodies 423 

Non-nitrogenous  organic  bodies 424 

Inorganic  salts 424 

Abnormal  urine 425 

Comparative 425 

The  secretion  of  urine 426 

Methods  of  investigation 426 

Theories  of  secretion 427 

Nervous  influence 428 

Pathological 428 

The  expulsion  of  tirine 429 

General 429 

Facts  of  exitcrimont  and  of  experience  .....••  429 

Pathological 430 

Comparative 430 

Summary  of  urine  and  the  functions  of  the  kidneys 430 

TiiK  Metabolism  ok  the  Body 431 

(ieneral  remarks 431 

The  metabolism  of  the  liver 4.'}2 

The  glycogenic  function 44^2 

The  uses  of  glycogen 434 

Pathological 435 

Metabolism  of  the  spleen 436 

Histological 436 


XVlll 


ANIMAL  PHYSIOLOGY. 


PAGE 

Chemical 437 

Spleen  curves 439 

The  nervous  system  in  relation  to  the  spleen         .         .         .        .         .  439 

The  construction  of  fat 440 

General  and  experimental 440 

Histological 441 

Changes  in  the  cells  of  the  mammary  gland  .         .         .         .         .         .  443 

Milk  and  colostrum 448 

Nature  of  fat-formation 444 

Pathological 445 

Comparative 445 

The  metabolic  processes  concerned  in  the  formation  of  urea,  uric  acid, 

hippuric  acid,  and  allied  bodies 446 

General  discussion 446 

Pathological 448 

Evolution 448 

The  study  of  the  metabolic  processes  by  other  methods       ....  449 

Various  tabular  statements •.         .         .        .  450 

Starvation  and  its  lessons        .........  450 

Comparative 453 

Diets .        .453 

Feeding  experiments 454 

General 454 

Proteid  metabolism 455 

Nitrogenous  equilibrium 456 

Comparative 456 

The  effects  of  gelatine  in  the  diet .  457 

Fat  and  carbohydrates 457 

Comparative 458 

The  effects  of  salts,  water,  etc.,  on  the  diet 458 

Pathological 459 

The  energy  of  the  animal  body ,         .         .  459 

Tabular  statements .  460 

The  sources  of  muscular  energy 461 

Animal  heat ,  461 

General 461 

Comparative 461 

The  regulation  of  temperature .        .  464 

Cold-blooded  and  warm-blooded  animals  compared       ....  465 

Theories  of  heat  formation  and  heat  regulation 466 

Pathological 467 

Special  considerations ,        ,        ,  467 

Evolution 468 

Hibernation 470 

Daily  variations  in  temperature  in  man  and  other  mammals       .        .  470 

The  influence  of  the  nervous  system  on  metabolism  (nutrition)  .         .         .  471 

Experimental  facts 471 

Discussion  of  their  significance 473 

General  considerations,  chemical  and  pathological        ....  476 

Summary  of  metabolism 476 


CONTEXTS. 


XIX 


PAGE 

The  Spixal  Cord — General 480 

General 480 

Anatomical 482 

The  reflex  functions  of  the  spinal  cord 484 

General  and  experimental 484 

Evolution  and  heredity 485 

Inhibition  of  reflexes 485 

Reflex  time 480 

The  spinal  cord  as  a  conductor  of  imjjulses 487 

Anatomical 488 

Decussation 489 

Pcthological 490 

Paths  of  impulses 491 

The  automatic  functions  of  the  spinal  cord 493 

General 493 

Spinal  phenomena 493 

Special  considerations 495 

Comparative 495 

Evolution 49G 

Synoptical 497 

The  Braix 498 

General  and  anatomical 498 

Animals  deprived  of  their  cerebrum 500 

Behavior  of  various  animals  and  its  significance 500 

Have  the  semicircular  canals  a  co-ordinary  function  ?          .         .        .         .  502 

Experimental,  etc 502 

Discussion  of  the  phenomena          ........  502 

Forced  movements 503 

Functions  of  the  cerebral  convolutions 504 

Comparative 505 

Individual  differences  in  brains      .         .         .        .         .        .         .    ■     .  518 

The  connection  of  one  part  of  the  brain  with  another  ....  518 

The  cerebral  cortex 521 

Theories  of  different  observers 522 

The  circulation  in  the  brain 525 

Sleep — hibernation — dreaming 52G 

Hypnotism — catalepsy — somnambulism 528 

Pathological 530 

Cerebral  localization  reconsidered 530 

Illustrations  of  localization 535 

Different  methods  criticised 535 

Cerebral  time 535 

Functions  of  other  portions  of  the  brain 53G 

The  corpus  striatum  and  the  optic  thalamus 536 

Corpora  quadrigeniina 539 

The  cerebelbim 541 

Pathological 541 

Crura  cerebri  and  and  jjons  Varolii 541 

PallH.Iogical 542 

iMedulla  ol>lon„'ata 542 


XX  ANIMAL  PHYSIOLOGY. 

PAGE 

Special  considerations    . ^43 

Embryologieal         .        .        .        .        •        •        •        ...        .        •  542 

Evolution 543 

Synoptical 547 

General  Remarks  on  the  Senses 548 

Anatomical 548 

General  principles 550 

The  Skin  as  an  Organ  of  Sense 551 

General 551 

Pathological 553 

Pressure  sensations 554 

Thermal  sensations 554 

Tactile  sensibility 555 

The  muscular  sense 557 

General 557 

Pathological 557 

Comparative 558 

Synoptical 559 

Vision 559 

Physical 559 

Anatomical 561 

Embryologieal 562 

Dioptrics  of  vision 563 

Accommodation  of  the  eye 563 

Alterations  in  the  size  of  the  pupil 569 

Phenomena  and  their  explanations 570 

Pathological 572 

Optical  imperfections  of  the  eye 572 

Spherical  aberration 572 

Astigmatism 573 

Chromatic  aberration 573 

Entoptic  phenomena 574 

Anomalies  of  refraction 574 

Visual  sensations 576 

General 576 

Affections  of  the  retina 578 

The  nature  of  the  processes  which  originate  visual  impulses        .        .  580 

The  laws  of  retinal  stimulation 581 

The  visual  angle 582 

Color  sensations 583 

Theories  of  color- vision 584 

Color-blindness 585 

Psychological  aspects  of  vision 586 

The  visual  field 586 

Imperfections  of  visual  perceptions  as  "  irradiation,"  etc.     .        .        .  587 

Influence  of  the  pigment  of  the  macula  lutea 589 

After-images,  etc 589 

Misconceptions  as  to  the  comparative  size  of  objects    ....  590 

Subjective  phenomena 591 

Co-ordination  of  the  two  eyes  in  vision 591 


CONTENTS.  xxi 

PAGE 

The  visual  axes 591 

Ocular  movements 592 

The  horopter 594 

Estimation  of  the  size  and  distance  of  objects 595 

Solidity 595 

Protective  mechanisms  of  the  eye 596 

Special  considerations 598 

Comparative 597 

Evolution 600 

Pathological 602 

Brief  synopsis  of  the  physiology  of  vision 602 

Hearing 604 

General 604 

Anatomical 605 

The  membrana  tympani 606 

The  auditory  ossicles 607 

Muscles  of  the  middle  ear 608 

The  Eustachian  tube 609 

Pathological 609 

Auditory  impulses 610 

Auditory  sensations,  perceptions,  judgments 615 

General 615 

Auditory  judgment 615 

Range  of  auditory  discrimination 616 

Special  considerations 616 

Comparative 616 

Evolution 618 

Synopsis  of  the  physiology  of  hearing 620 

The  Sense  of  Smell i        .        .  620 

Anatomical 620 

General 631 

Comparative 622 

The  Sense  of  Taste 623 

Anatomical 623 

General 623 

Experimental 623 

Pathological 625 

Comparative 626 

The  Cerebro-Spinal  System  of  Nerves 626 

1.  Spinal  nerves 626 

General 626 

Exception 627 

Additional  experiments 627 

Pathological 627 

2.  The  cranial  nerves 628 

General 628 

The  motor-oculi,  or  third  nerve 628 

The  trochlear,  or  fourth  nerve 629 

The  al)diicenH,  or  sixth  nerve 629 

The  facial,  or  seventh  nerve    .        .        .         . 629 


XXll 


ANIMAL   PHYSIOLOGY. 


PAGE 

The  trigeminus,  or  fifth  nerve 630 

The  glosso-pharyngeal,  or  ninth  nerve  .         .         .        .         .        •         .  633 

The  pneumogastric,  or  tenth  nerve 633 

The  spinal  accessory,  or  eleventh  nerve 685 

The  hypoglossal,  or  twelfth  nerve 635 

Relations  of  the  cerebro-spinal  and  sympathetic  systems     ....  636 

Eecent  views  on  this  subject  .        . 636 

The  Voice  and  Speech 639 

Physical 639 

Anatomical 640 

Laryngoscopic  observations 643 

Voice-formation 643 

The  registers  and  the  falsetto-voice        .,.,....  644 

Pathological 646 

Comparative 647 

Speech 649 

General 649 

Formation  of  vowels  and  consonants 650 

Whispering 650 

Classification  of  consonants 651 

Pathological    . .         .         .651 

Special  considerations 652 

Evolution 652 

Summary 653 

Locomotion 655 

Anatomical 655 

Mechanical 655 

Standing 656 

Walking 657 

Running 659 

Jumping 659 

Hopping 659 

Comparative :  the  gait  of  quadrupeds    .         .         .         .         .         .         .  659 

Evolution 662 

Man   considered    physiologically   at   the    Different  Periods    of    his 

Existence 663 

Size  and  growth 663 

Digestive  system 664 

Circulatory  and  respiratory  systems 664 

Dentition 665 

Nervous  system 666 

Puberty 666 

The  sexes 667 

Old  age 667 

Comparative 668 

Death 668 

Appendix  :   Animal  Chemistry       . " 671 

Index .        .  691 


AKIMAL  PHYSIOLOGY. 


GENEEAL  BIOLOGY. 
Introduction. 

Biology  {/3lo<;,  life ;  koyos,  a  dissertation)  is  the  science 
which  treats  of  the  nature  of  living  things;  and,  since  the 
properties  of  plants  and  animals  can  not  be  explained  without 
some  knowledge  of  their  form,  this  science  includes  morphol- 
ogy {txop(f>r],  form ;  Aoyos,  a  dissertation)  as  well  as  physiology 
(^uo-is,  nature  ;  Aoyos). 

Morphology  describes  the  various  forms  of  living  things 
and  their  parts ;  physiology,  their  action  or  function. 

General  biology  treats  neither  of  animals  nor  plants  exclu- 
sively. Its  province  is  neither  zoology  nor  botany ;  but  it  at- 
tempts to  define  what  is  common  to  all  living  things.  Its  aim 
is  to  determine  the  properties  of  organic  beings  as  such,  rather 
than  to  classify  or  to  give  an  exhaustive  account  of  either  ani- 
mals or  plants.  Manifestly,  before  this  can  be  done,  living 
things,  both  animal  and  vegetable,  must  be  carefully  compared, 
otherwise  it  would  be  impossible  to  recognize  differences  and 
resemblances ;  in  other  words,  to  ascertain  what  they  have  in 
common. 

When  only  the  highest  animals  and  plants  are  contem- 
plated, the  differences  between  them  seem  so  vast  that  they 
appear  to  have,  at  first  sight,  nothing  in  common  but  that  they 
are  living :  between  a  tree  and  a  dog  an  infant  can  discrimi- 
nate; but  there  are  microscopic  forms  of  life  that  thus  far 
defy  the  most  learned  to  say  whether  they  belong  to  the  ani- 
mal or  tlie  vegetable  world.  As  we  descend  in  the  organic 
series,  the  lines  of  distinction  grow  fainter,  till  they  seem 
finally  to  all  but  disappear. 

But  let  us  first  inciuire :  What  are  the  determining  charac- 
1 


2  ANIMAL  PHYSIOLOGY. 

teristics  of  living  things  as  sucli  ?  By  what  barriers  are  the 
animate  and  inanimate  worlds  separated?  To  decide  this, 
falls  within  the  province  of  general  biology. 

Living  things  grow  by  interstitial  additions  of  particles  of 
matter  derived  from  without  and  transformed  into  their  own 
substance,  while  inanimate  bodies  increase  in  size  by  superfi- 
cial additions  of  matter  over  which  they  have  no  power  of 
decomposition  and  recomposition  so  as  to  make  them  like 
themselves.  Among  lifeless  objects,  crystals  approach  near- 
est to  living  forms ;  but  the  crystal  builds  itself  up  only  from 
material  in  solution  of  the  same  chemical  composition  as  itself. 

The  chemical  constitution  of  living  objects  is  peculiar.  Car- 
bon, hydrogen,  oxygen,  and  nitrogen  are  combined  into  a  very 
complex  whole  or  molecule,  as  protein;  and,  when  in  com- 
bination with  a  large  proportion  of  water,  constitute  the  basis 
of  all  life,  animal  and  vegetable,  known  as  protoplasm.  Only 
living  things  can  manufacture  this  substance,  or  even  protein. 

Again,  in  the  very  nature  of  the  case,  protoplasm  is  con- 
tinually wasting  by  a  process  of  oxidation,  and  being  built  up 
from  simpler  chemical  forms.  Carbon  dioxide  is  an  invariable 
product  of  this  waste  and  oxidation,  while  the  rest  of  the  car- 
bon, the  hydrogen,  oxygen,  and  nitrogen  are  given  back  to  the 
inorganic  kingdom  in  simpler  forms  of  combination  than  those 
in  which  they  exist  in  living  beings.  It  will  thus  be  evident 
that,  while  the  flame  of  life  continues  to  burn,  there  is  constant 
chemical  and  physical  change.  Matter  is  being  continuously 
taken  from  the  world  of  things  that  are  without  life,  trans- 
formed into  living  things,  and  then  after  a  brief  existence  in 
that  form  returned  to  the  source  from  which  they  were  origi- 
nally derived.  It  is  true,  all  animals  require  their  food  in  or- 
ganized form — that  is,  they  either  feed  on  animal  or  plant 
forms ;  but  the  latter  derive  their  nourishment  from  the  soil 
and  the  atmosphere,  so  that  the  above  statement  is  a  scientific 
truth. 

Another  highly  characteristic  property  of  all  living  things 
is  to  be  sought  in  their  periodic  changes  and  very  limited  dura- 
tion. Every  animal  and  plant,  no  matter  what  its  rank  in  the 
scale  of  existence,  begins  in  a  simple  form,  passes  through  a 
series  of  changes  of  varying  degrees  of  complexity,  and  finally 
declines  and  dies ;  which  simply  means  that  it  rejoins  the  in- 
animate kingdom:  it  passes  into  another  world  to  which  it 
formerly  belonged. 

Living  things  alone  give  rise  to  living  things ;  protoplasm 


GENERAL  BIOLOGY.  3 

alone  can  beget  protoplasm ;  cell  begets  cell.  Omne  aniTnal 
{anima,  lite)  ex  ovo  applies  with  a  wide  interpretation  to  all 
living  forms. 

From  what  has  been  said  it  will  appear  that  life  is  a  condi- 
tion of  ceaseless  change.  Many  of  the  movements  of  the  pro- 
toplasm composing  the  cell-units  of  which  living  beings  are 
made  are  visible  under  the  microscope ;  their  united  effects  are 
open  to  common  observation — as,  for  example,  in  the  move- 
ments of  animals  giving  rise  to  locomotion  we  have  the  joint 
result  of  the  movements  of  the  protoplasm  composing  millions 
of  muscle-cells.  But,  beyond  the  powers  of  any  microscope  that 
has  been  or  probably  ever  will  be  invented,  there  are  molecular 
movements,  ceaseless  as  the  flow  of  time  itself.  All  the  processes 
which  make  up  the  life-history  of  organisms  involve  this  mo- 
lecular motion.  The  ebb  and  flow  of  the  tide  may  symbolize 
the  influx  and  efflux  of  the  things  that  belong  to  the  inanimate 
world,  into  and  out  of  the  things  that  live. 

It  follows  from  this  essential  instability  in  living  forms  that 
life  must  involve  a  constant  struggle  against  forces  that  tend 
to  destroy  it ;  at  best  this  contest  is  maintained  successfully  for 
but  a  few  years  in  all  the  highest  grades  of  being.  So  long  as 
a  certain  equilibrium  can  be  maintained,  so  long  may  life  con- 
tinue and  no  longer. 

.  The  truths  stated  above  will  be  illustrated  in  the  simpler 
forms  of  plants  and  animals  in  the  ensuing  pages,  and  will  be- 
come clearer  as  each  chapter  of  this  work  is  perused.  They 
form  the  fundamental  laws  of  general  biology,  and  may  be 
formulated  as  follows : 

1.  Living  matter  or  protoplasm  is  characterized  by  its  chem- 
ical composition,  being  made  up  of  carbon,  hydrogen,  oxygen, 
and  nitrogen,  arranged  into  a  very  complex  molecule. 

2.  Its  universal  and  constant  waste  and  its  repair  by  inter- 
stitial formation  of  new  matter  similar  to  the  old. 

3.  Its  power  to  give  rise  to  new  forms  similar  to  the  parent 
ones  by  a  process  of  division. 

4.  Its  manifestation  of  periodic  changes  constituting  devel- 
opment, decay,  and  death. 

Though  there  is  little  in  relation  to  living  beings  which 
may  not  be  appropriately  set  down  under  zoology  or  botany,  it 
tends  to  breadth  to  have  a  science  of  general  biology  which 
deals  with  the  properties  of  things  simply  as  living,  irrespective 
very  much  as  to  whether  they  belong  to  the  realm  of  animals 
or  plants.     The  relation  of  the  sciences  wlii(;h  may  be  regarded 


ANIMAL  PHYSIOLOGY. 


as  subdivisions  of  general  biology  is  well  shown  in  the  follow- 
ing table :  * 

Anatomy.  ^ 

The  science  of  structure ;  the 
term  being  usually  ap- 
plied to  the  coarser  and 
more  obvious  composition 
of  plants  or  animals. 

Histology. 
Microscopical  anatomy. 
The  ultimate  optical  an- 
alysis of  structure  by  the 
aid  of  the  microscope ; 
separated  from  anatordy 
only  as  a  matter  of  con- 


Biol- 
ogy. 

The 
science 
of  liv- 
ing 
things ; 
i.  e.,  of 
matter 
in  the 
living 
state. 


Mor- 
phol- 
ogy. 

The 
science 

of 
form, 
struct- 
ure, 
etc. 
Essen- 
tially 
statical. 


Physi- 
ology. 

The 
science 

of 
action 

or 
func- 
tion. 
Essen- 
tially 
dynam- 
ical. 


Taxonomy. 
The  classification  of  living 
things,   based   chiefly  on 
phenomena  of  structure. 

Distribution. 

Considers  the  position  of  liv- 
ing things  in  space  and 
time  ;  their  distribution 
over  the  present  face  of 
the  earth ;  and  their  distri- 
bution and  succession  at 
former  periods,  as  dis- 
played in  fossil  remains. 

Embryology. 
The  science  of  development 
from  the  germ;  includes 
many  mixed  problems 
pertaining  both  to  mor- 
phology and  physiology. 
At  present  largely  mor- 
phological. 

Physiology. 
The  special  science  of  the 
functions  of  the  individ- 
ual in  health  and  in  dis- 
ease ;  hence  including 
Pathology. 

Psychology. 
The  science  of  mental  phe- 
nomena. 

Sociology. 
The   science  of  social  life, 
i.  e.,  the  life  of  communi- 
ties, whether  of   men  or 
of  lower  animals. 


Botany. 

The 
science 
of  veg- 
etal 
living 
matter 

or 
plants. 


Zool- 
ogy. 

The 
science 

of 
animal 
living 
matter 
or  ani- 
mals. 


Biol- 
ogy. 

The 
science 
of  liv- 
ing 
things ; 
i.  e.,  of 
matter 
in  the 
living 
state. 


*  Taken  from  the  *'  General  Biology  "  of  Sedgwick  and  Wilson. 


THE   CELL.  5 

THE    CELL.* 

All  living  things,  great  and  small,  are  composed  of  cells. 
Animals  may  be  divided  into  those  consisting  of  a  single  cell 
(Protozoa),  and  those  made  up  of  a  multitude  of  cells  (Metazoa) ; 
but  in  every  case  the  animal  begins  as  a  single  cell  or  ovum 
from  which  all  the  other  cells,  however  different  finally  from 
one  another  either  in  form  or  function,  are  derived  by  processes 
of  growth  and  division ;  and,  as  will  be  seen  later,  the  whole 
organism  is  at  one  period  made  up  of  cells  practically  alike  in 
structure  and  behavior.  The  history  of  each  individual  animal 
or  plant  is  the  resultant  of  the  conjoint  histories  of  each  of  its 
cells,  as  that  of  a  nation  is,  when  complete,  the  story  of  the 
total  outcome  of  the  lives  of  the  individuals  composing  it. 

It  becomes,  therefore,  highly  important  that  a  clear  notion 
of  the  characters  of  the  cell  be  obtained  at  the  outset;  and 
this  chapter  will  be  devoted  to  presenting  a  general  account  of 
the  cell. 

The  cell,  whether  animal  or  vegetable,  in  its  most  complete 
form  consists  of  a  mass  of  viscid,  semifluid,  transparent  sub- 
stance (protoplasm),  a  cell  wall,  and  a  more  or  less  circular  body 
(nucleus)  situated  generally  centrally  within ;  in  which,  again, 
is  found  a  similar  structure  (nucleolus). 

This  description  applies  to  both  the  vegetable  and  the  ani- 
mal cell ;  but  the  student  will  find  that  the  greater  proportion 
of  animal  cells  have  no  cell  wall,  and  that  very  few  vegetable 
cells  are  without  it.  But  there  is  this  great  difference  between 
the  animal  and  vegetable  cell :  the  former  never  has  a  cellulose 
wall,  while  the  latter  rarely  lacks  such  a  covering.  In  every 
case  the  cell  wall,  whether  in  animal  or  vegetable  cells,  is  of 
greater  consistence  than  the  rest  of  the  cell.  This  is  especially 
true  of  the  vegetable  cell. 

It  is  doubtful  whether  there  are  any  cells  without  a  nucleus, 
while  not  a  few,  especially  when  young  and  most  active,  pos- 
sess several.  The  circular  form  may  be  regarded  as  the  typical 
form  of  both  cells  and  nuclei,  and  their  infinite  variety  in  size 
and  form  may  be  considered  as  in  great  part  the  result  of  the 
action  of  mechanical  forces,  such  as  mutual  pressure ;  this  is, 
of  course,  more  es^jecially  true  of  shape.  Reduced  to  its  great- 
est simplicity,  then,  the  cell  may  be  simply  a  mass  of  protoplasm 
with  a  nucleus. 


•  The  illustrations  of  the  sections  following  will  enable  the  student  to  form  a 
generalized  mental  picture  of  the  cell  in  all  its  parts. 


Q  ANIMAL  PHYSIOLOGY. 

It  seems  probable  that  the  numerous  researches  of  recent 
years  and  others  now  in  progress  will  open  up  a  new  world  of 
cell  biology  which  will  greatly  advance  our  knowledge,  espe- 
cially in  the  direction  of  increased  depth  and  accuracy. 

Though  many  points  are  still  in  dispute,  it  may  be  safely 
said  that  the  nucleus  plays,  in  most  cells,  a  role  of  the  highest 
importance ;  in  fact,  it  seems  as  though  we  might  regard  the 
nucleus  as  the  directive  brain,  so  to  speak,  of  the  individual 
cell.  It  frequently  happens  that  the  behavior  of  the  body  of 
the  cell  is  foreshadowed  by  that  of  the  nucleus.    Thus  fre- 


Fig.  1. — Nuclear  division.  A-H,  karyokinesis  of  a  tissue-cell.  A,  nuclear  reticulum  in  its  or- 
dinary state.  B,  preparing  for  division  ;  the  contour  is  less  defined,  and  the  fibers  thicker 
and  less  intricate.  C,  wreath-stage;  the  chromatin  is  arranged  in  a  complicated  looping 
round  the  equator  of  the  achromatin  spindle.  D,  monaster-stage  ;  the  chromatin  now 
appears  as  centripetal  equatorial  V's,  each  of  which  should  be  represented  as  double. 

E,  a  migration  of  the  half  of  each  chromatin  loop  towards  opposite  poles  of  the  spindle. 

F,  diaster-stage  ;  the  chromatin  forms  a  star,  round  each  pole  of  a  spindle,  each  aster  be- 
ing connected  by  strands  of  achromatin.  G,  daughter-wreath  stage  ;  the  newly  formed 
nuclei  are  passing  through  their  retrogressive  development,  which  is  completed  in  the 
resting  stage,  H.  d-f,  kar3'okinesis  of  an  egg-cell,  showing  the  smaller  amount  of  chro- 
matin than  in  the  tissue-cell.  The  stages  d,  e,  /,  correspond  to  D,  E,  F,  respectively.  The 
polar  star  at  the  end  of  the  spindle  is  composed  of  protoplasm-granules  of  the  cell  itself, 
and  must  not  be  mistaken  for  the  diaster  (F).  The  coarse  lines  represent  the  chromatin, 
the  fine  Unes  the  achromatin,  and  the  dotted  lines  cell-granules.  (Chiefly  modifled  from 
Flemming.)  X-Z,  direct  nuclear  division  in  the  cells  of  the  embryonic  integument  of  the 
Eui'opean  scorpion.    After  Blochmann  {Haddon). 


quently,  if  not  always,  division  of  the  body  of  the  nucleus  pre- 
cedes that  of  the  cell  itself,  and  is  of  a  most  complicated  char- 
acter (karyokinesis  or  mitosis).  The  cell  wall  is  of  subordinate 
importance  in  the  processes  of  life,  though  of  great  value  as  a 
mechanical  support  to  the  protoplasm  of  the  cell  and  the  aggre- 


THE  CELL.  7 

gations  of  cells  known  as  tissues.  The  greater  part  of  a  tree 
may  be  said  to  be  made  up  of  the  thickened  walls  of  the  cells, 
and  these  are  destitute  of  true  vitality,  unless  of  the  lowest 
order ;  while  the  really  active,  growing  part  of  an  old  and  large 
tree  constitutes  but  a  small  and  limited  zone,  as  may  be  learned 
from  the  plates  of  a  work  on  modern  botany  representing  sec- 
tions of  the  wood. 

Animals,  too,  have  their  rigid  parts,  in  the  adult  state  espe- 
cially, resulting  from  the  thickening  of  a  part  or  the  whole  of 
the  cell  by  a  deposition  usually  of  salts  of  lime,  as  in  the  case  of 
the  bones  of  animals.  But  in  some  cases,  as  in  cartilage,  the 
cell  wall  or  capsule  undergoes  thickening  and  consolidation, 
and  several  may  fuse  together,  constituting  a  matrix,  which  is 
also  made  up  in  part,  possibly,  of  a  secretion  from  the  cell  pro- 
toplasm. In  the  outer  parts  of  the  body  of  animals  we  have  a 
great  abundance  of  examples  of  thickening  and  hardening  of 
cells.  Very  well  known  instances  are  the  indurated  patches  of 
skin  {epithelium)  on  the  palms  of  the  hands  and  elsewhere. 

It  will  be  scarcely  necessary  to  remark  that  in  cells  thus 
altered  the  mechanical  has  largely  taken  the  place  of  the  vital 
in  function.  This  at  once  harmonizes  with  and  explains  what 
is  a  matter  of  common  observation,  that  old  men  are  less  active 
— have  less  of  life  within  them,  in  a  word,  than  the  young. 
Chemically,  the  cellulose  wall  of  plant-cells  consists  of  carbon, 
hydrogen,  and  oxygen,  in  the  same  relative  proportion  as  exists 
in  starch,  though  its  properties  are  very  different  from  those  of 
that  substance. 

Turning  to  cell  contents,  we  find  them  everywhere  made  up 
of  a  clear,  viscid  substance,  containing  almost  always  granules 
of  varying  but  very  minute  size,  and  differing  in  consistence, 
not  only  in  different  groups  of  cells,  but  often  in  the  same  cell, 
so  that  we  can  distinguish  an  outer  portion  {ectoplasm)  and  an 
inner  more  fluid  and  more  granular  region  {endoplasm). 

The  nucleus  is  a  body  with  very  clearly  defined  outline  (in 
some  cases  limited  by  a  membrane),  through  which  an  irregu- 
lar network  of  fibers  extends  that  stains  more  deeply  than  any 
other  part  of  the  whole  cell. 

Owing  to  the  fact  that  it  is  so  readily  changed  by  the  action 
of  reagents,  it  is  impossible  to  ascertain  the  exact  chemical  com- 
position of  living  protoplasm ;  in  consequence,  wo  can  only 
infer  its  chemical  structure,  etc.,  from  the  examination  of  the 
dead  substance. 

In  general,  it  may  be  said  that  protoplasm  belongs  to  the 


3  ANIMAL  PHYSIOLOGY. 

class  of  bodies  known  as  proteids— that  is,  it  consists  chemically 
of  carbon,  hydrogen,  a  little  sulphur,  oxygen,  and  nitrogen,  ar- 
ranged into  a  very  complex  and  unstable  molecule.  This  very 
instability  seems  to  explain  at  once  its  adaptability  for  the 
manifestation  of  its  nature  as  living  matter,  and  at  the  same 
time  the  readiness  with  which  it  is  modified  by  many  circum- 
stances ,  so  that  it  is  possible  to  understand  that  life  demands 
an  incessant  adaptation  of  internal  to  external  conditions. 

It  seems  highly  probable  that  protoplasm  is  not  a  single  pro- 
teid  substance,  but  a  mixture  of  such  ;  or  let  us  rather  say,  fur- 
nishes these  when  chemically  examined  and  therefore  dead. 

Very  frequently,  indeed  generally,  protoplasm  contains  other 
substances,  as  salts,  fat,  starch,  chlorophyl,  etc. 

From  the  fact  that  the  nucleus  stains  differently  from  the 
cell  contents,  we  may  infer  a  difference  between  them,  physical 
and  especially  chemical.  It  (nucleus)  furnishes  on  analysis  nu- 
clein,  which  contains  the  same  elements  as  protoplasm  (with  the 
exception  of  sulphur)  together  with  phosphorus.  Nuclei  have 
great  resisting  power  to  ordinary  solvents  and  even  the  digest- 
ive juices. 

Inasmuch  as  all  vital  phenomena  are  associated  with  proto- 
plasm, it  has  been  termed  the  "physical  basis  of  life^^  (Hux- 

ley). 

Tissues. — A  collection  of  cells  performing  a  similar  physio- 
logical action  constitutes  a  tissue. 

Generally  the  cells  are  held  together  either  by  others  with 
that  sole  function,  or  by  cement  material  secreted  by  them- 
selves. An  organ  may  consist  of  one  or  several  tissues.  Thus 
the  stomach  consists  of  muscular,  serous,  connective,  and  gland- 
ular tissues  besides  those  constituting  its  blood-vessels,  lym- 
phatics, and  nerves.  But  all  of  the  cells  of  each  tissue  have, 
speaking  generally,  the  same  function.  The  student  is  referred 
to  works  on  general  anatomy  and  histology  for  classifications 
and  descriptions  of  the  tissues. 

The  statements  of  this  chapter  will  find  illustration  in  the 
pages  immediately  following,  after  which  we  shall  return  to 
the  subject  of  the  cell  afresh. 

Summary. — The  typical  cell  consists  of  a  wall,  protoplasmic 
contents,  and  a  nucleus.  The  vegetable  cell  has  a  limiting 
membrane  of  cellulose.  Cells  undergo  differentiation  and  may 
be  united  into  groups  forming  tissues  which  serve  one  or  more 
definite  purposes. 

The  chemical  constitution  of  protoplasm  is  highly  complex 


UNICELLULAR  PLANTS.  9 

and  unstable.  The  nucleus  plays  a  prominent  part  in  the  life- 
history  of  the  cell,  and  seems  to  be  essential  to  its  perfect  devel- 
opment and  greatest  physiological  efficiency. 


UNICELLULAR  PLANTS. 
Yeast  (Torula,  Saccharomyces  CerevisicB). 

The  essential  part  of  the  common  substance,  yeast,  may  be 
studied  to  advantage,  as  it  affords  a  simple  type  of  a  vast  group 
of  organisms  of  profound 
interest  to  the  student  of 
physiology  and  medicine. 
To  state,  first,  the  main 
facts  as  ascertained  by 
observation  and  experi- 
ment : 

Morphological.  —  The 
particles  of  which  yeast 
is  composed  are  cells  of  a 
circular  or  oval  form,  of 
an  average  diameter  of 
about  yoVo  of  ^^  inch. 

Each  individual  torula 
cell  consists  of  a  trans- 
parent homogeneous  cov- 
ering (cellulose)  and  gran- 
ular semifluid  contents 
(protoplasm).  Within  the 
latter  there  may  be  a 
space  (vacuole)  filled  with 
more  fluid  contents. 

The  various  cells  pro- 
duced by  budding  may 
remain  united  like  strings 
of  beads.  Collections  of 
masses  composed  of  four 
or  more  subdivisions  (as- 
cospores),  which  finally 
separate  by  rupture  of 
the  original  cell  wall,  having  thus  become  themselves  inde 
XJendent  cells,  may  be  seen  more  rarely  (endogenous  division). 


Fig.  2. — Various  stages  in  the  development  of  brewer's 
yeast,  seen,  with  the  exception  of  the  first  in  the 
series,  with  an  ordinary  high  power  (Zeiss,  D.  4)  of 
the  microscope.  The  first  is  greatly  magnified 
(Gundlach's  t'j  immersion  lens).  The  second  series 
of  four  represents  stages  in  the  division  of  a  single 
cell ;  and  the  third  series  a  branching  colony. 
Everywhere  the  light  areas  indicate  vacuoles. 


Fio.  3.— The  endogonidia  (ascospore)  phase  of  repro- 
duction— i.  e.,  endogenous  division. 


Fio.  4.— Further  development  of  the  forms  represented 
in  Fig.  3. 


IQ  ANIMAL   PHYSIOLOGY. 

The  yeast-cell  is  now  believed  to  possess  a  nucleus. 

Chemical. — When  yeast  is  burned  and  the  ashes  analyzed, 
they  are  found  to  consist  chiefly  of  salts  of  potassium,  calcium, 
and  magnesium. 

The  elements  of  which  yeast  is  composed  are  C,  H,  O,  N,  S, 
P,  K,  Mg,  and  Ca ;  but  chiefly  the  first  four. 

Physiological. — If  a  little  of  the  powder  obtained  by  drying 
yeast  at  a  temperature  below  blood-heat  be  added  to  a  solution 
of  sugar,  and  the  latter  be  kept  warm,  bubbles  of  carbon  di- 
oxide will  be  evolved,  causing  the  mixture  to  become  frothy ; 
and  the  fluid  will  acquire  an  alcoholic  character  {fermenta- 

ti07l). 

If  the  mixture  be  raised  to  the  boiling-point,  the  process  de- 
scribed at  once  ceases. 

It  may  be  further  noticed  that  in  the  fermenting  saccharine 
solution  there  is  a  gradual  increase  of  turbidity.  All  of  these 
changes  go  on  perfectly  well  in  the  total  absence  of  sunlight. 

Yeast-cells  are  found  to  grow  and  reproduce  abundantly  in 
an  artificial  food  solution  consisting  of  a  dilute  solution  of  cer- 
tain salts,  together  with  sugar. 

Conclusions. — What  are  the  conclusions  which  may  be  legiti- 
mately drawn  from  the  above  facts  ? 

That  the  essential  part  of  yeast  consists  of  cells  of  about  the 
size  of  mammalian  blood-corpuscles,  but  with  a  limiting  wall 
of  a  substance  different  from  the  inclosed  contents,  which  latter 
is  composed  chiefly  of  that  substance  common  to  all  living 
things — protoplasm ;  that  like  other  cells  they  reproduce  their 
kind,  and  in  this  instance  by  two  methods :  gemmation  giving 
rise  to  the  bead-like  aggregations  alluded  to  above ;  and  in- 
ternal division  of  the  protoplasm  {endogenous  division). 

From  the  circumstances  under  which  growth  and  reproduc- 
tion take  place,  it  will  be  seen  that  the  original  protoplasm  of 
the  cells  may  increase  its  bulk  or  grow  when  supplied  with 
suitable  food,  which  is  not,  as  will  be  learned  later,  the  same  in 
all  respects  as  that  on  which  green  plants  thrive ;  and  that  this 
may  occur  in  darkness.  But  it  is  to  be  especially  noted  that  the 
protoplasm  resulting  from  the  action  of  the  living  cells  is 
wholly  different  from  any  of  the  substances  used  as  food.  This 
power  to  construct  protoplasm  from  inanimate  and  unorgan- 
ized materials,  reproduction,  and  fermentation  are  all  proper- 
ties characteristic  of  living  organisms  alone. 

It  will  be  further  observed  that  these  changes  all  take  place 
within  narrow  limits  of  temperature;  or,  to  put  the  matter 


UNICELLULAR  PLANTS. 


11 


more  generally,  that  the  life-history  of  this  humble  organism 
can  only  be  unfolded  under  certain  well-defined  conditions. 

Protococcus  {Protococcus  pluvialis). 

The  study  of  this  one-celled  plant  will  afford  instructive 
comparison  between  the  ordinary  green  plant  and  the  colorless 
plants  or  fungi. 

Like  Torula  it  is  selected  because  of  its  simple  nature,  its 
abundance,  and  the  ease  with  which  it  may  be  obtained,  for  it 
abounds  in  water-barrels,  standing  pools,  drinking-troughs,  etc. 

Morphological. — Protococcus  consists  of  a  structureless  wall 
and  viscid  granular  contents,  i.  e.,  of  cellulose  and  protoplasm. 

The  protoplasm  may  contain  starch  and  a  red  or  green  color- 
ing matter  {chloropliyl).  It  probably  contains  a  nucleus.  The 
cell  is  mostly  globular  in  form. 


Fig.  5. 


Fig.  G. 


7tC 


Fig. 


Figs.  5  to  7  represent  successive  stages  observed  in  the  life-history  of  Protococci  scraped  from 
the  bark  of  a  tree. 

Fig.  5.— a  group  in  the  dried  .state,  illustrating  method  of  division. 

Fig.  6. — One  of  the  above  after  two  days'  immersion  in  water. 

Fig.  7.— Various  phases  in  the  later  motile  stage  assumed  by  the  above  specimens.  The  nu- 
cleus is  denoted  by  nc ;  the  cell  wall  by  c.w  ;  and  the  coloring-matter  by  the  dark  spot. 
On  the  left  of  Fig.  7  an  individual  may  be  seen  that  is  devoid  of  a  cell  wall. 

Physiological — It  reproduces  by  division  of  the  original  cell 
(fission)  into  similar  individuals,  and  by  a  process  of  budding 
and  constriction  ((jemmation)  which  is  much  rarer.  Under  the 
influence  of  sunlight  it  decomposes  carbon  dioxide  (CO,),  fix- 
ing the  carbon  and  setting  the  oxygen  free.  It  can  flourish  per- 
fectly in  rain-vvator,  which  contains  only  carbon  dioxide,  salts 
of  ammonium,  and  minute  quantities  of  other  soluble  salts  that 
may  as  dust  have  been  blown  into  it. 

There  is  a  motile  form  of  this  unicellular  plant,  and  in  this 
stage  it  moves  through  tlio  fluid  in  which  it  lives  by  means  of 


12  ANIMAL  PHYSIOLOGY. 

extensions  of  its  protoplasm  {cilia)  through  the  cell  wall;  or 
the  cell  wall  may  disappear  entirely.  Finally,  the  motile  form, 
withdrawing  its  cilia  and  clothing  itself  with  a  cellulose  coat, 
becomes  globular  and  passes  into  a  quiescent  state  again. 
Much  of  this  part  of  its  history  is  common  to  lowly  animal 
forms. 

Conclusions. — It  will  be  seen  that  there  is  much  in  common 
in  the  life-history  of  Torula  and  Protococcus.  By  virtue  of  be- 
ing living  protoplasm  they  transform  unorganized  material  into 
their  own  substance ;  and  they  grow  and  reproduce  by  analo- 
gous methods. 

But  there  are  sharply  defined  differences.  For  the  green 
plant  sunlight  is  essential,  in  the  presence  of  which  its  chloro- 
phyl  prepares  the  atmosphere  for  animals  by  the  removal  of 
carbonic  anhydride  and  the  addition  of  oxygen,  while  for 
Torula  neither  this  gas  nor  sunlight  is  essential. 

Moreover,  the  fungus  {Torula)  demands  a  higher  kind  of 
food,  one  more  nearly  related  to  the  pabulum  of  animals ;  and 
is  absolutely  independent  of  sunlight,  if  not  actually  injured 
by  it ;  not  to  mention  the  remarkable  process  of  fermentation. 


UNICELLAR  ANIMALS. 
The  Proteus  Animalcule  {Amoeba). 

In  order  to  illustrate  animal  life  in  its  simpler  form  we 
choose  the  above-named  creature,  which  is  nearly  as  readily 
obtainable  as  Protococcus  and  often  under  the  same  circum- 
stances. 

Morphological. — Amoeha  is  a  microscopic  mass  of  transparent 
protoplasm,  about  the  size  of  the  largest  of  the  colorless  blood- 
corpuscles  of  cold-blooded  animals,  with  a  clearer,  more  con- 
sistent outer  zone  {ectosarc),  (although  without  any  proper  cell 
wall),  and  a  more  fluid,  granular  inner  part.  A  clear  space 
{contractile  vesicle,  vacuole)  makes  its  appearance  at  intervals  in 
the  ectosarc,  which  may  disappear  somewhat  suddenly.  This 
appearance  and  vanishing  have  suggested  the  term  pulsating 
or  contracting  vesicle.  Both  a  nucleus  and  nucleolus  may  be 
seen  in  Amoeba.  At  varying  short  periods  certain  parts  of  its 
body  { pseudopodia)  are  thrust  out  and  others  withdrawn. 

Physiological. — Amoeba  can  not  live  on  such  food  as  proves 
adequate  for  either  Protococcus  or  Torula,  but  requires,  besides 


UNICELLAR  ANIMALS. 


13 


inorganic  and  unorganized  food,  also  organized  matter  in  the 
form  of  a  complex  organic  compound  known  as  protein,  which 


Fig.  9. 


Fig.  10. 


Fig.  11. 


Fig.  12. 


Fig.  13. 


Fig.  14. 


Fig.  15. 


Fig.  16. 


Figs.  8  to  15,  represent  successive  phases  in  the  life-history  of  an  Amoeboid  organism,  kept 
under  constant  observation  for  three  days  ;  Fig.  16  a  similar  organism  encysted,  which 
was  a  few  hours  later  set  free  by  the  disintegration  of  the  cyst.  (All  the  figures  are 
drawn  under  Zeiss,  D.  3.) 

Fig.  8.— The  locomotor  phase  ;  the  ectoplasm  is  seen  protruding  to  form  a  pseudopodium,  into 
which  the  endopla,sm  pa.sses. 

Fig.  9.— a  stage  in  the  ingestive  phase.  A  vegetable  organism,  fp,  is  undergoing  intussus- 
ception. 

Fig.  10.— a  portion  of  the  creature  represented  in  Fig.  9  after  complete  ingestion  of  the  food- 
particle. 

Figs.  H,  12.— Successive  stages  in  the  a.ssimilative  and  excretory  processes.  Fig.  12  repre- 
sents the  organism  some  twenty  hours  later  than  as  seen  in  Fig.  11.  The  undigested  rem- 
nant* of  the  ingested  organism  are  represented  undergoing  ejection  (excretion)  at  fp,  in 
Fig.  12. 

Figs.  1.3,  \4.  15.  represent  successive  stages  in  the  reproductive  process  of  the  same  individ- 
ual, observed  two  days  later.    It  will  be  noticed  (Fig.  13)  that  the  nucleus  divides  first. 

In  the  above  figures,  vc,  denotes  the  contracting  vacuole  ;  nc,  the  nucleus  ;  ps,  pseudopo- 
dium ;  dt,  diatom  ;  fp,  food-particle. 

contains  nitrogen  in  addition  to  carbon,  hydrogen,  and  oxygen. 
In  fact,  Amrjiba  can  prey  upon  both  plants  and  animals,  and 
thus  use  up  as  food  protoj^lasm  itself.     The  pseudopodia  serve 
the  double  purpose  of  organs  of  locomotion  and  prehension. 
This  creature  absorbs  oxygen  and  evolves  carbon  dioxide. 


14  ANIMAL  PHYSIOLOGY. 

Inasmuch  as  any  part  of  the  body  may  serve  for  the  admission, 
and  possibly  the  digestion,  of  food  and  the  ejection  of  the  use- 
less remains,  we  are  not  able  to  define  the  functions  of  special 
parts.  Amoeba  exercises,  however,  some  degree  of  choice  as  to 
what  it  accepts  or  rejects. 

The  movements  of  the  pseudopodia  cease  when  the  tempera- 
ture of  the  surrounding  medium  is  raised  or  lowered  beyond  a 
certain  point.  It  can,  however,  survive  in  a  quiescent  form 
greater  depression  than  elevation  of  the  temperature.  Thus,  iat 
35°  C,  heat-rigor  is  induced ;  at  40°  to  45°  C,  death  results ;  but 
though  all  movement  is  arrested  at  the  freezing-point  of  water, 
recovery  ensues  if  the  temperature  be  gradually  raised.  Its 
form  is  modified  by  electric  shocks  and  chemical  agents,  as  well 
as  by  variations  in  the  temperature.  At  the  present  time  it  is 
not  possible  to  define  accurately  the  functions  of  the  vacuoles 
found  in  any  of  the  organisms  thus  far  considered.  It  is 
worthy  of  note  that  Amoeba  may  spontaneously  assume  a 
spherical  form,  secrete  a  structureless  covering,  and  remain  in 
this  condition  for  a  variable  period,  reminding  us  of  the  similar 
behavior  of  Torula. 

Amoeba  reproduces  by  fission,  in  which  the  nucleus  takes  a 
prominent  if  not  a  directive  part,  as  seems  likely  it  does  in  re- 
gard to  all  the  functions  of  unicellular  organisms. 

Conclusions. — It  is  evident  that  Amoeba  is,  in  much  of  its  be- 
havior, closely  related  to  both  colored  and  colorless  one-celled 
plants.  All  of  the  three  classes  of  organisms  are  composed  of 
protoplasm  ;  each  can  construct  protoplasm  out  of  that  which  is 
very  different  from  it ;  each  builds  up  the  inanimate  inorganic 
world  into  itself  by  virtue  of  that  force  which  we  call  vital,  but 
which  in  its  essence  we  do  not  understand ;  each  multiplies  by 
division  of  itself,  and  all  can  only  live,  move,  and  have  their 
being  under  certain  definite  limitations.  But  even  among 
forms  of  life  so  lowly  as  those  we  have  been  considering,  the 
differences  between  the  animal  and  vegetable  worlds  appear. 
Thus,  Amoeba  never  has  a  cellulose  wall,  and  can  not  subsist 
on  inorganic  food  alone.  The  cellulose  wall  is  not,  however, 
invariably  present  in  plants,  though  this  is  generally  the  case ; 
and  there  are  animals  (Ascidians)  with  a  cellulose  investment. 
Such  are  very  exceptional  cases.  But  the  law  that  animals 
must  have  organized  material  {protein)  as  food  is  without  ex- 
ception, and  forms  a  broad  line  of  distinction  between  the  ani- 
mal and  vegetable  kingdoms. 

Amoeba   will  receive    further   consideration  later;    in  the 


PARASITIC   ORGANISMS.  15 

mean  time,  we  turn  to  tlie  study  of  forms  of  life  in  many  respects 
intermediate  between  plants  and  animals,  and  full  of  practical 
interest  for  mankind,  on  account  of  their  relations  to  disease, 
as  revealed  by  recent  investigations. 


PARASITIC  ORGANISMS. 

The  Fungi. 
Molds  {Penicillium  Olaucum  and  Mucor  Mucedo). 

Closely  related  to  Torida  physiologically,  but  of  more  com- 
plex structure,  are  the  molds,  of  which  we  select  for  convenient 
study  the  common  green  mold  {Penicillium),  found  growing  in 
dark  and  moist  places  on  bread  and  similar  substances,  and  the 
white  mold  {Mucor),  which  grows  readily  on  manure. 

The  fungi  originate  in  spores,  which  are  essentially  like 
Torula  in  structure,  by  a  process  of  budding  and  longitudinal 
extension,  resulting  in  the  formation  of  transparent  branches 
or  tubules,  filled  with  protoplasm  and  invested  by  cellulose 
walls,  across  which  transverse  partitions  are  found  at  regular 
intervals,  and  in  which  vacuoles  are  also  visible. 

The  spores,  when  growing  thus  in  a  liquid,  give  rise  to  up- 
ward branches  {aerial  hypha),  and  downward  branches  or  root- 
lets {submerged  hyplioe).  These  multitudinous  branches  inter- 
lace in  every  direction,  forming  an  intricate  felt-work,  which 
supports  the  green  powder  (spores)  which  may  be  so  easily 
shaken  off  from  a  growing  mold.  In  certain  cases  the  aerial 
hyphse  terminate  in  tufts  of  branches,  which,  by  transverse 
division,  become  split  up  into  spores  {Conidia),  each  of  which 
is  similar  in  structure  to  a  yeast-cell. 

The  green  coloring  matter  of  the  fungi  is  not  chlorophyl. 
The  Conidia  germinate  under  the  same  conditions  as  Torula. 

Mucor  Mucedo. — The  growth  and  development  of  this  mold 
may  be  studied  by  simply  inverting  a  glass  tumbler  over  some 
horse-dung  on  a  saucer,  into  which  a  very  little  water  has 
been  poured,  and  keeping  the  preparation  in  a  warm  place. 

Very  soon  whitish  filaments,  gradually  getting  stronger,  ap- 
pear, and  are  finally  topped  by  rounded  heads  or  spore-cases 
{Sporangia).  These  filaments  are  the  hypJue,  similar  in  struct- 
ure to  those  of  Penicillium.  The  spore-case  is  lil](;d  with  a 
multitude  of  oval  bodies  {spores),  resulting  from  the  subdivis- 
ion of  the  protof>lasm,  which  are  finally  released  by  the  spore- 


16 


ANIMAL  PHYSIOLOGY. 


Fig.  27, 


Fig.  2a 


PARASITIC  ORGANISMS.  j^ 

Figs.  17  to  38.— In  the  following  figures,  ha,  denotes  aerial  hyphae  ;  sp,  sporangium  :  zy,  zy- 
gospore :  ex.  exosporium  ;  my,  mycelium  ;  mc,  mucilage  ;  cl,  columella  ;  en,  endogonidia. 

Fig.  1~.— Spore-bearing  hyphae  of  Mucor.  growing  from  horse-dung. 

Fig.  18. — The  same,  teased  out  with  needles  (A,  4). 

Figs.  19,  20,  21.— Successive  stages  in  the  development  of  the  sporangium. 

P^G.  22. — Isolated  spores  of  Mucor. 

Fig.  23. — Grerminating  spores  of  the  same  mold. 

Fig.  24.— Successive  stages  in  the  germination  of  a  single  spore. 

Figs.  25,  26,  27.— Successive  phases  in  the  conjugative  process  of  Mucor. 

Fig.  28. — Successive  stages  observed  during  ten  hours  in  the  growth  of  a  conidiophore  of  Peni- 
cillium  in  an  object-glass  culture  (D,  4). 

case  becoming  thinned  to  the  point  of  rupture.  The  devel- 
opment of  these  spores  takes  place  in  substantially  the  same 
manner  as  those  of  Penicillium.  Sporangia  developing  spores 
in  this  fashion  by  division  of  the  protoplasm  are  termed  asci, 
and  the  spores  ascospores. 

So  long  as  nourishment  is  abundant  and  the  medium  of 
growth  fluid,  this  asexual  method  of  reproduction  is  the  only 
one ;  but,  under  other  circumstances,  a  mode  of  increase,  known 
as  conjugation,  arises.  Two  adjacent  hyphae  enlarge  at  the  ex- 
tremities into  somewhat  globular  heads,  bend  over  toward  each 
other,  and,  meeting,  their  opposed  faces  become  thinned,  and 
the  contents  intermingle.  The  result  of  this  union  (zygosjjore) 
undergoes  now  certain  further  changes,  the  cellulose  coat  being 
separated  into  two — an  outer,  darker  in  color  (exosporium),  and 
an  inner  colorless  one  (endosporium). 

Under  favoring  circumstances  these  coats  burst,  and  a 
branch  sprouts  forth  from  which  a  vertical  tube  arises  that 
terminates  in  a  sporangium,  in  which  spores  arise,  as  before  de- 
scribed. It  will  be  apparent  that  we  have  in  Mucor  the  exem- 
plification of  what  is  known  in  biology  as  "  alternation  of  gen- 
erations"— that  is,  there  is  an  intermediate  generation  be- 
tween the  original  form  and  that  in  which  the  original  is 
again  reached. 

Physiologically  the  molds  closely  resemble  yeast,  some  of 
them,  as  Mucor,  being  capable  of  exciting  a  fermentation. 

The  fungi  are  of  special  interest  to  the  medical  student,  be- 
cause many  forms  of  cutaneous  disease  are  directly  associated 
with  their  growth  in  the  epithelium  of  the  skin,  as,  for  exam- 
ple, common  ringworm  ;  and  their  great  vitality,  and  the  facil- 
ity with  which  their  spores  are  widely  dispersed,  explain  the 
highly  contagious  nature  of  such  diseases.  The  media  on  which 
they  flourish  (feed)  indicates  their  great  physiological  differ- 
ences in  this  particular  from  the  green  plants  proper.  They  are 
closely  related  in  not  a  f(!W  respects  to  an  important  class  of 
vegetable  organisms,  known  as  bacteria,  to  be  considered  forth- 
with, 

2 


18 


ANIMAL  PHYSIOLOGY. 


The  Bacteria. 

The  bacteria  include  numberless  varieties  of  organisms  of 
extreme  minuteness,  many  of  them  visible  only  by  the  help  of 
the  most  powerful  lenses.  Their  size  has  been  estimated  at 
from  30^00  to  To-ooT  <^f  ^'^  inch  in  diameter. 

They  grow  mostly  in  the  longitudinal  direction,  and  repro- 
duce by  transverse  division,  forming  spores  from  which  new 
generations  arise. 

Some  of  them  have  vibratile  cilia,  while  the  cause  of  the 
movements  of  others  is  quite  unknown. 

As  in  many  other  lowly  forms  of  life,  there  is  a  quiescent 
as  well  as  an  active  stage.     In  this  stage  {zooglcea  form)  they 


Fig.  33. 


Fig.  32. 


Fig.  29.— Micrococcus,  very  like  a  spore,  but  usually  much  smaller. 

Fig.  30.— Bacterium. 

Fig.  31.— Bacillus.    The  central  filament  presented  this  segmented  appearance  as  the  result  of 

I-     %W°%^^? .?/  transverse  division  occurring  during  ten  minutes'  observation. 

i  IG.  d^.— bpinllum  :  various  forms.    The  first  two  represent  vibrio,  which  is  possibly  only  a 

stage  of  spirillum.  f  j        j 

Fig.  33.— a  drop  of  the  surface  scum,  showing  a  spirillum  aggregate  in  the  resting  state. 

are  surrounded  by  a  gelatinous  matter,  probably  secreted  by 
themselves. 


PARASITIC  ORGANISMS.  19 

Bacteria  grow  and  reproduce  in  Pasteur's  solution,  render- 
ing it  opaque,  as  well  as  in  almost  all  fluids  that  abound  in 
proteid  matter.  That  such  fluids  readily  putrefy  is  owing  to 
the  presence  of  bacteria,  the  vital  action  of  which  suffices  to 
break  asunder  complex  chemical  compounds  and  produce  new 
ones.  Some  of  the  bacteria  require  oxygen,  as  Bacillus  an- 
fhracis,  while  others  do  not,  as  the  organism  of  putrefaction, 
Bacterium  terino. 

Bacteria  are  not  so  sensitive  to  slight  variations  in  tempera- 
ture as  most  other  organisms.  They  can,  many  of  them,  with- 
stand freezing  and  high  temperatures.  All  bacteria  and  all 
germs  of  bacteria  are  killed  by  boiling  water,  though  the  spores 
are  much  more  resistant  than  the  mature  organisms  themselves. 
Some  spores  can  resist  a  dry  heat  of  140°  C. 

The  spores,  like  Torula  and  Protococcus,  bear  drying,  with- 
out loss  of  vitality,  for  considerable  periods. 

That  different  groups  of  bacteria  have  a  somewhat  different 
life-history  is  evident  from  the  fact  that  the  presence  of  one 
checks  the  other  in  the  same  fluid,  and  that  successive  swarms 
of  different  kinds  may  flourish  where  others  have  ceased  to 
live. 

That  these  organisms  are  enemies  of  the  constituent  cells  of 
the  tissues  of  the  highest  mammals  has  now  been  abundantly 
demonstrated.  That  they  interfere  with  the  normal  working 
of  the  organism  in  a  great  variety  of  ways  is  also  clear ;  and 
certain  it  is  that  the  harm  they  do  leads  to  aberration  in  cell- 
life,  however  that  may  be  manifested.  They  rob  the  tissues  of 
their  nutriment  and  oxygen,  and  poison  them  by  the  products 
of  the  decompositions  they  produce.  But  apart  from  this,  their 
very  presence  as  foreign  agents  must  hamper  and  derange  the 
delicate  mechanism  of  cell-life. 

These  organisms  seem  to  people  the  air,  land,  and  waters 
with  invisible  hosts  far  more  numerous  than  the  forms  of  life 
we  behold.  Fortunately,  they  are  not  all  dangerous  to  the 
higher  forms  of  mammalian  life ;  but  that  a  large  proportion 
of  the  diseases  which  afflict  both  man  and  the  domestic  animals 
are  directly  caused,  in  the  sense  of  being  invariably  associated 
with,  the  presence  of  such  forms  of  life,  is  now  beyond  doubt. 

The  facts  stated  above  explain  why  that  should  be  so ;  why 
certain  maladies  should  be  infectious;  how  the  germs  of  dis- 
ease may  bo  transported  to  a  friend  wrapped  up  in  tin;  fohls  of 
a  letter. 

Disease  thus  caused,  it  must  not  be  forgotten,  is  an  illustra- 


20  ANIMAL  PHYSIOLOGY. 

tion  of  the  struggle  for  existence  and  tlie  survival  of  the  fittest. 
If  the  cells  of  an  organism  are  mightier  than  the  bacteria^  the 
latter  are  overwhelmed ;  but  if  the  bacteria  are  too  great  in 
numbers  or  more  vigorous,  the  cells  must  yield ;  the  battle  may 
waver — now  dangerous  disease,  now  improvement — but  in  the 
end  the  strongest  in  this,  as  in  other  instances,  prevail. 


UNICELLULAR   ANIMALS  WITH    DIFFERENTIATION    OF 
STRUCTURE. 

The  Bell-Animalcule  (Voriicella). 

Amoeba  is  an  example  of  a  one-celled  animal  with  little  per- 
ceptible differentiation  of  structure  or  corresponding  division 
of  physiological  labor.  This  is  not,  however,  the  case  with  all 
unicellular  animals,  and  we  proceed  to  study  one  of  these  with 
considerable  development  of  both.  The  Bell  -  animalcule  is 
found  in  both  fresh  and  salt  water,  either  single  or  in  groups. 
It  is  anchored  to  some  object  by  a  rope-like  stalk  of  clear  pro- 
toplasm, that  has  a  spiral  appearance  when  contracted;  and 
which,  with  a  certain  degree  of  regularity,  shortens  and  length- 
ens alternately,  suggesting  that  more  definite  movement  (con- 
traction) of  the  form  of  protoplasm  known  as  inuscle,  to  be 
studied  later. 

The  body  of  the  creature  is  bell-shaped,  hence  its  name ;  the 
bell  being  provided  with  a  thick  everted  lip  (peristome),  covered 
with  bristle-like  extensions  of  the  protoplasm  (cilia),  which  are 
in  almost  constant  rhythmical  motion.  Covering  the  mouth  of 
the  bell  is  a  lid,  attached  by  a  hinge  of  protoplasm  to  the  body, 
which  may  be  raised  or  lowered.  A  wide,  funnel -like  depres- 
sion ((Esophagus)  leads  into  the  softer  substance  within  which 
it  ends  blindly.  The  outer  part  of  the  animal  (cuticula)  is 
denser  and  more  transparent  than  any  other  part  of  the  whole 
creature ;  next  to  this  is  a  portion  more  granular  and  of  inter- 
mediate transparency  between  the  external  and  innermost 
portions  (cortical  layer).  Below  the  disk  is  a  space  (contractile 
vesicle)  filled  with  a  thin,  clear  fluid,  which  may  be  seen  to 
enlarge  slowly  and  then  to  collapse  suddenly.  When  the  Yorti- 
cella  is  feeding,  these  vesicles  may  contain  food-particles,  and 
in  the  former,  apparently,  digestion  goes  on.  Such  food  vacu- 
oles (vesicles)  may  circulate  up  one  side  of  the  body  of  the  ani- 
mal and  down  the  other.  Their  exact  significance  is  not  known, 
but  it  would  appear  as  if  digestion  went  on  within  them ;  and 


UNICELLULAR  ANIMALS. 


21 


possibly  th-e  clear  fluid  with  which  they  are  filled  may  be  a  spe- 
cial secretion  with  solvent  action  on  food. 


Fig.  37. 


Fig.  38. 


Fig.  39. 


Figs.  34  to  40.— In  the  following  figures  d.  denotes  disc  ; 
p,  peristome  ;  vc,  contractile  vacuole ;  vf,  food- 
vacuole  ;  rs,  vestibule  :  cf,  contractile  fiber  ;  c, 
cyst  ;  nc,  nucleus  ;  cl,  cilium. 

Fig.  34.— a  group  of  vorticellse  showing  the  creature  in 
various  positions  (A,  3). 

Fig.  35.— The  sane,  in  the  extended  and  in  the  retracted 
state.     (Surface  views.) 

Fig.  36.— Shows  food-vacuoles  ;  one  in  the  act  of  inges- 
tion. 

Fig.  37.— a  vorticella,  in  which  the  process  of  multiplica- 
tion by  fission  is  begun. 

Fig.  38.  — the  results  of  fission  ;  the  production  of  two  in- 
dividuals of  unequal  size. 

Fig.  39.— Illustration  of  reproduction  by  conjugation. 

Fig.  40.— An  encysted  vorticella. 


Fig.  35 


Situated  somewhat  centrally  is  a  horseshoe-shaped  body, 
with  well-defined  edges,  which  stains  more  readily  than  the  rest 
of  the  cell,  indicating  a  different  chemical  composition ;  and, 
from  the  prominent  part  it  takes  in  the  reproductive  and  other 
functions  of  the  creature,  it  may  be  considered  the  nucleus 
{endoplasf). 

Multiplication  of  the  species  is  either  by  gemmation  or  by 
fission.  In  the  first  case  the  nucleus  divides  and  the  fragments 
are  transformed  into  locomotive  germs;  in  the  latter  the  entire 
animal,  including  the  nucleus,  divides  longitudinally, each  half 
becoming  a  similar  complete,  independent  organism.     Still  an- 


22  ANIMAL  PHYSIOLOGY. 

other  metliod  of  reproduction  is  known.  A  more  or  less  globu- 
lar body  encircled  with  a  ring  of  cilia  and  of  relatively  small 
size  may  sometimes  be  seen  attached  to  the  usual  form  of  Vorti- 
cella,  with  which  it  finally  becomes  blended  into  one  mass.  This 
seems  to  foreshadow  the  "'  sexual  conjugation  "  of  higher  forms, 
and  is  of  great  biological  significance. 

Vorticella  may  pass  into  an  encysted  and  quiescent  stage  for 
an  indefinite  period  and  again  become  active.  The  history  of 
the  Bell-animalcule  is  substantially  that  of  a  vast  variety  of 
one-celled  organisms  known  as  Infusoria,  to  which  Amoeba 
itself  belongs.  It  will  be  observed  that  the  resemblance  of  this 
organism  to  Amoeba  is  very  great ;  it  is,  however,  introduced 
here  to  illustrate  an  advance  in  differentiation  of  structure ;  and 
to  show  how,  with  the  latter,  there  is  usually  a  physiological 
advance  also,  since  there  is  additional  functional  progress  or 
division  of  labor;  but  still  the  whole  of  the  work  is  done  with- 
in one  cell.  Amoeba  and  Vorticella  are  both  factories  in  which 
all  of  the  work  is  done  in  one  room,  but  in  the  latter  case  the 
machinery  is  more  complex  than  in  the  former  ;  there  are  cor- 
respondingly more  processes,  and  each  is  performed  with  greater 
perfection.  Thus,  food  in  the  case  of  the  Bell-animalcule  is 
swept  into  the  gullet  by  the  currents  set  up  by  the  multitudes 
of  vibrating  arms  around  this  opening  and  its  immediate  neigh- 
borhood ;  the  contractile  vesicles  play  a  more  prominent  part ; 
and  the  waste  of  undigested  food  is  ejected  at  a  more  definite 
portion  of  the  body,  the  floor  of  the  oesophagus ;  while  all  the 
movements  of  the  animal  are  rhythmical  to  a  degree  not  exem- 
plified in  such  simple  forms  as  Amoeba;  not  to  mention  its 
various  resources  for  multiplication  and,  therefore,  for  its 
perpetuation  and  permanence  as  a  species.  It,  too,  like  all  the 
unicellular  organisms  we  have  been  considering,  is  susceptible 
of  very  wide  distribution,  being  capable  of  retaining  vitality  in 
the  dried  state,  so  that  these  infusoria  may  be  carried  in  vari- 
ous directions  by  winds  in  the  form  of  microscopic  dust. 


MULTICELLULAR  ORGANISMS. 

The  Fresh-Water  Polyps  {Hydra  viridis  j  Hydra  fusca). 

The  comparison  of  an  animal  so  simple  in  structure,  though 
made  up  of  many  cells,  as  the  Polyp,  with  the  more  complex 
organizations  with  which  we  shall  have  especially  to  deal,  may 


MULTICELLULAR  ORGANISMS.  23 

be  fitly  undertaken  at  this  stage.  The  Polyps  are  easily  obtain- 
able from  ponds  in  which  they  are  found  attached  to  various 
kinds  of  weeds.  To  the  naked  eye,  they  resemble  translucent 
masses  of  jelly  with  a  greenish  or  reddish  tinge.  They  range 
in  size  from  one  quarter  to  one  half  an  inch ;  are  of  an  elongated 
cylindrical  form  ;  provided  at  the  oral  extremity  with  thread- 
like tentacles  of  considerable  length,  which  are  slowly  moved 
about  in  all  directions ;  but  they  and  the  entire  body  may  short- 
en rapidly  into  a  globular  mass.  They  are  usually  attached  at 
the  opposite  (aboral)  pole  to  some  object,  but  may  float  free,  or 
slowly  crawl  from  place  to  place.  It  may  be  observed,  under 
the  microscope,  that  the  tentacles  now  and  then  embrace  some 
living  object,  convey  it  toward  an  opening  (mouth)  near  their 
base,  from  which,  from  time  to  time,  refuse  material  is  cast  out. 
It  may  be  noticed,  too,  that  a  living  object  within  the  touch  of 
these  tentacles  soon  loses  the  power  to  struggle,  which  is  owing 
to  the  peculiar  cells  (netUe -cells,  urticating  capsules,  nemato- 
cysts)  with  which  they  are  abundantly  provided,  and  which  se- 
crete a  poisonous  fluid  that  paralyzes  prey. 

The  mouth  leads  into  a  simple  cavity  {coelom)  in  which 
digestion  proceeds.  The  green  color  in  Hydra  viridis,  and  the 
red  color  of  Hydra  fusca,  is  owing  to  the  presence  of  clilorophyl, 
the  function  of  which  is  not  known.  Hydra  is  structurally  a 
sac,  made  up  of  two  layers  of  cells,  an  outer  {ectoderm)  and 
an  inner  (endoderm)  ;  the  tentacles  being  repetitions  of  the 
structure  of  the  main  body  of  the  animal,  and  so  hollow  and 
composed  of  two  cell  layers.  Speaking  generally,  the  outer 
layer  is  devoted  to  obtaining  information  of  the  surroundings; 
the  inner  to  the  work  of  preparing  nutriment,  and  probably, 
also,  discharging  waste  matters,  in  which  latter  assistance  is 
also  received  from  the  outer  layer.  As  digestion  takes  place 
largely  within  the  cells  themselves,  or  is  intracellular,  we  are 
reminded  of  Varticella  and  still  more  of  Amoeba.  There  is  in 
Hydra  a  general  advance  in  development,  but  not  very  much  in- 
dividual cell  sx>ecialization.  That  of  the  urticating  capsules  is 
one  of  the  best  examples  of  such  sj^ecialization  in  this  creature. 
A  Polyp  is  like  a  colony  of  Amoebae  in  which  some  division  of 
labor  (function)  has  taken  place ;  a  sort  of  biological  state  in 
which  every  individual  is  nearly  equal  to  his  neighbor,  but 
somewhat  more  advanced  than  those  neighbors  not  members  of 
the  organization. 

But  in  one  respect  the  Polyps  show  an  enormous  advance. 
Ordinarily  wlien  nourishment  is  abundant  hydra  multiplies  by 


24 


ANIMAL  PHYSIOLOGY. 


Fig.  43. 


MULTICELLULAR  ORGANISMS.  25 

Figs.  41  to  -16.— In  the  following  figures,  ec,  denotes  ectoderm  ;  en,  endoderm  ;  t,  tentacle  ;  hp, 

hypostome  ;  /.  foot ;  ts,  testes  ;  oi\  ovary  ;  ps.  pseudopodium  ;  ec',  larger  ectoderm-cells ; 

ne\  larger  nematocysts  before  inapture  ;  cp.  Kleiueuberg's  fibers  ;  c.l,  supporting  lamella  ; 

cl,  chloroph.yl-formfng  bodies  ;  c,  cilium 
Fig.  41.— The  greeu  h.ydra,  at  the  maximum  of  contraction  and  elongation  of  its  body.    The 

creature  is  represented  in  the  act  of  seizing  a  small  crustacean  (A,  2). 
Fig.  42.— Transverse  section  across  the  body  of  a  hydra,  in  the  digestive  cavity  of  which  a 

small  crustacean  is  represented. 
Fig.  43. — The  leading  types  of  thread-cells,  after  liberation  from  the  body  (F.  3i.    The  cells  are 

represented  in  the  active  and  the  resting  conditions  ;  in  the  former  all  the  parts  are  more 

distinctly  seen  in  consequence  of  the  necessary  eversion. 
Fig.  44.— Small  portion  of  a  transverse  .section  across  the  body  of  a  green  hydra  (D,  3). 
B^G.  45.— A  large  brown  hydra  bearmg  at  the  same  time  buds  produced  asexually  and  sexual 

organs. 
Fig.  46.— Larger  cells  of  the  ectoderm  isolated.    Note  the  processes  of  the  cells  or  Kleinen- 

berg's  fibers.     (F,  3.) 
AU  of  the  cuts  on  pages,  9,  11,  13,  16,  18,  21  and  24,  have  been  selected  from  Howes'  "Atlas  of 

Biology."' 

budding,  and  when  cut  into  portions  each  may  become  a  com- 
plete individual.  However,  under  other  circumstances,  near 
the  bases  of  the  tentacles  the  body  wall  may  protrude  into  little 
masses  {testes),  in  which  cells  of  peculiar  formation  {sperma- 
tozoa) arise,  and  are  eventually  set  free  and  unite  with  a  cell 
{ovum)  formed  in  a  similar  protrusion  of  larger  size  {ovary). 
Here,  then,  is  the  first  instance  in  which  distinctly  sexual  re- 
production has  been  met  in  our  studies  of  the  lower  forms  of 
life.  This  is  substantially  the  same  process  in  Hydra  as  in 
mammals.  But,  as  both  male  and  female  cells  are  produced  by 
the  same  individual,  the  sexes  are  united  {hermaphroditism) ; 
each  is  at  once  male  and  female. 

Any  one  watching  the  movements  of  a  Polyp,  and  compar- 
ing it  with  those  of  a  Bell-animalcule,  will  observe  that  the 
former  are  much  less  machine-like  ;  have  greater  range ;  seem 
to  be  the  result  of  a  more  deliberate  choice ;  are  better  adapted 
to  the  environment,  and  calculated  to  achieve  higher  ends.  In 
the  absence  of  a  nervous  system  it  is  not  easy  to  explain  how 
one  part  moves  in  harmony  with  another,  except  by  that  process 
which  seems  to  be  of  such  wide  application  in  nature,  adapta- 
tion from  habitual  simultaneous  effects  on  a  protoplasm  capable 
of  responding  to  stimuli.  When  one  process  of  an  Amoeba  is 
touched,  it  is  likely  to  withdraw  all.  This  we  take  to  to  be  due 
to  influences  radiating  through  molecular  movement  to  other 
parts ;  the  same  j>rinciple  of  action  may  be  extended  to  Hydra. 
The  oftener  any  molecular  movement  is  repeated,  the  more  it 
tends  to  become  organized  into  regularity,  to  become  fixed  in 
its  mode  of  action  ;  and  if  we  are  not  mistaken  this  is  a  funda- 
mental law  throughout  the  entire  world  of  living  things,  if  not 
of  all  things  animate  and  inanimate  alike.  To  this  law  we 
shall  return. 

But  Hydra  is  a  creature  of  but  very  limited  specializations; 
there  are  neither  organs  of  circulation,  respiration,  nor  excretion. 


26  ANIMAL  PHYSIOLOGY. 

if  we  exclude  the  doubtful  case  of  tlie  thread-cells  {urticating 
capsules).  The  animal  breathes  by  the  entire  surface  of  the 
body ;  nourishment  passes  from  cell  to  cell,  and  waste  is  dis- 
charged into  the  water  surrounding  the  creature  from  all  cells, 
though  probably  not  quite  equally.  All  parts  are  not  digestive, 
respiratory  etc.,  to  the  same  degree,  and  herein  does  it  differ 
greatly  from  Amoeba  or  even  Vorticella,  though  fuller  knowl- 
edge will  likely  modify  our  views  of  the  latter  two  and  similar 
organisms  in  this  regard. 


THE  CELL  EECONSIDERED, 

Having  now  studied  certain  one-celled  plants  and  animals, 
and  some  very  simple  combinations  of  cells  (molds,  etc.),  it  will 
be  profitable  to  endeavor  to  generalize  the  lessons  these  humble 
organisms  convey ;  for,  as  will  be  constantly  seen  in  the  study 
of  the  higher  forms  of  life  of  which  this  work  proposes  to  treat 
principally,  the  same  laws  operate  as  in  the  lowliest  living 
creatures.  The  most  complex  organism  is  made  up  of  tissues, 
which  are  but  Cells  and  their  products,  as  houses  are  made  of 
bricks,  mortar,  wood,  and  a  few  other  materials,  however  large 
or  elaborate. 

The  student  of  physiology  who  proceeds  scientifically  must 
endeavor,  in  investigating  the  functions  of  each  organ,  to  learn 
the  exact  behavior  of  each  cell  as  determined  by  its  own  inher- 
ent tendencies,  and  modified  by  the  action  of  neighboring  cells. 
The  reason  why  the  function  of  one  organ  differs  from  that  of 
another  is  that  its  cells  have  departed  in  a  special  direction 
from  those  properties  common  to  all  cells,  or  have  become  func- 
tionally differentiated.  But  such  a  statement  has  no  meaning 
unless  it  be  well  understood  that  cells  have  certain  properties  in 
common.  This  is  one  of  the  lessons  imparted  by  the  preceding 
studies  which  we  now  review.  Briefly  stated  in  language  now 
extensively  used  in  works  on  biology,  the  common  properties  of 
cells  (protoplasm),  whether  animal  or  vegetable,  whether  con- 
stituting in  themselves  entire  animals  or  plants,  or  forming  the 
elements  of  tissues,  are  these :  The  collective  chemical  processes 
associated  with  the  vital  activities  of  cells  are  termed  its  meta- 
bolisTTi.  Metabolism  is  constructive  when  more  complex  com- 
pounds are  formed  from  simpler  ones,  as  when  the  Protococcus- 
cell  builds  up  its  protoplasm  out  of  the  simple  materials,  found 
in  rain-water,  which  make  up  its  food.     Metabolism  is  destruct- 


THE  ANIMAL  BODY.  27 

ive  when  the  reverse  process  takes  place.  The  results  of  this 
process  are  eliminated  as  excreta,  or  useless  and  harmful  prod- 
ucts. Since  all  the  vital  activities  of  cells  can  only  be  mani- 
fested when  supplied  with  food,  it  follows  that  living  organisms 
convert  potential  or  possible  energy  into  kinetic  or  actual  en- 
ergy. When  lifeless,  immobile  matter  is  taken  in  as  food  and, 
as  a  result,  is  converted  by  a  process  of  assimilation  into  the 
protoplasm  of  the  cell  using  it,  we  have  an  example  of  poten- 
tial being  converted  into  actual  energy,  for  one  of  the  proper- 
ties of  all  protoplasm  is  its  contractility.  Assimilation  implies, 
of  course,  the  absorption  of  what  is  to  be  used,  with  rejection 
of  waste  matters. 

The  movements  of  protoplasm  of  whatever  kind,  when  due 
to  a  stimulus,  are  said  to  indicate  irritability;  while,  if  inde- 
pendent of  any  external  source  of  excitation,  they  are  denomi- 
nated automatic. 

Among  agents  that  modify  the  action  of  all  kinds  of  proto- 
plasm are  heat,  moisture,  electricity,  light,  and  others  in  great 
variety,  both  chemical  and  mechanical.  It  can  not  be  too  well 
remembered  that  living  things  are  what  they  are,  neither  by 
virtue  of  their  own  organization  alone  nor  through  the  action 
of  their  environment  alone  (else  would  they  be  in  no  sense  dif- 
ferent from  inanimate  things),  but  because  of  the  relation  of 
the  organization  to  the  surroundings. 

Protoplasm,  then,  is  contractile,  irritable,  automatic,  absorp- 
tive, secretory  (and  excretory),  metabolic,  and  reproductive. 

But  when  it  is  affirmed  that  these  are  the  fundamental  prop- 
erties of  all  protoplasm,  the  idea  is  not  to  be  conveyed  that  cells 
exhibiting  these  properties  are  identical  biologically.  No  two 
masses  of  protoplasm  can  be  quite  alike,  else  would  there  be  no 
distinction  in  physiological  demeanor — no  individuality.  Every 
cell,  could  we  but  behold  its  inner  molecular  mechanism,  differs 
from  its  neighbor.  When  this  difference  reaches  a  certain  de- 
gree in  one  direction,  we  have  a  manifest  differentiation  leading 
to  physiological  division  of  labor,  which  may  now  with  advan- 
tage be  treated  in  the  following  section. 


THE  ANIMAL   BODY. 

An  animal,  as  we  have  learned,  may  be  made  up  of  a  single 
cell  in  which  each  part  x>erforms  much  the  same  work  ;  or,  if 
there  be  differences  in  fuii(;ti()n,  they  are  ill-defined  as  compared 


28  ANIMAL  PHYSIOLOGY. 

with  those  of  higher  animals.  The  condition  of  things  in  snch 
an  animal  as  Amoeba  may  be  compared  to  a  civilized  commu- 
nity in  a  very  crude  social  condition.  When  each  individual 
tries  to  perform  every  office  for  himself,  he  is  at  once  carpenter, 
blacksmith,  shoemaker,  and  much  more,  with  the  natural  re- 
sult that  he  is  not  efficient  in  any  one  direction.  A  community 
may  be  judged  in  regard  to  its  degree  of  advancement  by  the 
amount  of  division  of  labor  existing  within  it.  Thus  is  it  with 
the  animal  body.  We  find  in  such  a  creature  as  the  fresh-water 
Hydra,  consisting  of  two  layers  of  cells  forming  a  simple  sac,  a 
slight  amount  of  advancement  on  Amoeba.  Its  external  surface 
no  longer  serves  for  inclosure  of  food,  but  it  has  the  simplest 
form  of  mouth  and  tentacles.  Each  of  the  cells  of  the  internal 
layer  seems  to  act  as  a  somewhat  improved  or  specialized  Amoe- 
ba, while  in  those  of  the  outer  layer  we  mark  a  beginning  of 
those  functions  which  taken  collectively  give  the  higher  ani- 
mals information  of  the  surrounding  world. 

Looking  to  the  existing  state  of  things  in  the  universe,  it  is 
I  plain  that  an  animal  to  attain  to  high  ends  must  have  powers 
of  rapid  locomotion,  capacity  to  perceive  what  makes  for  its  in- 
terest, and  ability  to  utilize  means  to  attain  this  when  perceived. 
These  considerations  demand  that  an  animal  high  in  the  scale 
of  being  should  be  provided  with  limbs  sufficiently  rigid  to  sup- 
port its  weight,  moved  by  strong  muscles,  which  must  act  in 
harmony.  But  this  implies  abundance  of  nutriment  duly  pre- 
pared and  regularly  conveyed  to  the  bones  and  muscles.  All 
this  would  be  useless  unless  there  was  a  controlling  and  ener- 
gizing system  capable  both  of  being  impressed  and  originating 
impressions.  Such  is  found  in  the  nerves  and  nerve-centers. 
Again,  in  order  that  this  mechanism  be  kept  in  good  running 
order,  the  waste  of  its  own  metabolism,  which  chokes  and  poi- 
sons, must  be  got  rid  of — hence  the  need  of  excretory  apparatus. 
In  order  that  the  nervous  system  may  get  sufficient  informa- 
tion of  the  world  around,  the  surface  of  the  body  must  be  pro- 
vided with  special  message-receiving  offices  in  the  form  of 
modified  nerve-endings.  In  short,  it  is  seen  that  an  animal  as 
high  in  the  scale  as  a  mammal  must  have  muscular,  osseous 
(and  connective),  digestive,  circulatory,  excretory,  and  nervous 
tissues  ;  and  to  these  may  be  added  certain  forms  of  protective 
tissues,  as  hair,  nails,  etc. 

Assuming  that  the  student  has  at  least  some  general  knowl- 
edge of  the  structure  of  these  various  tissues,  we  propose  to  tell 
in  a  simple  way  the  whole  physiological  story  in  brief. 


THE  ANIMAL  BODY.  29 

The  blood  is  the  source  of  all  the  nourishment  of  the  organ- 
ism, including  its  oxygen  supply,  and  is  carried  to  every  j^art  of 
the  body  through  elastic  tubes  which,  continually  branching 
and  becoming  gradually  smaller,  terminate  in  vessels  of  hair- 
like fineness  in  which  the  current  is  very  slow — a  condition  per- 
m.itting  that  interchange  between  the  cells  surrounding  them 
and  the  blood  which  may  be  compared  to  a  process  of  barter, 
the  cells  taking  nutriment  and  oxygen,  and  giving  (excreting) 
in  return  carbonic  anhydride.  From  these  minute  vessels  the 
blood  is  conveyed  back  toward  the  source  whence  it  came  by 
similar  elastic  tubes  which  gradually  increase  in  size  and  be- 
come fewer.  The  force  which  directly  propels  the  blood  in  its 
onward  course  is  a  muscular  pump,  with  both  a  forcing  and 
suction  action,  though  chiefly  the  former.  The  flow  of  blood 
is  maintained  constant  owing  to  the  resistance  in  the  smaller 
tubes  on  the  one  hand  and  the  elastic  recoil  of  the  larger  tubes 
on  the  other;  while  in  the  returning  vessels  the  column  of 
blood  is  supported  by  elastic  double  gates  which  so  close  as  to 
prevent  reflux.  The  oxygen  of  the  blood  is  carried  in  disks  of 
microscopic  size  which  give  it  up  in  proportion  to  the  needs  of 
the  tissues  past  which  they  are  carried. 

But  in  reality  the  tissues  of  the  body  are  not  nourished 
directly  by  the  blood,  but  by  a  fluid  derived  from  it  and  resem- 
bling it  greatly  in  most  particulars.  This  fluid  bathes  the 
tissue-cells  on  all  sides.  It  also  is  taken  up  by  tubes  that 
convey  it  into  the  blood  after  it  has  passed  through  little  fac- 
tories (lymphatic  glands),  in  which  it  undergoes  a  regeneration. 
Since  the  tissues  are  impoverishing  the  blood  by  withdrawal  of 
its  constituents,  and  adding  to  it  what  is  no  longer  useful,  and 
is  in  reality  poisonous,  it  becomes  necessary  that  new  material 
be  added  to  it  and  the  injurious  components  withdrawn.  The 
former  is  accomplished  by  the  absorption  of  the  products  of 
food  digestion,  and  the  addition  of  a  fresh  supply  of  oxygen 
derived  from  without,  while  the  poisonous  ingredients  that 
have  found  their  way  into  the  blood  are  got  rid  of  through 
processes  that  may  be,  in  general,  compared  to  those  of  a  sew- 
age system  of  a  very  elaborate  character.  To  explain  this  re- 
generation of  the  blood  in  somewhat  more  detail,  we  must  first 
consider  the  fate  of  food  from  the  time  it  enters  the  moutli  till 
it  leaves  the  tract  of  the  body  in  which  its  preparation  is 
carried  on. 

The  food  is  in  the  mouth  submitted  to  the  action  of  a  series 
of  cutting  and  grinding  organs  worked  by  powerful  muscles ; 


30  ANIMAL  PHYSIOLOGY. 

mixed  with  a  fluid  wliich  changes  the  starchy  part  of  it  into 
sugar,  and  prepares  the  whole  to  pass  further  on  its  course : 
when  this  has  been  accomplished,  the  food  is  grasped  and 
squeezed  and  pushed  along  the  tube,  owing  to  the  action  of  its 
own  muscular  cells,  into  a  sac  (stomach),  in  which  it  is  rolled 
about  and  mixed  with  certain  fluids, of  peculiar  chemical  com- 
position derived  from  cells  on  its  inner  surface,  which  trans- 
form the  proteid  part  of  the  food  into  a  form  susceptible  of 
ready  use  (absorption).  When  this  saccular  organ  has  done 
its  share  of  the  work,  the  food  is  moved  on  by  the  action  of 
the  muscles  of  its  walls  into  a  very  long  portion  of  the  tract  in 
which,  in  addition  to  processes  carried  on  in  the  mouth  and 
stomach,  there  are  others  which  transform  the  food  into  a 
condition  in  which  it  can  pass  into  the  blood.  Thus,  all  of 
the  food  that  is  susceptible  of  changes  of  the  kind  described  is 
acted  upon  somewhere  in  the  long  tract  devoted  to  this  task. 
But  there  is  usually  a  remnant  of  indigestible  material  which 
is  finally  evacuated.  How  is  the  prepared  material  conveyed 
into  the  blood  ?  In  part,  directly  through  the  walls  of  the 
minutest  blood-vessels  distributed  throughout  the  length  of 
this  tube ;  and  in  part  through  special  vessels  with  appropriate 
cells  covering  them  which  act  as  minute  porters  {villi). 

The  impure  blood  is  carried  periodically  to  an  extensive  sur- 
face, usually  much  folded,  and  there  exposed  in  the  hair-like 
tubes  referred  to  before,  and  thus  parts  with  its  excess  of  car- 
bon dioxide  and  takes  up  fresh  oxygen.  But  all  the  functions 
described  do  not  go  on  in  a  fixed  and  invariable  manner,  but 
are  modified  somewhat  according  to  circumstances.  The  for- 
cing-pump of  the  circulatory  system  does  not  always  beat 
equally  fast;  the  smaller  blood-vessels  are  not  always  of  the 
same  size,  but  admit  more  or  less  blood  to  an  organ  according 
to  its  needs. 

This  is  all  accomplished  in  obedience  to  the  commands  car- 
ried from  the  brain  and  spinal  cord  along  the  nerves.  All 
movements  of  the  limbs  and  other  parts  are  executed  in  obe- 
dience to  its  behests ;  and  in  order  that  these  may  be  in  accord- 
ance with  the  best  interests  of  each  particular  organ  and  the 
whole  animal,  the  nervous  centers,  which  may  be  compared  to 
the  chief  officers  of,  say,  a  telegraph  or  railway  system,  are  in 
constant  receipt  of  information  by  messages  carried  onward 
along  the  nerves.  The  command  issuing  is  always  related  to 
the  information  arriving. 

All  those  parts  commonly  known  as  sense-organs — the  eye, 


LIVING   AND  LIFELESS  MATTER.  31 

ear,  nose,  tongue,  and  the  entire  surface  of  the  body — are  faith- 
ful reporters  of  facts.  They  put  the  inner  and  outer  worlds  in 
communication,  and  without  them  all  higher  life  at  least  must 
cease,  for  the  organism,  like  a  train  directed  by  a  conductor  that 
disregards  the  danger-signals,  must  work  its  own  destruction. 
Without  going  into  further  details,  suffice  it  to  say  that  the  pro- 
cesses of  the  various  cells  are  subordinated  to  the  general  good 
through  the  nervous  system,  and  that  susceptibility  of  proto- 
jDlasm  to  stimuli  of  a  delicate  kind  which  enables  each  cell  to 
adapt  to  its  surroundings,  including  the  influence  of  remote  as 
well  as  neighboring  cells.  Without  this  there  could  be  no 
marked  advance  in  organisms,  no  differentiation  of  a  pro- 
nounced character,  and  so  none  of  that  physiological  division 
of  labor  which  will  be  inferred  from  our  brief  description  of 
the  functions  of  a  mammal.  The  whole  of  physiology  but 
illustrates  this  division  of  labor. 

It  is  hoped  that  the  above  account  of  the  working  of  the 
animal  body,  brief  as  it  is,  may  serve  to  show  the  connection  of 
one  part  functionally  with  another,  for  it  is  much  more  impor- 
tant that  this  should  be  kept  in  mind  throughout,  than  that  all 
the  details  of  any  one  function  should  be  known. 


LIVING  AND  LIFELESS  MATTER. 

In  order  to  enable  the  student  the  better  to  realize  the  na- 
ture of  living  matter  or  protoplasm,  and  to  render  clearer 
the  distinction  between  the  forms  that  belong  to  the  organic 
and  inorganic  worlds  respectively,  we  shall  make  some  com- 
parisons in  detail  which  it  is  hoped  may  accomplish  this  ob- 
ject. 

A  modern  watch  that  keeps  correct  time  must  be  regarded 
as  a  wonderful  object,  a  marvelous  triumph  of  human  skill. 
That  it  has  aroused  the  awe  of  savages,  and  been  mistaken  for 
a  living  being,  is  not  surprising.  But,  admirable  as  is  the 
result  attained  by  the  mechanism  of  a  watch,  it  is,  after  all, 
composed  of  but  a  few  metals,  etc.,  chiefly  in  fact  of  two,  brass 
and  steel ;  these  are,  however,  made  up  into  a  great  number 
of  different  parts,  so  adapted  to  one  another  as  to  work  in 
unison  and  accomplish  the  desired  object  of  indicating  the  time 
of  day. 

Now,  however  well  constructed  the  watch  may  be,  there  are 
waste,  wear  and  tear,  which  will  manifest  themselves  more  and 


32  ANIMAL   PHYSIOLOGY. 

more,  until  finally  tlie  machine  becomes  worthless  for  the  pur- 
pose of  its  construction.  If  this  mechanism  possessed  the 
power  of  adapting  from  without  foreign  matter  so  as  to  con- 
struct it  into  steel  and  hrass  and  arrange  this  just  when  re- 
quired, it  would  imitate  a  living  organism ;  but  this  it  can  not 
do,  nor  is  its  waste  chemically  different  from  its  component 
metals ;  it  does  not  break  up  brass  and  steel  into  something 
wholly  different.  In  one  particular  it  does  closely  resemble 
living  things,  in  that  it  gradually  deteriorates ;  but  the  degra- 
dation of  a  living  cell  is  the  consequence  of  an  actual  change 
in  its  component  parts,  commonly  a  fatty  degeneration.  The 
one  is  a  real  transformation,  the  other  mere  wear. 

Had  the  watch  the  power  to  give  rise  to  a  new  one  like  itself 
by  any  process,  especially  a  process  of  division  of  itself  into  two 
parts,  we  should  have  a  parallel  with  living  forms ;  but  the 
watch  can  not  even  renew  its  own  parts,  much  less  give  rise  to 
a  second  mechanism  like  itself.  Here,  then,  is  a  manifest  dis- 
tinction between  living  and  inanimate  things. 

Suppose  further  that  the  watch  was  so  constructed  that, 
after  the  lapse  of  a  certain  time,  it  underwent  a  change  in  its 
inner  machinery  and  perhaps  its  outer  form,  so  as  to  be  scarcely 
recognizable  as  the  same ;  and  that  as  a  result,  instead  of  indi- 
cating the  hours  and  minutes  of  a  time-reckoning  adapted  to 
the  inhabitants  of  our  globe,  it  indicated  time  in  a  wholly  dif- 
ferent way ;  that  after  a  series  of  such  transformations  it  fell  to 
pieces — took  the  original  form  of  the  metals  from  which  it 
was  constructed — we  should  then  have  in  this  succession  of 
events  a  parallel  with  the  development,  decline,  and  death  of 
living  organisms. 

In  another  particular  our  illustration  of  a  watch  may  serve 
a  useful  purpose.  Suppose  a  watch  to  exist,  the  works  of  which 
are  so  concealed  as  to  be  quite  inaccessible  to  our  vision,  so  that 
all  we  know  of  it  is  that  it  has  a  mechanism  which  when  in 
action  we  can  hear,  and  the  result  of  which  we  perceive  in  the 
movements  of  the  hands  on  the  face ;  we  should  then  be  in  the 
exact  position  in  reference  to  the  watch  that  we  now  are  as  re- 
gards the  molecular  movements  of  protoplasm.  On  the  latter 
the  entire  behavior  of  living  matter  depends ;  yet  it  is  abso- 
lutely hidden  from  us. 

We  know,  too,  that  variations  must  be  produced  iu  the 
mechanism  of  time-pieces  by  temperature,  moisture,  and  other 
influences  of  the  environment,  resulting  in  altered  action.  The 
same,  as  will  be  shown  in  later  chapters,  occurs  in  protoplasm. 


CLASSIFICATION   OF  THE  ANIMAL   KINGDOM.  33 

This,  too,  is  primarily  a  molecular  effect.  If  the  works  of 
watches  were  beyond  observation,  we  should  not  be  able  to  state 
exactly  how  the  variations  observed  in  different  kinds,  or  even 
different  individuals  of  the  same  kind  occurred,  though  these 
differences  might  be  of  the  most  marked  character,  such  as  any 
one  could  recognize.  Here  once  more  we  refer  the  differences 
to  the  mechanism.  So  is  it  with  living  beings:  the  ultimate 
molecular  mechanism  is  unknown  to  us. 

Could  we  but  render  these  molecular  movements  visible  to 
our  eyes,  we  should  have  a  revelation  of  far  greater  scientific 
importance  than  that  unfolded  by  the  recent  researches  into 
those  living  forms  of  extreme  minuteness  that  swarm  every- 
where as  dust  in  a  sunbeam,  and,  as  will  be  learned  later,  are 
often  the  source  of  deadly  disease.  Like  the  movements  of  the 
watch,  the  activities  of  protoplasm  are  ceaseless.  A  watch  that 
will  not  run  is,  as  such,  worthless — it  is  mere  metal — has  under- 
gone an  immense  degradation  in  the  scale  of  values;  so  proto- 
plasm is  no  longer  protoplasm  when  its  peculiar  molecular 
movements  cease ;  it  is  at  once  degraded  to  the  rank  of  dead 
matter. 

The  student  may  observe  that  each  of  the  four  propositions, 
embodying  the  fundamental  properties  of  living  matter,  stated 
in  the  preceding  chapter,  have  been  illustrated  by  the  simile  of 
a  watch.  Such  an  illustration  is  necessarily  crude,  but  it  helps 
one  to  realize  the  meaning  of  truths  which  gather  force  with 
each  living  form  studied  if  regarded  aright ;  and  it  is  upon  the 
realization  of  truth  that  mental  growth  as  well  as  practical 
efficiency  depends. 


CLASSIFICATION  OF  THE  ANIMAL   KINGDOM. 

There  are  human  beings  so  low  in  the  scale  as  not  to  possess 
such  general  terms  as  tree,  while  they  do  employ  names  for  dif- 
ferent kinds  of  trees.  The  use  of  such  a  word  as  "  tree "  im- 
]jlies  generalization,  or  the  abstraction  of  a  set  of  qualities  from 
the  tilings  in  which  they  reside,  and  making  them  the  basis  for 
the  grouping  of  a  multitude  of  objects  by  which  we  are  sur- 
rounded. Manifestly  without  such  a  jjrocess  knowledge  must 
be  vfry  limited,  and  the  world  without  significance;  while  in 
proportion  as  generalization  may  be  safely  widened,  is  our 
progress  in  the  unification  of  knowledge  toward  which  science 
is  tending.     But  it  also  follow.s  that  without  complete  knowl- 

8 


34  ANIMAL  PHYSIOLOGY. 

edge  there  can  be  no  perfect  classification  of  objects;  hence, 
any  classification  must  be  regarded  but  as  the  temporary  creed 
of  science,  to  be  modified  with  the  extension  of  knowledge.  As 
a  matter  of  fact,  this  has  been  the  history  of  all  zoological  and 
other  systems  of  arrangement.  The  only  purpose  of  grouping 
is  to  simplify  and  extend  knowledge ;  this  being  the  case,  it  fol- 
lows that  a  method  of  grouping  that  accomplishes  this  has 
value,  though  the  system  may  be  artificial  that  is  based  on 
resemblances  which,  though  real  and  constant,  are  associated 
with  differences  so  numerous  and  radical  that  the  total  amount 
of  likeness  between  objects  thus  grouped  is  often  less  than  the 
difference.  Such  a  system  was  that  of  Linnaeus,  who  classified 
plants  according  to  the  number  of  stamens,  etc.,  they  bore. 

Seeing  that  animals  which  resemble  each  other  are  of  com- 
mon descent  from  some  earlier  form,  to  establish  the  line  of  de- 
scent is  to  determine  in  great  part  the  classification.  Much  as- 
sistance in  this  direction  is  derived  from  embryology,  or  the 
history  of  the  development  of  the  individual  ( ontogeny) ;  so 
that  it  may  be  said  that  the  ontogeny  indicates,  though  it  does 
not  actually  determine,  the  line  of  descent  (phylogeny)  ;  and  it 
is  owing  to  the  importance  of  this  truth  that  naturalists  have 
in  recent  years  given  so  much  attention  to  comparative  embry- 
ology. 

It  will  be  inferred  that  a  natural  system  of  classification  must 
be  based  both  on  function  and  structure,  though  chiefly  on  the 
latter,  since  organs  of  very  different  origin  may  have  a  similar 
function ;  or,  to  express  this  otherwise,  homologous  structures 
may  not  be  analogous  ;  and  homology  gives  the  better  basis  for 
classification.  To  illustrate,  the  wing  of  a  bat  and  a  bird  are 
both  homologous  and  analogous;  the  wing  of  a  butterfly  is 
analogous  but  not  homologous  with  these  ;  manifestly,  to  clas- 
sify bats  and  birds  together  would  be  better  than  to  put  birds 
and  insects  in  the  same  group,  thus  leaving  other  points  of  re- 
lationship out  of  consideration. 

The  broadest  possible  division  of  the  animal  kingdom  is  into 
groups,  including  respectively  one-celled  and  many-celled 
forms — i.  e.,  into  Protozoa  and  Metazoa.  As  the  wider  the 
grouping  the  less  are  differences  considered,  it  follows  that  the 
more  subdivided  the  groups  the  more  complete  is  the  informa- 
tion conveyed :  thus,  to  say  that  a  dog  is  a  metazoan  is  to  con- 
vey a  certain  amount  of  information ;  that  it  is  a  vertebrate, 
more ;  that  it  is  a  mammal,  a  good  deal  more,  because  each  of 
the  latter  terms  includes  the  former. 


Animal 
Kiug- 
dom. 


CLASSIFICATION  OF  THE  ANIMAL  KINGDOM.  35 

f  Protozoa  (amoeba,  vorticella,  etc.). 
j  Coelenterata  (sponges,  jelly-fish,  jjolyps,  etc.). 
I  Echinodermata  (star-fish,  sea-urchins,  etc.). 
r      Inverte-      J  Vermes  (worms). 

brata.         ]  Arthropods  (crabs,  insects,  spiders,  etc.). 
Mollusca  (oysters,  snails,  etc.). 
Molluscoidea  (moss-like  animals). 
[  Tunicata  (ascidians). 

f  Pisces  (fishes). 

I  Amphibia  (frogs,  menobranchus,  etc.). 
t  Vertebrata.    -J  Keptilia  (snakes,  turtles,  etc.). 
I  Aves  (birds). 
[  Mammalia  (domestic  quadrupeds,  etc.). 

The  above  classification  (of  Claus)  is,  like  all  such  arrange- 
ments, but  the  expression  of  one  out  of  many  methods  of  view- 
ing the  animal  kingdom. 

For  the  details  of  classification  and  for  the  grounds  of  that 
we  have  presented,  we  refer  the  student  to  works  on  zoology ; 
but  we  advise  those  who  are  not  familiar  with  this  subject, 
when  a  technical  term  is  used,  to  think  of  that  animal  belong- 
ing to  the  group  in  question  with  the  structure  of  which  they 
are  best  acquainted. 

Man's  Place  in  the  Animal  Kingdom. 

It  is  no  longer  the  custom  with  zoologists  to  place  man  in 
an  entirely  separate  group  by  himself ;  but  he  is  classed  with 
the  primates,  among  which  are  also  grouped  the  anthropoid 
apes  (gorilla,  chimpanzee,  orang,  and  the  gibbon),  the  monkeys 
of  the  Old  and  of  the  New  World,  and  the  lemurs.  So  great  is 
the  structural  resemblance  of  man  and  the  other  primates  that 
competent  authorities  declare  that  there  is  more  difference  be- 
tween the  structure  of  the  most  widely  separated  members  of 
the  group  than  between  certain  of  the  anthr(^poid  apes  and  man. 

The  points  of  greatest  resemblance  between  man  and  the 
anthropoid  apes  are  the  following :  The  same  number  of  verte- 
bree  ;  the  same  general  shape  of  the  pelvis ;  a  brain  distinguish- 
ing them  from  other  mammals;  and  posture,  being  bipeds. 

The  distinctive  characters  are  size,  rather  than  form  of  the 
brain,  that  of  man  being  more  than  twice  as  large ;  a  relatively 
larger  cranial  base,  by  which,  together  with  the  greater  size  of 
the  jaw.s,  the  face  becomes  prominent ;  the  earlier  closure  of 
the  sutures  of  the  cranium,  arresting  the  growth  of  the  brain ; 
more  developed  canine  teeth  and  difference  in  the  order  of 
eruption  of  the  permanent  teeth ;  the  more  i)osterior  position 
of  the  foramen  magnum ;  the  relative  length  of  the  limbs  to 


36 


ANIMAL  PHYSIOLOGY. 


each  other  and  the  rest  of  the  body ;  minor  differences  in  the 
hands  and  feet,  especially  the  greater  freedom  and  power  of 
apposition  of  the  great-toe. 

But  the  greatest  distinction  between  man  and  even  his 
closest  allies  among  the  apes  is  to  be  found  in  the  development 
to  an  incomparably  higher  degree  of  his  intellectual  and  moral 
nature,  corresponding  to  the  differences  in  weight  and  structure 
of  the  human  brain,  and  associated  with  the  use  of  spoken  and 
written  language ;  so  that  the  experience  of  previous  genera- 
tions is  not  only  registered  in  the  organism  (heredity),  but  in  a 
form  more  quickly  available  (books,  etc.). 

The  greatest  structural  difference  between  the  races  of  men 
are  referable  to  the  cranium;  but,  since  they  all  interbreed 
freely,  they  are  to  be  considered  varieties  of  one  species. 


THE  LAW  OP  PERIODICITY  OR  RHYTHM  IN  NATURE. 

The  term  rhythm  to  most  minds  suggests  music,  poetry,  or 
dancing,  in  all  of  which  it  forms  an  essential  part  so  simple, 
pronounced,  and  uncomplicated  as  to  be  recognized  by  all  with 
ease. 

The  regular  division  of  music  into  bars,  the  recurrence  of 
chords  of  the  same  notes  at  certain  intervals,  of  forte  and  piano, 
seem  to  be  demanded  by  the  very  nature  of  the  human  mind. 
The  same  applies  to  poetry.  Even  a  child  that  can  not  under- 
stand the  language  used,  or  an  adult  listening  to  recitations  in 
an  unknown  tongue,  enjoys  the  flow  and  recurrences  of  the 
sounds.  Dancing  has  in  all  ages  met  a  want  in  human  organi- 
zations, which  is  partly  supplied  in  quieter  moods  by  the  regu- 
larity of  the  steps  in  walking  and  similar  simple  movements. 

But  as  rhythm  runs  through  all  the  movements  of  animals, 
so  is  it  also  found  in  all  literature  and  all  art.  Infinite  variety 
wearies  the  mind,  hence  the  fatigue  felt  by  the  sight-seer.  Re- 
currence permits  of  repose,  and  gratifies  an  established  taste  or 
appetite.  The  mind  delights  in  what  it  has  once  enjoyed,  in 
repetition  within  limits.  Repetition  with  variety  is  manifestly 
a  condition  of  the  growth  and  development  of  the  mind.  This 
seems  to  apply  equally  to  the  body,  for  every  single  function 
of  each  organism,  however  simple  or  complex  it  may  be,  exem- 
plifies this  law  of  periodicity.  The  heart's  action  is  rhythmical 
(beats) ;  the  blood  flows  in  intermitting  gushes  from  the  central 
pump ;  the  to-and-fro  movements  of  respiration  are  so  regular 


THE  LAW  OF  PERIODICITY   OR  RHYTHM   IN   NATURE.       37 

that  their  cessation  would  arouse  the  attention  of  the  least 
instructed ;  food  is  demanded  at  regular  intervals ;  the  juices 
of  the  digestive  tract  are  poured  out,  not  constantly  but  period- 
ically ;  the  movements  by  which  the  food  is  urged  along  its 
path  are  markedly  rhythmic ;  the  chemical  processes  of  the 
body  wax  and  wane  like  the  fires  in  a  furnace,  giving  rise  to 
regular  augmentations  of  the  temperature  of  the  body  at  fixed 
hours  of  the  day,  with  corresponding  periods  of  greatest  bodily 
activity  and  the  reverse. 

This  principle  finds  perfect  illustration  in  the  nervous  sys- 
tem. The  respiratory  act  of  the  higher  animals  is  efi:ected 
through  muscular  movements  dependent  on  regular  waves  of 
excitation  reaching  them  along  the  nerves  from  the  central  cells 
which  regularly  discharge  their  forces  along  these  channels. 
Were  not  the  movements  of  the  body  periodic  or  rhythmical, 
instead  of  that  harmony  which  now  prevails,  every  muscular 
act  would  be  a  convulsion,  though  even  in  the  movements  of 
the  latter  there  is  a  highly  compounded  rhythm,  as  a  noise  is 
made  up  of  a  variety  of  musical  notes.  The  senses  are  subject 
to  the  same  law.  The  eye  ceases  to  see  and  the  ear  to  hear  and 
the  hand  to  feel  if  continuously  stimulated ;  and  doubtless  in 
all  art  this  law  is  unconsciously  recognized.  That  ceases  to  be 
art  which  fails  to  provide  for  the  alternate  repose  and  excita- 
tion of  the  senses.  The  eye  will  not  tolerate  continuously  one 
color,  the  ear  a  single  sound.  Why  is  a  breeze  on  a  warm  day 
so  refreshing  ?     The  answer  is  obvious. 

Looking  to  the  world  of  animate  nature  as  a  whole,  it  is 
noticed  that  i)lants  have  their  period  of  sprouting,  flowering, 
seeding,  and  decline ;  animals  are  born,  pass  through  various 
stages  to  maturity,  diminish  in  vigor,  and  die.  These  events 
make  epochs  in  the  life-history  of  each  species  ;  the  recurrence 
of  which  is  so  constant  that  the  agricultural  and  other  arrange- 
ments even  of  savages  are  planned  accordingly.  That  the  in- 
dividuals of  each  animal  group  have  a  definite  period  of  dura- 
tion is  another  manifestation  of  the  same  law. 

Superficial  observation  suffices  to  furnish  facts  which  show 
that  the  same  law  of  periodicity  is  being  constantly  exemplified 
in  the  world  of  inanimate  things.  The  regular  ebb  and  flow  of 
the  tides ;  the  rise  and  suT)sidence  of  rivers  ;  the  storm  and  the 
calm;  summer  and  winter;  day  and  night — are  all  recurrent, 
none  constant. 

Events  apparently  without  any  regularity,  utterly  l)eyond 
any  law  of  recurrence,  when  sufficiently  studied  are  found  to 


38 


ANIMAL  PHYSIOLOGY. 


fall  under  the  same  principle.  Thus  it  took  some  time  to  learn 
that  volcanic  eruptions  occurred  with  a  very  fair  degree  of 
regularity. 

In  judging  of  this  and  all  other  rhythmical  events  it  must 
be  borne  in  mind  that  the  time  standard  is  for  an  irregularity 
that  seems  large,  as  in  the  instance  just  referred  to,  becomes 
small  when  considered  in  relation  to  the  millions  of  years  of 
geological  time ;  while  in  the  case  of  music  a  trifling  irregu- 
larity, judged  by  fractions  of  a  second,  can  not  be  tolerated 
by  the  musical  organization— which  is  equivalent  to  saying 
that  the  interval  of  departure  from  exact  regularity  seems 
large. 

As  most  of  the  rhythms  of  the  universe  are  compounded  of 
several,  it  follows  that  they  may  seem,  until  closely  studied, 
very  far  from  regular  recurrences.  This  may  be  observed  in 
the  interference  in  the  regularity  of  the  tides  themselves,  the 
daily  changes  of  which  are  subject  to  an  increase  and  decrease 
twice  in  each  month,  owing  to  the  influence  of  the  sun  and  moon 
being  then  either  coincident  or  antagonistic. 

In  the  functions  of  plants  and  animals,  rhythms  must  be- 
come very  greatly  compounded,  doubtless  often  beyond  recog- 
nition. 

Among  the  best  examples  of  rhythm  in  animals  are  daily 
sleep  and  winter  sleep,  or  hibernation  ;  yet,  amid  sleep,  dreams 
or  recurrences  of  cerebral  activity  are  common — that  is,  one 
rhythm  (of  activity)  overlies  another  (of  repose).  In  like  man- 
ner many  hibernating  animals  do  not  remain  constantly  in  their 
dormant  condition  throughout  the  winter  months,  but  have 
periods  of  wakefulness ;  the  active  life  recurs  amid  the  life  of 
functional  repose. 

To  return  to  the  world  of  inanimate  matter,  we  find  that  the 
crust  of  the  earth  itself  is  made  of  layers  or  strata  the  result  of 
periods  of  elevation  and  depression,  of  denudation  and  deposi- 
tion, in  recurring  order. 

The  same  law  is  illustrated  by  the  facts  of  the  economic  and 
other  conditions  of  the  social  state  of  civilized  men.  Periods 
of  depression  alternate  with  periods  of  revival  in  commercial 
life. 

There  are  periods  when  many  more  marriages  occur  and 
many  more  children  are  born,  corresponding  with  changes  in 
the  material  conditions  which  influence  men  as  well  as  other 
animals. 

Finally,  and  of  special  interest  to  the  medical  student,  are 


THE  LxVW  OF   PERIODICITY  OR  RHYTHM   IN  NATURE.       39 

the  laws  of  rhythm  in  disease.  Certain  fevers  have  their  regu- 
lar periods  of  attack,  as  intermittent  fever ;  while  all  diseases 
have  their  periods  of  exacerbation,  however  invariable  the 
symptoms  may  seem  to  be  to  the  ordinary  observer  or  even  to 
the  patient  himself. 

Doubtless  the  fact  that  certain  hereditary  diseases  do  not 
appear  in  the  offspring  at  once,  but  only  at  the  age  at  which 
they  were  manifested  in  the  parents,  is  owing  to  the  same 
cause. 

Let  us  now  examine  more  thoroughly  into  the  real  nature  of 
this  rhythm  which  pervades  the  entire  universe. 

If  a  bow  be  drawn  across  a  violin-string  on  which  some  small 
pieces  of  paper  have  been  placed,  these  will  be  seen  to  fly  off ; 
and  if  the  largest  string  be  experimented  upon,  it  can  be  ob- 
served to  be  in  rapid  to-and-fro  motion,  known  as  vibration, 
which  motion  is  perfectly  regular,  a  definite  number  of  move- 
ments occurring  within  a  measured  period  of  time ;  in  other 
words  the  motion  is  rhythmical.  In  strings  of  the  finest  size 
the  motion  is  not  visible,  but  we  judge  of  its  existence  because 
of  the  result,  which  is  in  each  instance  a  sound.  Sound  is  to  us, 
however,  an  affection  of  the  nerve  of  hearing  and  the  brain, 
owing  to  the  vibrations  of  the  ear  caused  by  similar  vibra- 
tions of  the  violin-strings.  The  movements  of  the  nerves  and 
nerve-cells  are  invisible  and  molecular,  and  we  seem  to  be 
justified  in  regarding  molecular  movements  as  constant  and 
associated  with  all  the  properties  of  matter  ivhether  living  or 
dead. 

We  see,  then,  that  all  things  living  and  lifeless  are  in  con- 
stant motion,  visible  or  invisible ;  there  is  no  such  thing  in  the 
universe  as  stable  equilibrium.  Change,  ceaseless  change,  is 
written  on  all  things;  and,  so  far  as  we  can  judge,  these 
changes,  on  the  whole,  tend  to  higher  development.  Neither 
rhythm,  however,  nor  anything  else,  is  perfect.  Even  the  mo- 
tions of  jjlanets  are  subject  to  perturbations  or  irregularities 
in  their  periodicity.  This  subject  is  plainly  boundless  in  its 
scope.  We  have  introduced  it  at  this  stage  to  prepare  for  its 
study  in  detail  in  dealing  with  each  function  of  the  animal 
body.  If  we  are  correct  as  to  the  universality  of  the  law  of 
rhythm,  its  importance  in  biology  deserves  fuller  recognition 
than  it  has  yet  received  in  works  on  physiology ;  it  will,  ac- 
cordingly, be  frequently  referred  to  in  the  future  chapters  of 
this  book. 


40  ANIMAL   PHYSIOLOGY. 


THE  LAW  OF  HABIT. 

Every  one  must  have  observed  in  himself  and  others  the 
tendency  to  fall  into  set  ways  of  doing  certain  things,  in  which 
will  and  clear  purpose  do  not  come  prominently  into  view. 
Further  observation  shows  that  the  lower  animals  exhibit  this 
tendency,  so  that,  for  example,  the  habits  of  the  horse  or  the  dog 
may  be  an  amusing  reflection  of  those  of  the  master.  Trees  are 
seen  to  bend  permanently  in  the  direction  toward  which  the 
prevailing  winds  blow. 

The  violin  that  has  experienced  the  vibrations  aroused  by 
some  master's  hand  acquires  a  potential  musical  capability  not 
possessed  by  an  instrument  equally  good  originally,  but  the 
molecular  movements  of  which  never  received  such  an  educa- 
tion. 

It  appears,  then,  that  underlying  what  we  call  habit,  there  is 
some  broad  law  not  confined  to  living  things ;  indeed,  the  law  of 
habit  appears  to  be  closely  related  to  the  law  of  rhythm  we 
have  already  noticed.  Certain  it  is  that  it  is  inseparable  from 
all  biological  phenomena,  though  most  manifest  in  those  organ- 
isms provided  with  a  nervous  system,  and  in  that  system  itself. 
What  we  usually  call  habit,  however  expressed,  has  its  physical 
correlation  in  the  nervous  system.  We  may  refer  to  it  in  this 
connection  later :  but  the  subject  has  relations  so  numerous  and 
fundamental  that  it  seems  eminently  proper  to  introduce  it  at 
this  early  stage,  forming  as  it  does  one  of  those  corner-stones  of 
the  biological  building  on  which  the  superstructure  must  rest. 

When  we  seek  to  come  to  a  final  explanation  of  habit  in  this 
case,  as  in  most  others,  in  which  the  fundamental  is  involved, 
we  are  soon  brought  against  a  wall  over  which  we  are  unable 
to  climb,  and  through  which  no  light  comes  to  our  intellects. 

We  must  simply  believe,  as  the  result  of  observation,  that  it 
is  a  law  of  matter,  in  all  the  forms  manifested  to  us,  to  assume 
accustomed  modes  of  behavior,  perhaps  we  may  say  molecular 
movement,  in  obedience  to  inherent  tendencies.  But,  to  recog- 
nize this,  throws  a  flood  of  light  on  what  would  be  inexplicable, 
even  in  a  minor  degree.  We  can  not  explain  gravitation  in  it- 
self ;  but,  assuming  its  universality,  replaces  chaos  by  order  in 
our  speculations  on  matter. 

Turning  to  living  matter,  we  look  for  the  origin  of  habit  in 
the  apparently  universal  principle  that  primary  molecular 
movement  in  one  direction  renders  that  movement  easier  after- 


THE  ORIGIN   OP  THE  FORMS  OF   LIFE.  41 

ward,  and  in  proportion  to  the  frequency  of  repetition  ;  which 
is  equivalent  to  saying  that  functional  activity  facilitates  func- 
tional activity.  Once  accepting  this  as  of  universal  application 
in  biology,  we  have  an  explanation  of  the  origin,  the  compara- 
tive rigidity,  and  the  necessity  of  habit.  There  must  be  a  phys- 
ical basis  or  correlative  of  all  mental  and  moral  habits,  as  well 
as  those  that  may  be  manifested  during  sleep,  and  so  purely  in- 
dependent of  the  will  and  consciousness.  We  are  brought,  in 
fact,  to  the  habits  of  cells  in  considering  those  organs,  and  that 
combination  of  structures  which  makes  up  the  complex  individ- 
ual mammal.  It  is  further  apparent  that  if  the  cell  can  trans- 
mit its  nature  as  altered  by  its  experiences  at  all,  then  habits 
must  be  hereditary,  which  is  known  to  be  the  case. 

Instincts  seem  to  be  but  crystallized  habits,  the  inherited 
results  of  ages  of  functional  activity  in  certain  well-defined 
directions. 

To  a  being  with  a  highly  developed  moral  nature  like  man, 
the  law  of  habit  is  one  of  great,  even  fearful  significance.  We 
make  to-day  our  to-morrow,  and  in  the  present  we  are  deciding 
the  future  of  others,  as  our  present  has  been  made  for  us  in  part 
by  our  ancestors.  We  shall  not  pursue  the  subject,  which  is  of 
boundless  extent,  further  now,  but  these  somewhat  general 
statements  will  be  amplified  and  applied  in  future  chapters. 


THE  ORIGIN  OF  THE  FORMS  OF  LIFE. 

It  is  a  matter  of  common  observation  that  animals  originate 
from  like  kinds,  and  plants  from  forms  resembling  themselves ; 
while  most  carefully  conducted  experiments  have  failed  to  show 
that  living  matter  can  under  any  circumstances  known  to  us 
arise  from  other  than  living  matter. 

That  in  a  former  condition  of  the  universe  such  may  have 
been  the  case  has  not  been  disproved,  and  seems  to  be  the  logical 
outcome  of  the  doctrine  of  evolution  as  applied  to  the  universe 
generally. 

By  evolution  is  meant  the  derivation  of  more  complex  and 
differentiated  forms  of  matter  from  sirajjler  and  more  homogene- 
ous ones.  When  this  theory  is  applied  to  organized  or  living 
forms,  it  is  termed  organic  evolution.  There  are  two  views  of 
the  origin  of  life:  tlie  one,  tliat  each  distinct  group  of  plants 
and  animals  was  independently  created ;  while  by  "  creation  "  is 
simply  meant  tliat  they  came  into  being  in  a  manner  we  know 


42  ANIMAL  PHYSIOLOGY. 

not  how,  in  obedience  to  the  will  of  a  First  Cause.  The  other 
view  is  denominated  the  theory  of  descent  with  modification^ 
the  theory  of  transmutation,  organic  evolution  etc.,  which 
teaches  that  all  the  various  forms  of  life  have  been  derived 
from  one  or  a  few  primordial  forms  in  harmony  with  the  recog- 
nized principles  of  heredity  and  variability.  The  most  widely 
known  and  most  favorably  received  exposition  of  this  theory  is 
that  of  Charles  Darwin,  so  that  his  views  will  be  first  presented 
in  the  form  of  a  hypothetical  case.  Assume  that  one  of  a  group 
of  living  forms  varies  from  its  fellows  in  some  particular,  and 
mating  with  another  that  has  similarly  varied,  leaves  progeny 
inheriting  this  characteristic  of  the  parents,  that  tends  to  be 
still  further  increased  and  rendered  permanent  by  successive 
pairing  with  forms  possessing  this  variation  in  form,  color,  or 
whatever  it  may  be.  We  may  suppose  that  the  variations  may 
be  numerous,  but  are  always  small  at  the  beginning.  Since  all 
animals  and  plants  tend  to  multiply  faster  than  the  means  of 
support,  a  competition  for  the  means  of  subsistence  arises,  in 
which  struggle  the  fittest,  as  judged  by  the  circumstances, 
always  is  the  most  successful ;  and  if  one  must  perish  outright, 
it  is  the  less  fit.  If  any  variation  arises  that  is  unfavorable  in 
this  contest,  it  will  render  the  possessor  a  weaker  competitor : 
hence  it  follows  that  only  useful  variations  are  preserved.  The 
struggle  for  existence  is,  however,  not  alone  for  food,  but  for 
anything  which  may  be  an  advantage  to  its  possessor.  One 
form  of  the  contest  is  that  which  results  from  the  rivalry  of 
members  of  the  same  sex  for  the  possession  of  the  females ;  and 
as  the  female  chooses  the  strongest,  most  beautiful,  most  active, 
or  the  supreme  in  some  respect,  it  follows  that  the  best  leave 
the  greatest  number  of  progeny.  This  has  been  termed  sexual 
selection. 

In  determining  what  forms  shall  survive,  the  presence  of 
other  plants  or  animals  is  quite  as  important  as  the  abun- 
dance of  food  and  the  physical  conditions,  often  more  so.  To 
illustrate  this  by  an  example :  Certain  kinds  of  clover  are  fer- 
tilized by  the  visits  of  the  bumble-bee  alone ;  the  numbers  of 
bees  existing  at  any  one  place  depends  on  the  abundance  of  the 
field-mice  which  destroy  the  nests  of  these  insects ;  the  numbers 
of  mice  will  depend  on  the  abundance  of  creatures  that  prey  on 
the  mice,  as  hawks  and  owls ;  these,  again,  on  the  creatures  that 
specially  destroy  them,  as  foxes,  etc. ;  and  so  on,  the  chain  of 
connections  becoming  more  and  more  lengthy. 

If  a  certain  proportion  of  forms  varying  similarly  were  sep- 


THE  ORIGIN  OF  THE  FORMS  OF  LIFE.  43 

arated  by  auy  great  natural  barrier,  as  a  chain  of  lofty  mount- 
ains or  an  intervening  body  of  water  of  considerable  extent, 
and  so  prevented  from  breeding  with  forms  that  did  not  vary, 
it  is  clear  that  there  would  be  greater  likelihood  of  their  differ- 
ences being  preserved  and  augmented  up  to  the  point  of  their 
greatest  usefulness. 

We  may  now  inquire  whether  such  has  actually  been  the 
course  of  events  in  nature.  The  evidence  may  be  arranged 
under  the  follo^ving  heads  : 

1.  Morphology. — Briefly,  there  is  much  that  is  common  to 
entire  large  groups  of  animals ;  so  great,  indeed,  are  the  resem- 
blances throughout  the  whole  animal  kingdom,  that  herein  is 
found  the  strongest  argument  of  all  for  the  doctrine  of  descent. 
To  illustrate  by  a  single  instance — fishes,  reptiles,  birds,  and 
mammals  possess  in  common  a  vertebral  column  bearing  the 
same  relationship  to  other  parts  of  the  animal.  It  is  because  of 
resemblances  of  this  kind,  as  well  as  by  their  differences,  that 
naturalists  are  enabled  to  classify  animals. 

2.  Embryology. — In  the  stages  through  which  animals  pass 
in  their  development  from  the  ovum  to  the  adult,  it  is  to  be  ob- 
served that  the  closer  the  resemblance  of  the  mature  organism 
in  different  groups,  the  more  the  embryos  resemble  one  another. 
Up  to  a  certain  stage  of  development  the  similarity  between 
groups  of  animals,  widely  separated  in  their  post-embryonic 
life,  is  marked :  thus  the  embryo  of  a  reptile,  a  bird,  and  a  mam- 
mal have  much  in  common  in  their  earlier  stages.  The  embryo 
of  the  mammal  passes  through  stages  which  represent  condi- 
tions which  are  permanent  in  lower  groups  of  animals,  as  for 
example  that  of  the  branchial  arches,  which  are  represented  by 
the  gills  in  fishes.  It  may  be  said  that  the  developmental  his- 
tory of  the  individual  (ontogeny)  is  a  brief  recapitulation  of 
the  development  of  the  species  (phylogeny).  Apart  from  the 
theory  of  descent,  it  does  not  seem  possible  to  gather  the  true 
significance  of  such  facts,  which  will  become  plainer  after  the 
study  of  the  chapters  on  reproduction. 

3.  Mimicry  may  be  cited  as  an  instance  of  useful  adapta- 
tion. Thus,  certain  beetles  resemble  bees  and  wasps,  whicli  lat- 
ter are  protected  by  stings.  It  is  believed  that  such  groups  of 
beetles  as  these  arose  by  a  species  of  selection  ;  those  escajjing 
enemies  which  clianced  to  resemble  dreaded  insects  most,  so 
that  birds  wliich  were  accustomed  to  prey  on  beetles,  yet  feared 
bees,  would  likewise  avoid  the  mimicking  forms. 

4.  Rudimentary  Organs. — Organs  whicli  were  once  functional 


44 


ANIMAL  PHYSIOLOGY. 


Fig.  47. — Shows  the  embryos  of  four  mammals  in  the  three  corresponding  stages :  of  a  hog  (H), 
calf  (C),  rabbit  (R),  and  a  man  (M).  The  conditions  of  the  three  different  stages  of  devel- 
opment, which  the  three  cross-rows  (I,  II,  III)  represent,  are  selected  to  correspond  as 
exactly  as  possible.  The  first,  or  upper  cross-row,  I,  represents  a  very  early  stage,  with 
gill-openings,  and  without  limbs.  The  second  (middle)  cross-row,  II,  shows  a  somewhat 
later  stage,  with  the  first  rudiments  of  limbs,  while  the  gill-openings  are  yet  retained. 
The  third  (lowest)  cross-row.  III,  shows  a  still  later  stage,  with  the  limbs  more  developed 
and  the  gill-openings  lost.  The  membranes  atid  appendages  of  the  embryonic  body  (the 
amnion,  yelk-sac,  allantois)  are  omitted.  The  whole  twelve  figures  are  slightly  magnified, 
the  upper  ones  more  than  the  lower.  To  facilitate  the  comparison,  they  are  all  reduced 
to  nearly  the  same  size  in  the  cuts.  All  the  embryos  are  seen  from  the  left  side  :  the  head 
extremity  is  above,  the  tail  extremity  below  ;  the  arched  back  turned  to  the  right.  The 
letters  indicate  the  same  parts  in  all  the  twelve  figures,  namely :  v,  fore-brain  ;  z,  twixt- 
brain  ;  m,  mid-brain ;  h,  hind-brain  ;  n,  after-brain  ;  r,  spinal  marrow  :  e,  nose  ;  a,  eye  ; 
o,  ear  ;  fc,  gill-arches  ;  g,  heart ;  w,  vertebral  colmnn ;  /,  fore-limbs  ;  b,  hind-limbs  ;  s,  tail. 
(After  Haeekel.) 


THE  ORIGIN   OF  THE   FORMS   OF   LIFE.  45 

in  a  more  ancient  form^  but  serve  no  use  in  tlie  creatures  in 
which  they  are  now  found,  have  reached,  it  is  thought,  their 
rudimentary  condition  through  long  periods  of  comparative 
disuse,  in  many  generations.  Such  are  the  rudimentary  mus- 
cles of  the  ears  of  man,  or  the  undeveloped  incisor  teeth  found 
in  the  upper  jaw  of  ruminants. 

5.  Geographical  Distribution. — It  can  not  be  said  that  animals 
and  plants  are  always  found  in  the  localities  where  they  are 
best  fitted  to  flourish.  This  has  been  well  illustrated  within 
the  lifetime  of  the  present  generation,  for  the  animals  intro- 
duced into  Australia  have  many  of  them  so  multiplied  as  to 
displace  the  forms  native  to  that  country.  But,  if  we  assume 
that  migrations  of  animals  and  transmutations  of  species  have 
taken  place,  this  difficulty  is  in  great  part  removed. 

0.  Paleontology. — The  rocks  bear  record  to  the  former  exist- 
ence of  a  succession  of  related  forms ;  and,  though  all  the  in- 
termediate links  that  probably  existed  have  not  been  found, 
the  apparent  discrepancy  can  be  explained  by  the  nature  of 
the  circumstances  under  which  fossil  forms  are  preserved ;  and 
the  "  imperfection  of  the  geological  record." 

It  is  only  in  the  sedimentary  rocks  arising  from  mud  that 
fossils  can  be  preserved,  and  those  animals  alone  with  hard 
parts  are  likely  to  leave  a  trace  behind  them ;  while  if  these 
sedimentary  rocks  with  their  inclosed  fossils  should,  owing  to 
enormoiis  pressure  or  heat  be  greatly  changed  (metamorphosed), 
all  trace  of  fossils  must  disappear — so  that  the  earliest  forms 
of  life,  those  that  would  most  naturally,  if  preserved  at  all,  be 
found  in  the  most  ancient  rocks,  are  wanting,  in  consequence 
of  the  metamorphism  which  such  formations  have  undergone. 
Moreover,  our  knowledge  of  the  animal  remains  in  the  earth's 
crust  is  as  yet  very  incomplete,  though,  the  more  it  is  explored, 
tlie  more  the  evidence  gathers  force  in  favor  of  organic  evolu- 
tion. But  it  must  be  remembered  that  those  groups  constitut- 
ing species  ai-c  in  geological  time  intermediate  links. 

7.  Fossil  and  Existing  Species. — If  the  animals  and  plants  now 
peopling  the  earth  were  entirely  different  from  those  that  flour- 
ished in  the  past,  the  objections  to  the  doctrine  of  descent  would 
be  greatly  strengthened ;  but  when  it  is  found  that  there  is  in 
some  cases  a  scarcely  broken  succession  of  forms,  great  force  is 
added  to  the  arguments  by  which  we  are  led  to  infer  the  con- 
nection of  all  forms  with  one  another. 

To  illustrate  by  a  single  instance:  the  existing  group  of 
horses,  with  a  single  toe  to  each  foot,  was  preceded  in  geological 


46 


ANIMAL  PHYSIOLOGY. 


time  in  America  by  forms  with  a  greater  number  of  toes,  the 
latter  increasing  according  to  the   antiquity   of    the    group. 


Fig.  48.— Bones  of  the  feet  of  the  different  genera  of  Equidce  (after  Marsh),  a,  foot  of  Oro- 
hippus  (Eocene) ;  b,  foot  of  Anchitherium  (Lower  Miocene) ;  c,  foot  of  Hipparion  (Plio- 
cene) ;  d,  foot  of  the  recent  genus  Equus. 

These  forms  occur  in  succeeding  geological  formations.  It  is 
impossible  to  resist  the  conclusion  that  they  are  related  gene- 
alogically (phylogenetically). 

8.  Progression. — Inasmuch  as  any  form  of  specialization  that 
would  give  an  animal  or  plant  an  advantage  in  the  struggle  for 
existence  would  be  preserved,  and  as  in  most  cases  when  the 
competing  forms  are  numerous  such  would  be  the  case,  it  is 
possible  to  understand  how  the  organisms  that  have  appeared 
have  tended,  on  the  whole,  toward  a  most  pronounced  pro- 
gression in  the  scale  of  existence.  This  is  well  illustrated 
in  the  history  of  civilization.  Barbarous  tribes  give  way  be- 
fore civilized  man  with  the  numberless  subdivisions  of  labor 
he  institutes  in  the  social  organism.  It  enables  greater  num- 
bers to  flourish  as  the  competition  is  not  so  keen  as  if  activities 
could  be  exercised  in  a  few  directions  only. 

9.  Domesticated  Animals. — Darwin  studied  our  domestic  ani- 
mals long  and  carefully,  and  drew  many  important  conclusions 
from  his  researches.  He  was  convinced  that  they  had  all  been 
derived  from  a  few  wild  representatives,  in  accordance  with  the 
principles  of  natural  selection.  Breeders  have,  both  consciously 
and  unconsciously,  formed  races  of  animals  from  stocks  which 
the  new  groups  have  now  supplanted  ;  while  primitive  man  had 
tamed  various  species  which  he  kept  for  food  and  to  assist  in 
the  chase,  or  as  beasts  of  burden.  It  is  impossible  to  believe 
that  all  the  different  races  of  dogs  have  originated  from  dis- 
tinct wild  stocks,  for  many  of  them  have  been  formed  within 
recent  periods ;  in  fact,  it  is  likely  that  to  the  jackal,  wolf,  and 


THE  ORIGIN  OF  THE   FORMS   OF    LIFE. 


47 


fox,  must  we  look  for  the  wild  progenitors  of  our  dogs.  Dar- 
win concluded  that,  as  man  had  only  utilized  the  materials  Na- 
ture provided  in  forming  his  races  of  domestic  animals,  he  had 
availed  himself  of  the  variations  that  arose  spontaneously,  and 
increased  and  fixed  them  by  breeding  those  possessing  the  same 
variation  together,  so  the  like  had  occurred  without  his  aid  in 
nature  among  wild  forms. 

Evolutionists  are  divided  as  to  the  origin  of  man  himself ; 
some,  like  Wallace,  who  are  in  accord  with  Darwin  as  to  the 


^   3 


Fio.  49.— Skeleton  of  hand  or  fore-foot  of  six  mammals.  I,  man  ;  II,  dog  ;  III,  pig  :  FV,  ox  ; 
V,  tapir  :  VI.  horse,  r,  radius;  it,  ulna  ;  a,  scaphoid  ;  b.  semi-lunar  ;  c,  triquetrum  (cunei- 
form) ;  d.  trapezium  ;  e.  trapezoid  ;  /,  capitatum  (unciform  process)  ;  g,  hamatum  (unci- 
form bone) ;  p.  pisiform  :  1,  thumb  ;  2.  digit ;  3.  middle  finger  ;  4.  ring-finger  ;  5,  little 
finger.    (After  Gegenbaur.) 

origin  of  living  forms  in  general,  believe  that  the  theory  of 
natural  selection  does  not  suffice  to  account  for  the  intellectual 
and  moral  nature  of  man.  Wallace  believes  that  man's  body 
has  been  derived  from  lower  forms,  but  that  his  higher  nature 
is  the  result  of  some  unknown  law  of  accelerated  development ; 
while  Darwin,  and  those  of  his  way  of  thinking,  consider  that 
man  in  his  entire  nature  is  but  a  grand  development  of  powers 
existing  in  minor  degree  in  the  animals  behnv  him  in  the  scale. 
Sumlnary. — Every  group  of  animals  and  plants  tends  to  in- 
crease in  numbers  in  a  geometrical  progression,  and  must,  if 
unchecked,  overrun  the  earth.  Every  variety  of  animals  and 
Y>lants  imparts  to  its  offspring  a  general  resemblance  to  itself, 
but  with  minute  variations  from  the  original.  The  variations 
of  oflfspring  may  be   in   any  direction,  and   by   accumulation 


ANIMAL  PHYSIOLOGY. 


THE   ORIGIN   OF   THE   FORMS   OF   LIFE. 


49 


X 


■^ 


Fio.  55.— a,  chimpanzee  ;  6,  iiforilla  ;  c,  orang  ;  d,  negro.    (Haeckel.) 


50 


ANIMAL   PHYSIOLOGY. 


Fig.  56.— Head  of  a  nose-ape  iSeni- 
nopithecus  nasicux)  from  Bor- 
neo.   (After  Brehm.) 


Fig.  57.— Head  of  Julia  Pas- 
trana. (From  a  photo- 
graph by  Hintze.) 


constitute  fixed  differences  by  which  a  new  group  is  marked 
off.  In  the  determination  of  the  variations  that  persist,  the  law 
of  survival  of  the  fittest  operates. 


EEPRODUCTION. 

As  has  been  already  noticed,  protoplasm,  in  whatever  form, 
after  passing  through  certain  stages  in  development,  undergoes 
a  decline,  and  finally  dies  and  joins  the  world  of  unorganized 
matter ;  so  that  the  permanence  of  living  things  demands  the 
constant  formation  of  new  individuals.  Groups  of  animals 
and  plants  from  time  to  time  become  extinct;  but  the  lifetime 
of  the  species  is  always  long  compared  with  that  of  the  individ- 
ual. Reproduction  by  division  seems  to  arise  from  an  exigency 
of  a  nutritive  kind,  best  exemplified  in  the  simpler  organisms. 
When  the  total  mass  becomes  too  great  to  be  supported  by 
absorption  of  pabulum  from  without  by  the  surface  of  the 
body,  division  of  the  organism  must  take  place,  or  death  ensues. 
It  appears  to  be  a  matter  of  indifference  how  this  is  accom- 
plished, whether  by  fission,  endogenous  division,  or  gemmation, 
so  long  as  separate  portions  of  protoplasm  result,  capable  of 
leading  an  independent  existence.  The  very  undifferentiated 
character  of  these  simple  forms  prepares  us  to  understand  how 
each  fragment  may  go  through  the  same  cycle  of  changes  as 
the  parent  form.  In  such  cases,  speaking  generally,  a  million 
individuals  tell  the  same  biological  story  as  one ;  yet  these 
must  exist  as  individuals,  if  at  all,  and  not  in  one  great  united 
mass.  But  in  the  case  of  conjugation,  which  takes  place  some- 
times in  the  same  groups  as  also  multiply  by  division  in  its 
various  forms,  there  is  plainly  an  entirely  new  aspect  of  the 


REPRODUCTION".  51 

case  presented.  We  have  already  shown  that  no  two  cells,  how- 
ever much  alike  they  may  seem  as  regards  form  and  the  cir- 
cumstances under  which  they  exist,  can  have,  in  the  nature  of 
the  case,  precisely  the  same  history,  or  be  the  subjects  of  ex- 
actly the  same  experiences.  We  have  also  pointed  out  that  all 
these  phenomena  of  cell-life  are  known  to  us  only  as  adaptations 
of  internal  to  external  conditions ;  for,  though  we  may  not  be 
always  able  to  trace  this  connection,  the  inference  is  justi- 
fiable, because  there  are  no  facts  known  to  us  that  contradict 
such  an  assumption,  while  those  that  are  within  our  knowledge 
bear  out  the  generalization.  We  have  already  learned  that  liv- 
ing things  are  in  a  state  of  constant  change,  as  indeed  are  all 
things ;  we  have  observed  a  constant  relation  between  certain 
changes  in  the  environment,  or  sum  total  of  the  surrounding 
conditions,  as,  for  example,  temperature  and  the  behavior  of 
the  protoplasm  of  plants  and  animals ;  so  that  we  must  believe 
that  any  one  form  of  protoplasm,  however  like  another  it  may 
seem  to  our  comparatively  imperfect  observation,  is  different 
in  some  respects  from  every  other — as  different,  relatively,  as 
two  human  beings  living  in  the  same  community  during  the 
whole  of  their  lives ;  and  in  many  cases  as  unlike  as  individuals 
of  very  different  nationality  and  history.  We  are  aware  that 
when  two  such  persons  meet,  provided  the  unlikeness  is  not  so 
great  as  to  prevent  social  intercourse,  intercommunication  may 
prove  very  instructive.  Indeed,  the  latter  grows  out  of  the 
former ;  our  illustration  is  itself  explained  by  the  law  we  are 
endeavoring  to  make  plain.  It  would  appear,  then,  that  con- 
tinuous division  of  protoplasm  without  external  aid  is  not  pos- 
sible ;  but  that  the  vigor  necessary  for  this  must  in  some  way 
be  imparted  by  a  particle  (cell)  of  similar,  yet  not  wholly  like, 
protoplasm.  This  seems  to  furnish  an  explanation  of  the  neces- 
sity for  the  conjugation  of  living  forms,  and  the  differentiation 
of  sex.  Very  frequently  conjugation  in  the  lowest  animals  and 
plants  is  followed  by  long  periods  when  division  is  the  prevail- 
ing method  of  reproduction.  It  is  worthy  of  note,  too,  that 
when  living  forms  conjugate,  they  both  become  quiescent  for  a 
longer  or  shorter  time.  It  is  as  though  a  period  of  preparation 
preceded  one  of  extraordinary  activity.  We  can  at  present 
trace  only  a  few  of  the  ste{>s  in  this  rejuvenation  of  life-stuff. 
Some  of  these  have  been  already  indicated,  which,  with  others, 
will  now  be  further  studied  in  this  division  of  our  subject,  both 
because  reproduction  throws  so  much  light  on  cell-life,  and  be- 
'•ause  it  is  so  important  for  the  understanding  of  the  physio- 


52 


ANIMAL  PHYSIOLOGY. 


logical  behavior  of  tissues  and  organs.  It  may  be  said  to  be 
quite  as  important  that  the  ancestral  history  of  the  cells  of  an 
organism  be  known  as  the  history  of  the  units  composing  a 
community.  A,  B,  and  C  can  be  much  better  understood  if 
we  know  something  alike  of  the  history  of  their  race,  their  an- 
cestors, and  their  own  past ;  so  is  it  with  the  study  of  any  indi- 
vidual, animal,  or  group  of  animals  or  plants.  Accordingly, 
embryology,  or  the  history  of  the  origin  and  development  of 
tissues  and  organs,  will  occupy  a  prominent  place  in  the  va- 
rious chapters  of  this  work.  The  student  will,  therefore,  at 
the  outset  be  furnished  with  a  general  account  of  the  subject, 
while  many  details  and  applications  of  principles  will  be  left 
for  the  chapters  that  treat  of  the  functions  of  the  various  organs 
of  animals.  The  more  knowledge  the  student  possesses  of  zo- 
ology the  better,  while  this  science  will  appear  in  a  new  light 
under  the  study  of  embryology. 

Animals  are  divisible,  according  to  general  structure,  into 
Protozoa,  or  unicellular  animals,  and  Metazoa,  or  multicellular 
forms — that  is,  animals  composed  of  cell  aggregates,  tissues,  or 
organs.  Among  the  latter  one  form  of  reproduction  appears 
for  the  first  time  in  the  animal  kingdom,  and  becomes  all  but 
universal,  though  it  is  not  the  exclusive  method ;  for,  as  seen  in 
Hydra,  both  this  form  of  generation  and  the  more  primitive 
gemmation  occur.  It  is  known  as  sexual  multiplication,  which 
usually,  though  not  invariably,  involves  conjugation  of  two  un- 
like cells  which  may  arise  in  the  same  or  different  individuals. 
That  these  cells,  known  as  the  male  and  female  elements,  the 
ovum  and  the  spermatozoon,  are  not  necessarily  radically  differ- 
ent, is  clear  from  the  fact  that  they  may  arise  in  the  one  individ- 
ual from  the  same  tissue  and  be  mingled  together.  These  cells, 
however,  like  all  others,  tell  a  story  of  continual  progressive 
differentiation  corresponding  to  the  advancing  evolution  of 
higher  from  lower  forms.  Thus  liermaphroditisrii,  or  the  coex- 
istence of  organs  for  the  production  of  male  and  of  female  cells 
in  the  same  individual,  is  confined  to  invertebrates,  among 
which  it  is  rather  the  exception  than  the  rule.  Moreover,  in 
such  hermaphrodite  forms  the  union  of  cells  with  greater  differ- 
ence in  experiences  is  provided  for  by  the  union  of  different  in- 
dividuals, so  that  commonly  the  male  cell  of  one  individual 
unites  with  (fertilizes)  the  female  cell  of  a  different  individual. 
It  sometimes  happens  that  among  the  invertebrates  the  cells 
produced  in  the  female  organs  of  generation  possess  the  power 
of  division,  and  continued  development  wholly  independently  of 


REPRODUCTION.  53 

the  access  of  any  male  cell  {parthenogenesis) ;  such,  however,  is 
almost  never  the  exclusive  method  of  increase  for  any  group  of 
animals,  and  is  to  be  regarded  as  a  retention  of  a  more  ancient 
method,  or  perhaps  rather  a  reversion  to  a  past  biological  con- 
dition. No  instance  of  complete  parthenogenesis  is  known 
among  vertebrates,  although  in  birds  partial  development  of  the 
egg  may  take  place  independently  of  the  influence  of  the  male 
sex.  The  best  examples  of  parthenogenesis  are  to  be  found 
among  insects  and  crustaceans. 

It  is  to  be  remembered  that,  while  the  cells  which  form  the 
tissues  of  the  body  of  an  animal  have  become  specialized  to 
discharge  one  particular  function,  they  have  not  wholly  lost 
all  others ;  they  do  not  remain  characteristic  amoeboids,  as  we 
may  term  cells  closely  resembling  Amoeba  in  behavior,  nor  do 
they  wholly  forsake  their  ancestral  habits.  They  all  retain  the 
power  of  reproduction  by  division,  especially  when  young  and 
most  vigorous ;  for  tissues  grow  chiefly  by  the  production  of 
new  cells  rather  than  the  enlargement  of  already  mature  ones. 
Cells  wear  out  and  must  be  replaced,  which  is  effected  by  the 
processes  already  described  for  Amoeba  and  similar  forms. 
Moreover,  there  is  retained  in  the  blood  of  animals  an  army  of 
cells,  true  amoeboids,  ever  ready  to  hasten  to  repair  tissues  lost 
by  injury.  These  are  true  remnants  of  an  embryonic  condition ; 
for  at  one  period  all  the  cells  of  the  organism  were  of  this 
undifferentiated,  plastic  character.  But  the  cell  (ovum)  from 
which  the  individual  in  its  entirety  and  with  all  its  complexity 
arises  mostly  by  the  union  with  another  cell  {spermatozoon), 
must  be  considered  as  one  that  has  remained  unspecialized 
and  retained,  and  perhaps  increased  its  reproductive  functions. 
They  certainly  have  become  more  complex.  The  germ-cell 
may  be  considered  unspecialized  as  regards  other  functions,  but 
highly  .specialized  in  the  one  direction  of  exceedingly  great 
capacity  for  growth  and  complex  division,  if  we  take  into  ac- 
count the  whole  chain  of  results ;  though  in  considering  this  it 
must  be  borne  in  mind  that  after  a  certain  stage  of  division 
each  individual  cell  repeats  its  ancestral  history  again ;  that  is 
to  .say,  it  divides  and  gives  rise  to  cells  which  progress  in  turn 
as  well  as  multiply.  From  another  point  of  view  the  ovum  is 
a  marvelous  storehouse  of  energy,  latent  or  potential,  of  course, 
but  under  proper  conditions  liberated  in  varied  and  unexpe(;ted 
forms  of  force.  It  is  a  sort  of  storeliouse  of  biological  energy 
in  the  most  concentrated  form,  the  liberation  of  which  in  sim- 
pler forms  gives  rise  to  that  complicated  chain  of  events  which 


54: 


ANIMAL   PHYSIOLOGY. 


is  termed  by  the  biologist  development,  but  wMch.  may  be  ex- 
pressed by  the  physiologist  as  the  transformation  of  potential 
into  kinetic  energy,  or  the  energy  of  motion.  Viewed  chemic- 
ally, it  is  the  oft-repeated  story  of  the  production  of  forms,  of 
greater  stability  and  simplicity,  from  more  unstable  and  com- 
plex ones,  involving  throughout  the  process  of  oxidation ;  for  it 
must  ever  be  kept  in  mind  that  life  and  oxidation  are  concomi- 
tant and  inseparable.  The  further  study  of  reproduction  in  the 
concrete  will  render  the  meaning  and  force  of  many  of  the 
above  statements  clearer. 


The  Ovum. 

The  typical  female  cell,  or  ovum,  consists  of  a  mass  of  proto- 
plasm, usually  globular  in  form,  containing  a  nucleus  and  nu- 
cleolus. 

The  ovum  may  or  may  not  be  invested  by  a  membrane ;  the 
protoplasm  of  the  body  of  the  cell  is  usually  highly  granular, 
and  may  have  stored  up  within  it  a  varying  amount  of  proteid 
material  (food-yelk),  which  has  led  to  division  of  ova  into 
classes,  according  to  the  manner  of  distribution  of  this  nutri- 
tive reserve.  It  is  either  concentrated  at  one  pole  {telolecith- 
al) ;  toward  the  center  [centrolecitlial)  ;  or  evenly  distributed 

throughout  {alecithal).  Dur- 
ing development  this  material 
is  converted  by  the  agency  of 
the  cells  of  the  young  organ- 
ism {embryo)  into  active  pro- 
toplasm ;  in  a  word,  they  feed 
upon  and  assimilate  or  build 
up  this  food-stuff  into  their 
own  substance,  as  Amoeba  does 
with  any  proteid  material  it 
appropriates. 

The  nucleus  {germinal  vesi- 
cle) is  large  and  well-defined, 
and  contains  within  itself  a 
highly  refractive  nucleolus 
{germinal  spot).  These  closely 
resemble  in  general  the  rest  of 
the  cell,  but  stain  more  deeply  and  are  chemically  different  in 
that  they  contain  nucleine  {nucleoplasm,  cliromatin). 

It  will  be  observed  that  the  ovum  differs  in  no  essential  par- 


FiG.  58. — Semi-diagrammatic  representation 
of  a  mammalian  ovum  (Schafer).  Highly- 
magnified,  zp,  zona  pellucida  ;  vi,  vitel- 
lus  ;  gv,  germinal  vesicle  ;  gs,  germinal 
spot. 


REPRODUCTION. 


55 


Fig.  59. — A  human  egg  (much  enlarged)  from  the  ovary  of  a  female.  The  whole  egg  is  a 
simple  spherical  cell.  The  greater  part  of  this  cell  is  formed  bj-  the  egg-yelk,  by  the  gran- 
ular cell-substance  (protoplasm),  consisting  of  innumerable  yelk-granules  with  a  little 
inter-granular  substance.  In  the  upper  part  of  the  yelk  lies  the  bright,  globular,  germ- 
vesicle,  corresponding  with  the  cell-kernel  (dwc/eu.s).  This  contains  a  darker  germ-spot, 
answering  to  the  nucleolus.  The  globular  yelk-mass  is  surrounded  by  a  thick,  light- 
colored  egg-membrane  (zona  pellucida.  or  chorion).  This  is  traversed  by  very  numerous 
hair-like  lines,  radiating  toward  the  central  point  of  the  ma.ss  :  these  are  the  porous 
canals,  through  which,  in  the  course  of  fertilization,  the  thread-shaped,  active  sperm-cells 
penetrate  into  the  egg-yelk.    (Haeckel.) 


ticular  of  structure  from  other  cells.  Its  differences  are  hidden 
ones  of  molecular  structure  and  functional  behavior.  In  ac- 
cordance with  the  diverse  circumstances  under  which  ova 
mature  and  develop,  certain  variations  in  structure,  mostly  of 
the  nature  of  additions,  present  themselves. 

Thus,  ova  may  be  naked,  or  provided  with  one  or  more 
coverings.  In  vertebrates  there  are  usually  two  membranes 
around  the  protoplasm  of  the  ovum :  a  delicate  covering  ( Vi- 
telline membrane),  beneath  which  there  is  another,  which 
is  sieve-like  from  numerous  perforations  {zona  radiata,  or  z. 
pellucida).  The  egg  membrane  may  be  impregnated  with  lime 
salts  (shell).  Between  the  membranes  and  the  yelk  there  is  a 
fluid  albuminous  substance  secreted  by  the  glands  of  the  ovi- 
duct, or  by  other  special  glands,  which  jjrovide  proteid  nutri- 
ment in  different  x>hysical  condition  from  that  of  the  yolk. 

The  general  naked-eye  apjjearances  of  the  ovum  may  be 
learned  from  the  examination  of  a  hen's  egg,  which  is  one  of 


56 


ANIMAL  PHYSIOLOGY. 


the  most  complicated  known,  inasmuch  as  it  is  adapted  for 
development  outside  of  the  body  of  the  mother,  and  must,  con- 
sequently, be  capable  of  preserving  its  form  and  essential  vital 
properties  in  a  medium  in  which  it  is  liable  to  undergo  loss  of 
water,  protected  as  it  now  is  with  shell,  etc.,  but  which,  at  the 


ch.l 


Fig.  60.— Diagrammatic  section  of  an  unimpreffnated  fowl's  egg  (Foster  and  Balfour,  after 
Allen  Thomson).  6i,  blastoderm  or  cicatricula  ;  w.  y,  white  yolk  ;  y.  y,  yellow  yelk  ;  ch.  I, 
chalaza  ;  i.  s.  ni,  inner  layer  of  shell  membrane  ;  s.  in,  outer  layer  of  shell  membrane  ;  s, 
shell ;  a.  c.  h,  air-space  ;  w,  the  white  of  the  egg  ;  v.  t,  vitelline  membrane  ;  x,  the  denser 
albuminous  layer  lying  next  the  vitelline  membrane. 

same  time,  permits  the  entrance  of  oxygen  and  moisture,  and 
conducts  heat,  all  being  essential  for  the  development  of  the 
germ  within  this  large  food-mass.  The  shejl  serves,  evidently, 
chiefly  for  protection,  since  the  eggs  of  serpents  (snakes,  turtles, 
etc.)  are  provided  only  with  a  very  tough  membranous  cover- 
ing, this  answering  every  purpose  in  eggs  buried  in  sand  or 
otherwise  protected  as  theirs  usually  are.  As  the  hen's  egg  is 
that  most  readily  studied  and  most  familiar,  it  may  be  well  to 
describe  it  in  somewhat  further  detail,  as  illustrated  in  the 
above  figure,  from  the  examination  of  which  it  will  be  ap- 
parent that  the  yelk  itself  is  made  up  of  a  white  and  yellow 
portion  distributed  in  alternating  zones,  and  composed  of  cells 
of  different  microscopical  appearances.  The  clear  albumen  is 
structureless. 

The  relative  distribution,  and  the  nature  of  the  accessory  or 
non-essential  parts  of  the  hen's  egg,  will  be  understood  when  it 
is  remembered  that,  after  leaving  its  seat  of  origin,  which  will 
be  presently  described,  the  ovum  passes  along  a  tube  (oviduct) 


REPRODUCTION. 


57 


Idv  a  movement  imparted  to  it  by  the  muscular  walls  of  the 
latter,  similar  to  that  of  the  gullet  during  the  swallowing  of 
food ;  that  this  tube  is  provided  with  glands  which  secrete  in 
turn  the  albumen,  the  membrane  (outer),  the  lime  salts  of  the 
shell,  etc.  The  twisted  appearance  of  the  rope-like  structures 
(chalazce)  at  each  end  is  owing  to  the  spiral  rotatory  movement 
the  egg  has  undergone  in  its  descent. 

The  air-chamber  at  the  larger  end  is  not  present  from  the 
first,  but  results  from  evaporation  of  the  fluids  of  the  albumen 
and  the  entrance  of  atmos]oheric  air  after  the  egg  is  laid  some 
time. 

The  Origin  and  Development  of  the  Ovum. 

Between  that  protrusion  of  cells  which  gives  rise  to  the 
bud  which  develops  directly  into  the  new  individual,  and  that 
which  forms  the  ovary  with- 


rS.       TTE. 


PS. 


in  which  the  ovum  as  a  mod- 
ified cell  arises,  there  is  not 
in  Hydra  much  difference  at 
first  to  be  observed. 

In  the  mammal,  however, 
the  ovary  is  a  more  complex 
etructure,  though,  relatively 
to  many  organs,  still  simple. 
It  consists,  in  the  main,  of 
connective  tissue  supplied 
with  vessels  and  nerves  in- 
closing m(jdifications  of  that 
tissue  (Graafian  follicles) 
within  which  the  ovum  is 
matured.  The  ovum  and  the 
follicles  arise  from  an  inver- 
sion of  epithelial  cells,  on  a 
portion  of  the  body  cavity 
(fjerminal  ridge),  which  give 
rise  to  the  ovum  itself,  and 
the  other  cells  surrounding 
it  in  the  Graafian  follicle. 
At  first  these  inversions  form 
tubules  (egg-tubes)  which  lat- 
er bec(;nie  broken  up  into  iso- 
lated nests  of  cells,  the  ft^re-runners  of  the  Graafian  follicles. 

The  Graafian  follicle  consists  externally  of  a  fibrous  cai)sule 


Ei.    Mp.         • 

Fig.  61.— Section  through  portion  of  the  ovary 
of  mammal,  illustrating  mode  of  develop- 
ment of  the  Graafian  follicles  (Wieder- 
sheim).  D,  discus  proligerus  ;  Ei,  ripe  ovum  ; 
(t,  follicular  cells  of  germinal  epithelium  ; 
(I,  blood-vessels  :  A',  germinal  vesicle  (nucle- 
us) and  germinal  spot  (nucleolus) :  KE.  ger- 
minal epithelium  :  Lf.  Ifquor  folliculi  ;  Afg, 
membrana  or  tunica  granulosa,  or  follicular 
epithelium  ;  Mik  zona  pellucida  :  PS,  in- 
grf)wths  from  tlie  germinal  ei)ithelium,  ova- 
rian tubes,  liy  means  of  which  some  of  the 
nests  retain  tlieir  connection  with  the  epithe- 
lium :  .S,  cavity  which  appears  within  the 
Graafian  folli<;le  ;  .So,  stroma  of  ovary  ;  Tf, 
theca  follicidi  or  capsule  ;  U,  primitive  ova. 
When  an  ovum  with  its  surrounding  cells 
ha«  becf)me  se[)arated  from  the  nest,  it  is 
known  a«  a  Graafian  follicle. 


58 


ANIMAL  PHYSIOLOGY. 


{tunica  fibrosa),  in  close  relation  to  which  is  a  layer  of  capillary 
blood-vessels  {tunica  vasculosa),  the  two  together  forming  the 


Fig.  62.— Sagittal  section  of  the  ovary  of  an  adult  bitch  (after  Waldeyer).  o.  e,  ovarian  epi- 
thelium ;  o.  t,  ovarian  tubes  ;  y.  f,  younger  follicles  ;  o.  /,  older  follicle  ;  d.  p,  discus  pro- 
ligerus,  with  the  ovum  ;  e,  epithelium  of  a  second  ovum  in  the  same  follicle  ;  /.  c,  fibrous 
coat  of  the  follicle  ;  p.  c,  proper  coat  of  the  follicle  ;  e.  /,  epithehum  of  the  follicle  (mem- 
brana  granulosa) :  a.  f.  collapsed  atrophied  follicle  ;  b.  v,  blood-vessels  ;  c.  t,  cell-tubes  of 
the  parovarium,  divided  longitudinally  and  transversely  ;  t.  d,  tubular  depression  of  the 
ovarian  epithelium,  in  the  tissue  of  the  ovary  ;  b.  e,  beginning  of  the  ovarian  epithelium, 
close  to  the  lower  border  of  the  ovary. 

general  covering  {tunica  propria)  for  the  more  delicate  and  im- 
portant cells  within.  Lining  the  tunic  is  a  layer  of  small,  some- 
what cubical  cells  {meinbrana  granulosa) ,  which  at  one  part 
invest  the  ovum  several  layers  deep  {discus  proligerus),  while 
the  remainder  of  the  space  is  filled  by  a  fluid  {liquor  foUiculi) 
probably  either  secreted  by  the  cells  themselves,  or  resulting 
from  the  disintegration  of  some  of  them,  or  both. 


REPRODUCTION. 


59 


In  viewing  a  section  of  the  ovary  taken  from  a  mammal  at 
tlie  breeding-season,  ova  and  Graafian  follicles  may  be  seen  in 
all  stages  of  development — those,  as  a  rule,  nearest  the  surface 
being  the  least  matured.  The  Graafian  follicle  appears  to  pass 
inward,  to  undergo  growth  and  development  and  again  retire 
toward  the  exterior,  where  it  bursts,  freeing  the  ovum,  which  is 
conducted  to  the  site  of  its  future  development  by  appropriate 
mechanism  to  be  described  hereafter. 

Changes  in  the  Ovum  itself. — The  series  of  transformations 
that  take  place  in  the  ovum  before  and  immediately  after  the 
access  of  the  male  element  is,  in  the  opinion  of  many  biolo- 
gists, of  the  highest  significance,  as  indicating  the  course  evolu- 
tion has  followed  in  the  animal  kingdom,  as  well  as  instructive 
in  illustrating  the  behavior  of  nuclei  generally. 

The  germinal  vesicle  may  acquire  powers  of  slow  movement 
(amoeboid),  and  the  germinal  spot  disappear :  the  former  passes 
to  one  surface  (pole)  of  the  ovum  ;  both  these  structures  may 
undergo  that  peculiar  form  of  rearrangement  {karyoTxinesis) 
which  may  occur  in  the  nuclei  and  nucleoli  of  other  cells  prior 
to  division  ;  in  other  words,  the  ovum  has  features  common  to 
it  and  many  other  cells  in  that  early  stage  which  precedes  the 
complicated  transformations  which  constitute  the  future  his- 
tory of  the  ovum. 

A  portion  of  the  changed  nucleus  {aster)  with  some  of  the 
protoplasm  of  the  cell  accumulates  at  one  surface  (pole),  which 


^^^m^ 


Fio.  63.— Formation  of  polar  cells  in  a  star-fish  (Axt<ri«K  i/larialh)  (from  (icikles,  A— K  afUr 
Fol,  L  after  O.  Hertwitfi.  A,  ripe  ovum  wltli  (•(•centric.'  germinal  vesicle  and  spot;  B— D, 
gradual  metamorphosis  of  j^erminal  vesicle  and  spot,  as  seen  in  the  hviiiR  e^Ki  >"to  two 
asters  ;  F.  formation  of  first  pf>lar  cells  and  withdrawal  of  remaininK  part  of  nuclear 
spindle  within  the  ovum  :  (J,  surface  view  of  livinf;  fivum  in  the  first  polar  cell  ;  H,  com- 
pletion of  second  polar  cell  :  I,  a  later  stape,  showinfj  the  remaining;  internal  half  of  the 
spindle  in  the  form  of  two  clear  vesicles  ;  K.  ovum  with  two  polar  cells  and  radial  striae 
round  female  pronucleus,  as  seen  in  the  living  eu'tc  'K.  F.  H,  and  I  from  i)icric  acid  prepa- 
rations) ;  L,  expulsion  of  the  first  polar  cell.     (Iladdon.) 


is  tf*rmed  the  upper  pole  because  it  is  at  this  region  that  the  epi- 
thelial cells  will  be  ultimately  developed,  and  is  separated;  this 
process  is  repeated.     These  bodies  (polar  cells,  polar  (jlohules, 


60 


ANIMAL  PHYSIOLOGY. 


etc.),  then,  are  simply  expelled  ;  they  take  no  part  in  the  devel- 
opment of  the  ovum ;  and  their  extrusion  is  to  be  regarded  as  a 
preparation  for  the  progress  of  the  cell,  whether  this  event  fol- 
lows or  precedes  the  entrance  of  the  male  cell  into  the  ovum. 
It  is  worthy  of  note  that  the  ovum  may  become  amoeboid  in  the 
region  from  which  the  polar  globules  are  expelled. 

The  remainder  of  the  nucleus  {female  pronucleus)  now 
passes  inward  to  undergo  further  changes  of  undoubted  im- 
portance, possibly  those  by  virtue  of  which  all  the  subsequent 
evolution  of  the  ovum  is  determined.  This  brings  us  to  the 
consideration  of  another  cell  destined  to  play  a  brief  but  im- 
portant role  on  the  biological  stage. 

The  Male  Cell  {Spermatozoon). 

This  cell,  almost  without  exception,  consists  of  a  nucleus 
(head)  and  vibratile  cilium.     However,  as  indicating  that  the 


Fig.  64.  -Spermatozoa  (after  Haddon).  Not  drawn  to  scale.  1,  sponge  ;  2,  hydroid  ;  3,  nema- 
tode ;  4.  cray-flsh  ;  5.  snaU  ;  6,  electric  ray  ;  7,  salamander  ;  8,  horse  ;  9,  man.  In  many 
spermatozoa,  as  m  Nos.  7  and  9,  an  extremely  delicate  vibratUe  band  is  present. 


REPRODUCTION. 


61 


latter  is  not  essential,  spermatozoa  without  such,  an  appendage 
do  occur.  The  obvious  purpose  of  the  cilium  is  to  convey  the 
male  cell  to  the  ovum  through  a  fluid  medium — either  the  water 
in  which  the  ova  are  discharged  in  the  case  of  most  inverte- 
brates, or  through  the  fluids  that  overspread  the  surfaces  of  the 
female  generative  organs. 

The  Origin  of  the  Spermatozoon.— The  structures  devoted  to 
the  production  of  male  cells  (testes),  when  reduced  to  their  es- 


G5.— Spermatogenesis.  A— H,  isolated  spcrm-ccllH  of  tlie  rut,  sliowiuj;  the  development 
of  the  spermatozoon  and  the  <?radual  transformation  of  tli<-  niiclciiH  inUy  the  spermatozoon 

,  J,"  "^  semmal  granule  is  heing  (;ast  off  (afti-r  li.  fl.  l!rown).  I-  M,  sperm-cells 
or  an  P,lasrnf)ljranch.  Thf  nucleus  of  each  cell  divides  into  a  large  number  of  daughter- 
nuclei,  each  one  of  which  is  converted  into  the  rod  like  head  of  a  spermatozoon.  N,  traiis- 
v-erse  section  of  a  ripe  cell,  .showing  the  bundle  of  sijermatozoa  and  the  pa.ssive  nucleus 
i~t\.'  *  Semper).  O— S,  HrxTinatogenesis  in  the  earth-worm  :  O,  young  sperm-cell  ; 
K.  the  same  divided  intr»  four  ;  Q,  siK-rmatosphere  with  the  central  sperm  blastoijhore  ; 
K,  a  later  Hta-,'e  ;  8,  nearly  mature  sp(;rmatozoa.     (After  lilomfleld.) 

sentials,  consist  of  tubules,  of  great  Iciigth  in  mammals,  lined 
with   nucleated   epithelial  cells,   from    which,  by  a  series  of 


62  ANIMAL  PHYSIOLOGY. 

changes  figured  above,  a  general  idea  of  their  development  may 
be  obtained. 

It  will  be  observed  that  throughout  the  series  the  nucleus  of 
the  cell  is  in  every  case  preserved,  and  finally  becomes  the  head 
of  the  male  cell.  Once  more  we  are  led  to  see  the  importance 
of  this  structure  in  the  life  of  the  cell. 

Fertilization  of  the  Ovum. — The  spermatozoon,  lashing  its  way 
along,  when  it  meets  the  ovum,  enters  it  either  through  a  special 
minute  gateway  {micropyle) ,  or  if  this  be  not  present — as  it  is 
not  in  the  ova  of  all  animals — it  actually  penetrates  the  mem- 
branes and  substance  of  the  female  cell,  and  continues  active 
till  the  female  pronucleus  is  reached,  when  the  head  enters  and 
the  tail  is  absorbed  or  blends  with  the  female  cell.  The  nucleus 
of  the  male  cell  prior  to  union  with  the  nucleus  of  the  ovum 
undergoes  changes  similar  to  those  that  the  nucleus  of  the 
ovum  underwent,  and  thus  becomes  fitted  for  its  special  func- 
tions as  a  fertilizer ;  or  perhaps  it  would  be  more  correct  to  say 
that  these  altered  masses  of  nuclear  substance  mutually  fertil- 
ize each  other,  or  initiate  changes  the  one  in  the  other  which 
conjointly  result  in  the  subsequent  stages  of  the  development 
of  the  ovum.  The  altered  male  nucleus  {male  'pronucleus),  on 
reaching  the  female  pronucleus,  finds  it  somewhat  amseboid, 
a  condition  which  may  be  shared  in  some  degree  by  the  entire 


F.PNr-,    __. 

-M.PN. 

F.PNt 


Fig.  66.— Fertilization  of  ovum  of  a  mollusk  (Elysia  viridis).  A.  Ovum  sending  up  a  protu- 
berance to  meet  the  spermatozoon.  B.  Approach  of  male  pronucleus  to  meet  the  female 
pronucleus.    F.  PN,  female  pronucleus  ;  M.  PN,  male  pronucleus  ;  S,  spermatozoon. 

ovum.  The  resulting  union  gives  rise  to  the  new  nucleus  {seg- 
mentation nucleus),  which  is  to  control  the  future  destinies  of 
the  cell ;  while  the  cell  itself,  the  fertilized  ovum  {oosperm), 
enters  upon  new  and  marvelous  changes. 

In  reality  this  process  was  foreshadowed  in  the  dim  past  of 
the  history  of  living  things  by  the  conjugation  of  infusoria 
and  kindred  animal  and  vegetable  forms.  When  lower  forms 
(unicellular)  conjugate  they  become  somewhat  amoeboid  sooner 


REPRODUCTION.  63 

or  later,  and  division  of  cell  contents  results.  In  some  cases 
(septic  monads)  the. resulting  cell  may  burst  and  give  rise  to  a 
shower  of  animal  dust  visible  only  by  the  highest  powers  of  the 
microscope,  each  particle  of  which  proves  to  be  the  nucleus 
from  which  a  future  individual  arises. 

The  study  of  reproduction  thus  establishes  the  conception  of 
a  unity  of  method  throughout  the  animal  ^nd,  it  may  be  added, 
the  vegetable  kingdom,  for  reproduction  in  plants  is  in  all  main 
points  parallel  to  that  process  in  animals. 

But  why  that  costly  loss  of  protoplasm  by  polar  globules  ? 
For  the  present  we  shall  only  say  that  it  appears  necessary  to 
prevent  parthenogenesis  ;  or  at  least  to  balance  the  share  which 
the  male  and  female  elements  take  in  the  work  of  producing  a 
new  creature.  It  is  to  be  remembered  that  both  the  male  and 
female  lose  much  in  the  process — blood,  nervous  energy,  etc.,  in 
the  case  of  the  female,  while  the  male  furnishes  a  thousand-fold 
more  cells  than  are  used.  But  the  period  when  organisms  are 
best  fitted  for  reproduction  is  that  during  which  they  are  also 
most  vigorous,  and  can  best  afford  the  superfluous  drain  on 
their  energies. 

Segmentation  and  Subsequent  Changes. 

After  the  changes  described  in  the  last  chapter  a  new  epoch 
in  the  biological  history  of  the  ovum — now  the  oosperm  (or  fer- 
tilized egg) — begins.  A  very  distinct  nucleus  {segmentation 
nucleus)  again  appears,  and  the  cell  assumes  a  circular  outline. 
The  segmentation  or  division  of  the  ovum  into  usually  fairly 
equal  parts  now  commences.  This  process  can  be  best  watched 
in  the  microscopic  transparent  ova  of  aquatic  animals  which 
undergo  perfect  development  up  to  a  certain  advanced  stage 
in  the  ordinary  water  of  the  ocean,  river,  lake,  etc.,  in  which 
the  adult  lives. 

Segmentation  among  invertebrates  will  be  first  studied,  and 
for  tliis  purpose  an  ovum  in  which  the  changes  are  of  a  direct 
and  uncomplicated  nature  will  be  chosen. 

The  following  figures  and  descriptions  apply  to  a  mollusk 
( Elysia  v  i  rid  is).  We  distinguish  in  ova  resting  stages  and  stages 
of  activity.  It  is  not,  however,  to  be  supposed  tliat  absolute 
rest  ever  characterizes  any  living  form,  or  that  nothing  is  tran- 
spiring because  all  seems  quiet  in  these  little  biological  worlds  ; 
for  we  have  already  seen  reason  for  believing  that  life  and  in- 
cessant molecular  activity  are  inseparable.     It  may  be  that,  in 


64 


ANIMAL  PHYSIOLOGY. 


the  case  of  resting  ova,  changes  of  a  more  active  character  than 
usual  are  going  on  in  their  molecular  constitution  ;  but,  on  the 
other  hand,  there  may  be  really  a  diminution  of  these  activities 
in  correspondence  with  the  law  of  rhythm.  This  seems  the 
more  probable.     The  meaning,  however,  of  a  "  resting  stage  "  is 


Fig.  67.— Primitive  eggs  of  various  animals,  performing  amoeboid  movements  (very  much 
enlarged).  All  primitive  eggs  are  naked  cells,  capable  of  change  of  form.  Within  the 
dark,  finely  granulated  protoplasm  (egg-yelk)  lies  a  large  vesicular  kernel  (the  germ- 
vesicle),  and  in  the  latter  is  a  nucleolus  (germ-spot);  in  the  nucleolus  a  germ-point  (nucleo- 
linus)  is  often  visible.  Fig.  A  1—A  4.  The  primitive  egg  of  a  chalk  sponge  (Leuculmis 
echinus),  in  four  consecutive  conditions  of  motion.  Fig.  B  \—B  8.  The  primitive  egg  of  a 
hermit-crab  {Chondracanthus  cornutus),  in  eight  consecutive  conditions  of  motion  (after 
E.  Van  Beneden).  Fig.  C  1—C  5.  Primitive  egg  of  a  cat,  in  four  different  conditions  of 
motion  (after  Pfliiger).  Fig.  D.  Primitive  egg  of  a  trout.  Fig.  E.  Primitive  egg  of  a  hen. 
Fig.  F.  Primitive  human  egg.    (Haeckel.) 

the  obvious  oce  of  apparent  quiescence — cessation  of  all  kinds 
of  movement.  Then  ensues  rapidly  and  in  succession  the  fol- 
lowing series  of  transformations :  The  nucleolus  divides,  later 


REPRODUCTION. 


65 


the  nucleus,  into  two  parts.     These  new  nuclei  then  wander 
away  from  each  other  in  opposite  directions,  and,  losing  their 


Fig.  68.— Early  stages  of  segmentation  of  a  mollusk,  Elysia  viridis  (drawn  from  the  living 
egg).  A,  oosperm  in  state  of  rest  after  the  extrusion  of  the  polar  cells  ;  B,  the  nucleolus 
alone  has  divided  :  C,  the  nucleus  is  dividing  ;  D,  the  nucleus,  as  such,  has  disappeared, 
first  segmentation  furrow  appears  ;  E,  later  stage ;  F,  oosperm  divided  into  two  distinct 
segmentation  spheres,  the  clear  nuclear  space  in  the  center  of  the  aster  of  granules  is 
growing  larger  ;  G,  resting  stage  of  appressed  two  spheres  ;  H,  I,  similar  stages  in  the 
production  of  four  spheres  ;  K,  formation  of  eight-celled  stage.    (Haddon.) 

character  as  nuclei  and  nucleoli,  are  replaced  by  asters  {polar 
stars),  which  seem  to  arise  in  the  protoplasm  of  the  body  of 
the  cell,  and  which  are  in  close  juxtaposition  at  first,  but  later 
separate,  the  oosperm  becoming  amoeboid  in  one  region  at 
least.  A  groove,  which  gradually  deepens,  appears  on  the  sur- 
face, and  finally  divides  the  cell  into  two  halves,  which  at  once 
become  flattened  against  each  other.  The  nucleus  may  again 
be  recognized  in  the  center  of  each  jjolar  star,  while  a  new  nu- 
cleolus also  reappears  within  the  nucleus,  when  again  a  brief 
period  of  rest  ensues.  In  the  division  and  reformation  of  the 
nucleus,  when  most  complicated  {karyokinesis),  the  changes 
may  be  generalized  as  consisting  of  division  and  segregation, 
followed  by  aggregation. 

The  subdivision  (segmentation)  of  the  cell,  after  the  quies- 
cence referred  to,  again  commences,  but  in  a  plane  at  right 
angles  to  the  first,  from  which  four  spheres  result,  again  to  be 
followed  by  the  resting  stage.  The  process  continues  in  the 
same  way,  so  that  there  is  a  progressive  increase  in  the  num- 
ber of  segments,  at  least  up  to  the  point  when  a  large  number 

6 


66 


ANIMAL  PHYSIOLOGY. 


has  been  formed.  This  is  rather  to  be  considered  as  a  type  of 
one  form  of  segmentation  than  as  applicable  to  all,  for  even 
at  this  early  stage  differences  are  to  be  noted  in  the  mode  of 
segmentation  which  characterize  effectually  certain  groups  of 
animals ;  but  in  all  there  is  segmentation,  and  that  segmenta- 
tion is  rhythmical. 


Fig.  69.— The  cleavage  of  a  frog's  egg  (10  times  enlarged).  A,  the  parent-cell ;  B,  the  two 
first  cleavage-cells  ;  C,  4  cells  ;  D,  8  cells  (4  animal  and  4  vegetative) ;  E,  12  cells  (8  animal 
and  4  vegetative) ;  F,  16  cells  (8  animal  and  8  vegetative) ;  G,  34  cells  (16  animal  and  8 
vegetative) ;  H,  .82  cells  ;  /,  48  cells  ;  K,  64  cells  ;  L,  96  cleavage-cells  ;  M,  160  cleavage- 
cells  (128  animal  and  32  vegetative).    (Haeckel.) 

Segmentation  results  in  the  formation  of  a  multicellular 
aggregation  which,  sooner  or  later,  incloses  a  central  cavity 
{segmentation  cavity,  hlastocele).  Usually  this  cell  aggrega- 
tion {hlastula,  hlasto sphere)  is  reduced  to  a  single  layer  of  in- 
vesting cells. 

The  Gastrula. — Ensuing  on  the  changes  just  described  are 
others,  which  result  in  the  formation  of  the  gastrula,  a  form  of 
cell  aggregation  of  great  interest  from  its  resemblance  to  the 
Hydra  and  similar  forms,  which  constitute  in  themselves  inde- 
pendent animals  that  never  pass  beyond  that  stage.  The  blas- 
tula  becomes  flattened  at  one  pole,  then  depressed,  the  cells  at 


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REPRODUCTION.  67 

this  region  becoming  more  columnar  {histological  differentia- 
tion).   This  depression  (i?M'agma^ion)  deepens  until  a  cavity  is 


Fig.  70.— Blastula  and  gastrula  of  amphio.xus  iClaus,  after  Hatschek).  A,  blastula  with  flat- 
tened lower  pole  of  larger  cells ;  B,  comnieueing  invagination  ;  C,  gastrulation  completed': 
the  blastopore  is  still  widely  open,  and  one  of  the  two  hinder-pole  mesoderm  cells  is  seen 
at  its  ventral  lip.    The  cilia  of  the  epiblast  cells  are  not  represented.  " 

formed  (as  when  a  hollow  rubber  ball  is  thrust  in  at  one  part 
till  it  meets  the  opposite  wall),  in  consequence  of  which  a  two- 
layered  embryo  results,  in  which  we  recognize  the  primitive 
mouth  {blastopore)  and  digestive  cavity  {archenferon),  the 
outer  layer  {ectoderm)  being  usually  separated  from  the  inner 
{endoclerm)  by  the  almost  obliterated  segmentation  cavity. 
Such  a  form  may  be  provided  with  cilia,  be  very  actively  loco- 
motive, and  bear,  consequently,  the  greatest  resemblance  to  the 
permanent  forms  of  some  aquatic  animals. 

The  changes  by  which  the  segmented  oosperm  becomes  a 
gastrula  are  not  always  so  direct  and  simple  as  in  the  above- 
described  case,  but  the  behavior  of  the  cells  of  the  blastosphere 
may  be  hampered  by  a  burden  of  relatively  foreign  matter,  in 
the  form  of  food-yelk,  in  certain  instances ;  so  much  so  is  this 
the  case  that  distinct  modes  of  gastrula  formation  may  be  rec- 
ognized as  dependent  on  the  quantity  and  arrangement  of  food- 
yelk.  These  we  shall  pass  by  as  being  somewhat  too  compli- 
cated for  our  purpose,  and  we  return  to  the  egg  of  the  bird. 

The  Hen's  Egg. — By  far  the  larger  part  of  the  hen's  egg  is 
made  up  of  yelk  ;  but  just  beneath  the  vitelline  membrane  a 
small,  circular,  whitish  body,  aT)out  four  millimetres  in  diame- 
ter, which  always  floats  uppermost  in  every  portion  of  the  egg, 
may  be  seen.  This  disk  {blastoderm,  cicatricula)  in  the  fertilized 
egg  presents  an  outer  wliite  rim  {area  opaca),  within  which  is 
a  transparent  zone  {area  pellucida) ,  and  most  centrally  a  some- 
what elongated  structure,  which  marks  off  the  future  being 
itself  {emhryo).  All  of  these  parts  together  constitute  that  por- 
tion (hlasfoderrn)  of  the  fowl's  egg  which  is  alone  directly  con- 
cernf;d  in  reproduction,  all  the  rest  serving  for  nutrition  and 


68 


ANIMAL  PHYSIOLOGY. 


protection.     The  appearance  of  relative  opacity  in  some  of  the 
parts  marked  off  as  above  is  to  be  explained  by  thickening  in 

the  cell-layers  of  which  they  are 
composed. 

The  Origin  of  the  Fowl's  Egg. — 
The  ovary  of  a  young  but  mature 
hen  consists  of  a  mass  of  connect- 
ive tissue  {stroma),  abundantly 
supplied  with  blood-vessels,  from 
which  hang  the  capsules  which 
contain  the  ova  in  all  stages  of 
development,  so  that  the  whole 
suggests,  but  for  the  color,  a  bunch 
of  grapes  in  an  early  stage.  The 
ovum  at  first,  in  this  case  as  in  all 
others,  a  single  cell,  becomes  com- 
plex by  addition  of  other  cells  {dis- 
cus iDroligerus,  etc.),  which  go  to 
make  up  the  yelk.  All  the  other 
parts  of  the  hen's  Qgg  are  additions 
made  to  it,  as  explained  before,  in 
its  passage  down  the  oviduct.  The 
original  ovum  remains  as  the  blas- 
toderm, the  segmentation  of  which 
may  now  be  described  briefly,  its 
character  being  obvious  from  an 
examination  of  Fig.  72,  which  rep- 
resents a  surface  view  of  the  seg- 
menting fertilized  ovum  {oosperm). 
A  segmentation  cavity  appears 
early,  and  is  bounded  above  by  a 
single  layer  of  epiblast  cells  and 
below  by  a  single  layer  of  primi- 
tive hypoblast  cells,  which  latter 
is  soon  composed  of  several  layers. 
Fig.  7i.-Femaie  Reneiative  organs  of  while  the  Segmentation  cavity  dis- 

the  fo^^l  (atter  Dalton)     A,  ovarjs    Q„„ocn-o 
B,  Graafian  follicle,  from  which  the    appwd.!  b. 

^^^J"^^^^^^  of  The  blastoderm  of  an  unincu- 

o^itclSn'^wSdftreihSaSous  ^^ted    but  fertilized   egg  consists 

afe"f™drT'thirrportSln  of  a  layer  of  epiblastic  cells,  and 

which  the  fibrous  shell  membranes  i^encatli  this  a  mass   of    rouuded 

are  produced  ;  G,  fourth  portion  laid     '^^'-'■^'^'^'■^     ^      ^ 

open,  showing  the  egg  completely  ^ells,  arranged  irregularly  and  ly- 

formed  with  its  calcareous  shell ;  H,  '  =>  o  j  J 

canal  through  which  the  egg  is  ex-  ing  loosely  in  the  yelk,  constitut- 


REPRODUCTION. 


69 


Fig.  72.— Various  stages  in  the  segmentation  of  a  fowl's  egg  (Kolliker). 


ing  the  primitive  hypoblast.  After  incubation  for  a  couple  of 
hours,  these  cells  become  differentiated  into  a  lower  layer  of 
flattened  cells  {hypoblast),  with  mesoblastic  cells  scattered  be- 
tween the  epiblast  and  hypoblast.  It  is  noteworthy  that,  in  the 
bird,  segmentation  will  proceed  up  to  a  certain  stage  indepen- 
dently of  the  advent  of  the  male  cell,  apparently  indicating  a 
tendency  to  parthenogenesis. 


FlO.  73.— Portion  of  section  tiirough  an  uninoul)ated  fowl's  oosnenn  (after  Klein),  a,  epiblast 
W)mpo«efl  of  a  single  layer  of  columnar  cells  ;  h,  irregularly  disposed  lower  layer  cells  of 
the  primitive  hypoblast ;  r.  larger  formative  ceils  re.sting  on  white  yelk  ;  /,  arclienteron. 
The  8<^gmentation  cavity  lies  between  a  and  />,  and  is  nearly  obliterated. 


70 


ANIMAL   PHYSIOLOGY. 


The  fowl's  ovum  then  belongs  to  the  class,  a  portion  of  which 
alone  segments  and  develops  into  the  embryo  (meroblastic) ,  in 
contradistinction  to  what  happens  in  the  mammalian  ovum,  the 
whole  of  which  undergoes  division  (holoNasUc) ;  a  distinction 
which  is,  however,  superficial  rather  than  fundamental,  for  in 
reality  in  the  fowl's  egg  the  whole  of  the  original  ovum  does 


Fig.  74. — Sections  of  ovum  of  a  rabbit,  illustrating  formation  of  the  plastodermic  vesicle  (after 
E.  Van  Beneden).  A,  B,  C,  D,  are  ova  in  successive  stages  of  development,  ep,  zona  pellu- 
cida  ;  ecf,  ectomeres,  or  outer  cells  ;  ent,  entomeres,  or  inner  cells. 

segment.  This  holoblastic  character  of  the  mammalian  ovum 
and  its  resemblance  to  the  segmentation  of  those  invertebrate 
forms  previously  described  may  become  apparent  from  an  ex- 
amination of  the  accompanying  figures. 

We  shall  return  to  the  development  of  the  mammalian  ovum 
later  ;  in  the  mean  time  we  present  the  main  features  of  devel- 
opment in  the  bird. 

Remembering  that  the  development  of  the  embryo  proper 
takes  place  within  the  pellucid  area  only,  we  point  out  that  the 
area  opaca  gradually  extends  over  the  entire  ovum,  inclosing 


REPRODUCTION. 


n 


the  je\k,  so  that  the  original  disk  which  lay  like  a  watch-glass 
on  the  rest  of  the  ovum,  has  grown  into  a  sphere.  That  portion 
of  this  area  nearest  the  pellucid  zone  {area  vasculosa)  develops 


Fig.  75.— Diagrammatic  transverse  sections  through  a  hypothetical  mammal  oosperm  (Had- 
don).  A.  The  yelk  of  the  primitive  mammalian  oosperm  is  now  lost.  B.  Later  stage  ; 
the  non-embryonic  epiblast  has  grown  over  the  embryonic  area  to  form  the  covering  cells, 
ep,  epiblast  of  embryo  ;  ep\  epiblast  of  yelk-sac  ;  hy,  primitive  hypoblast ;  y.  s,  yelk-sac. 
or  blastodermic  vesicle. 


H 


blood-vessels  that  derive  the  food-supplies,  which  replenish  the 
blood  as  it  is  exhausted,  from  the  hypoblast  of  the  area  opaca. 

The  first  indications  of  future  structural  outlines  in  the 
embryo  is  the  formation  of  the  primitive  streak^sjo.  opaque  band 
in  the  long  diameter  of  the  pellu- 
cid area,  opaque  in  consequence 
of  cell  accummulation  in  that  re- 
gion. Very  soon  a  groove  {primi- 
tive groove)  extends  throughout 
this  band,  which  gradually  occu- 
pies a  more  central  position.  The 
relative  thickness  of  the  several 
parts  and  the  arrangement  of  cells 
may  be  gathered  from  Fig.  7(j. 
These  structures  are  only  tempo- 
rary, and  those  that  replace  them 
will  be  described  subsequently. 

We  have  thus  far  spoken  of 
cells  as  being  arranged  into  epi- 
bla.st,  hy[;oblast,  and  mesoblast. 
The  origin  of  the  first  two  has 
been  sufficiently  indicated.  The 
mesoblast  forms  the  interme<liate 
germinal  layer,  and  is  derived 
from  the  primitive  hypoblast, 
wliich  differentiates  into  a  stratum  of  flattened  cells,  situated 
below  the  others,  and  constituting  the  later  hypoblast,  and  in- 


j.  7fi.— Siir-face  view  of  pellucid  area  of 
hla,st<)derui  of  eighteen  hours  ( Foster  and 
Halfour).  y/,  medullary  folds;  mc,  med- 
ullary groove  ;  pr,  primitive  groove. 


72 


ANIMAL   PHYSIOLOGY. 


termediate  less  closely  arranged  cells,  termed,  from  tlieir  posi- 
tion, mesoblast. 

It  will  be  noticed  that  all  future  growth  of  the  embryo  be- 
gins axially,  at  least  in  the  early  stages  of  its  development. 

As  the  subsequent  growth  and  advance  of  the  embryo  de- 
pend on  an  abundant  and  suitable  nutritive  supply,  we  must 
now  turn  to  those  arrangements  which  are  temporary  and  of 
subordinate  importance,  but  still  for  the  time  essential  to  devel- 
opment. 

Embryonic  Membranes  of  Birds. 

It  will  be  borne  in  mind  throughout  that  the  chief  food-sup- 
ply for  the  embryo  bird  is  derived  from  the  yelk ;  and,  as  would 


-.      «/ 


\--P2^ 


■vl 


■PP 


Figs.  77-79.— A  series  of  diagrams  intended  to  facilitate  the  comprehension  of  the  relations  of 
the  membranes  to  other  parts  (after  Foster  and  Balfour).  A,  B,  C,  D,  E,  F  are  vertical 
sections  in  the  long  axis  of  the  embryo  at  different  periods,  showing  the  stages  of  develop- 
ment of  the  amnion  and  of  the  yelk-sac.  I,  II,  III,  IV  are  transverse  sections  at  about  the 
same  stages  of  development,  i,  ii,  iii,  posterior  part  of  longitudinal  section,  to  illustrate 
three  stages  in  formation  of  the  allantois.  e,  embryo  ;  y,  yelk  ;  pp,  pleuroperitoneal  cav- 
ity ;  vt,  vitelUne  membrane  of  amniotic  fold ;  al,  allantois ;  a,  amnion ;  a',  alimentary 
canal. 

be  expected,  the  older  the  embryo  the  smaller  the  yelk,  or,  as  it 
is  now  called  when  limited  by  the  embryonic  membranes,  the 
yelk-sac  {umbilical  vesicle  of  the  mammalian  embryo).  The 
manner  in  which  this  takes  place  will  appear  upon  an  inspec- 
tion of  the  accompanying  figures. 

Very  early  in  the  history  of  the  embryo  two  eminences,  the 
head  and  the  tail  folds,  arise,  and,  curving  over  toward  each 


REPRODUCTION. 

trc 


73 


pp- 


FiG.  78. 


IV 


I—  PP 


74 


ANIMAL  PHYSIOLOGY. 


other,  meet  after  being  joined  by  corresponding  lateral  folds. 
Fusion  and  absorption  result  at  tliis  meeting-point,  in  the 
inclosure  of  one  cavity  and  the  blending  of  two  others.     These 


N.C. 


Fig.  80. —Diagrammatic  longitudinal  section  through  the  axis  of  an  embryo  chick  (after  Foster 
and  Balfour).  N.  C,  Neural  canal ;  CVi,  notochord  ;  Fg,  foregut ;  F.  So,  somatopleure  ; 
F.  Sp,  splanchnopleure  ;  Sp,  splanchnopleure,  forming  lower  wall  of  foregut ;  Ht,  heart ; 
2)p,  pleuroperitoneal  cavity  ;  Am,  amniotic  fold  ;  F,  epiblast ;  M,  mesoblast ;  H,  hypoblast. 


folds  constitute  the  amniotic  membranes,  the  inner  of  which 
forms  the  true  amnion,  the  outer  the  false  amnion  {serous  mem- 
brane, sub  zonal  membrane).  Within  the  amnion  proper  is  the 
amniotic  cavity  filled  with  fluid  {liquor  amnii),  while  the  space 
between  the  true  and  false  amniotic  folds,  which  gradually  in- 
creases in  size  as  the  yelk-sac  diminishes,  forms  the  pleuro- 
peritoneal cavity,  body  cavity,  or  coelom.  The  amniotic  cavity 
also  extends,  so  that  the  embryo  is  surrounded  by  it  or  lies 
centrally  within  it.  The  enlargement  of  the  coelom  and  exten- 
sion of  the  false  amniotic  folds  lead  finally  to  a  similar  meeting 
and  fusion  like  that  which  occurred  in  the  formation  of  the  true 
amniotic  cavity.  The  yelk-sac,  gradually  lessening,  is  at  last 
withdrawn  into  the  body  of  the  embryo. 

Fig.  80  shows  how  the  amniotic  head  fold  arises,  from  a 
budding  out  of  the  epiblast  and  mesoblast  at  a  point  where  the 
original  cell  layers  of  the  embryo  have  separated  into  two  folds, 
the  somatopleure  or  body  fold  and  the  splanchnopleure  or  vis- 
ceral fold,  owing  to  a  division  or  cleavage  of  the  mesoblast 
toward  the  long  axis  of  the  body.  Remembering  this,  it  is 
always  easy  to  determine  by  a  diagram  the  composition  of  any 
one  of  the  membranes  or  folds  of  the  embryo,  for  the  compo- 
nents must  be  epiblast,  mesoblast,  or  hypoblast ;  thus,  the 
splanchnopleure  is  made  up  of  hypoblast  internally  and  meso- 
blast externally — a  principle  of  great  significance,  since,  as  will 
be  learned  later,  all  the  tissues  of  the  body  may  be  classified 
simply,  and  at  the  same  time  scientifically,  according  to  their 
embryological  origin. 


REPRODUCTION.  75 

The  allaniois  is  a  structure  of  much  physiological  impor- 
tance. It  arises  at  the  same  time  as  the  amniotic  folds  are 
forming,  by  a  budding  or  protrusion  of  the  hind-gut  into  the 


Fig.  81. — Diagrammatic  longitudinal  section  of  a  chick  of  the  fourth  day  (after  Allen  Thom- 
son), ep.  epibla.st ;  hy,  hypoblast :  sm,  somatoplem-e  ;  vm,  splauchnopleure  ;  «/,  />/,  folds 
of  the  amnion  :  pp.  pleuroperitoneal  cavitj' ;  aw,  cavity  of  the  amnion  ;  «/,  allantois  ;  a, 
position  of  the  future  anus  ;  /i,  heart ;  i,  intestine  ;  vi,  vitelline  duct ;  ys,  yelk  ;  s,  foregut ; 
»/i,  position  of  the  mouth  ;  rwe,  mesentery. 

pleuro-peritoneal  cavity,  and  hence  consists  of  an  outgrowth 
of  mesoblast  lined  by  hypoblast. 

The  outer  membrane  of  the  allantois  fuses  with  the  subzo- 
nal  (serous)  membrane,  and,  with  the  latter  extending  beyond 
the  yelk-sac,  incloses  the  albumen  of  the  egg  in  a  space  termed 


Fio.  82.— A.  Diagrammatic  longitudinal  section  through  the  egg  of  a  fowl.  B.  Detail  of  por- 
tion of  sai/i"!  at  a  time  when  the  allant<jis  rea<;hfd  the  spot  marked  x  in  A  (after  Duval). 
(il.  cavity  of  allanUji.s  ;  a/6,  albuin<;n  ;  alt,  mesenteron  ;  al.  hi/,  hypoblastic  epithelium  of 
allantois  ;  (il.  rn,  inesfjblast  of  allanti'jiK  ;  urn,  cavity  of  amnion  ;  h,  hlood-vcssel ;  eiiih, 
emliryo  ;  fp,  epihiast  <>t  ouUt  layer  of  amnion  (serous  membrane)  ;  I'/i.  nin,  ei)il)lastic 
ej)itlieliurn  of  inner  layer  of  amniiin  larnnion  proper) :  in.,  am,  mesoblastic!  layi-i-  of  latter  ; 
ill.  ejfjf-shell  ;  num.  somatic  mesoblast  of  outer  layer  of  amnion  ;  v.  in,  vitelliin'  membrane  ; 
U-.  jxtint  where  the  mesoblastic  tissue  of  the  a\\a,uUAa  fuses  with  that  of  tlie  serous  mem- 
brane. 


76 


ANIMAL  PHYSIOLOGY. 


the  placental  sac  by  Duval,  who  has  recently  described  this  pro- 
cess. Villi,  or  tubular  vascular  outgrowths,  spring  from  the 
lining  of  this  sac  and  serve  to  convey  the  absorbed  and  prob- 
ably altered  albumen  to  the  embryo,  in  which  process  of  vas- 
cular transport  of  nourishment  the  yelk-sac,  that  also  abounds 
in  blood-vessels  as  well  as  the  allantois,  takes  part.  The 
physiological  import  of  the  various  structures  above  described 
will  be  considered  more  fully  later.  At  this  point  a  compari- 
son of  the  formation  of  the  corresponding  parts  in  mammals 
will  be  undertaken. 

The  Fcetal  (Embryonic)  Membranes  of  Mammals. 

The  differences  between  the  development  of  the  egg  mem- 
branes of  mammals  and  birds  are  chiefly  such  as  result  from 


Fib.  83.  Fig.  84. 

Fig.  8.3. — Diagrammatic  longitudinal  section  of  oosperm  of  rabbit  at  an  advanced  stage  of 
pregnancy  (Kfilliker,  after  Bischoff ).  a,  amnion  ;  al,  allantois  with  its  blood-vessels ;  e, 
embryo ;  ds,  yelk-sac  ;  ed,  ed\  ed",  hypoblastic  epithelium  of  the  3'elk-sac  and  its  stalk 
(umbilical  vesicle  and  cord) ;  fd,  vascular  mesoblastic  membrane  of  the  umbilical  cord 
and  vesicle  ;  p,  placental  villi  formed  by  the  allantois  and  subzonal  membrane  ;  r,  space 
filled  with  fluid  between  the  amnion,  the  aUantois,  and  the  yelk-sac  ;  st,  sinus  terminalis 
(marginal  vitelline  blood-vessel) ;  it,  urachus,  or  stalk  of  the  allantois. 

Fig.  8-t. — Diagrammatic  dorsal  view  of  an  embryo  rabbit  with  its  membranes  at  the  stage  of 
nine  somites  (Haddon,  after  Van  Beneden  and  Julini.  cd,  allantois,  showing  from  behind 
the  tail  fold  of  the  embryo  ;  am.  anterior  border  of  true  amnion  ;  a.  v.  area  vaseulosa,  the 
outer  border  of  which  indicates  the  farthest  extension  of  the  mesoblast ;  bl,  blastoderm, 
here  consisting  only  of  epiblast  and  hypoblast  ;  o.  m.  r,  omphalo-mesenteric  or  vitelline 
veins  ;  p.  am,  proamnion  ;  pi,  non-vascular  epiblastic  villi  of  the  future  placenta  ;  s.  t,  si- 
nus terminalis. 

the  absence  in  the  former  of  an  egg-shell  and  its  membranes, 
and  of  yelk  and  albumen.  The  mammalian  ovum  is  inclosed 
by  a  zona  radiata  (zona  pellucida)  surrounding  another  very 
delicate  covering  (Fig.  58). 

The  growth  of  the  blastodermic  vesicle  (yelk-sac)  is  rapid. 


REPRODUCTION. 


77 


and,  being  filled  with  fluid,  the  zona  is  thinned  and  soon  disap- 
pears. 

The  germinal  area  alone  is  made  up  of  three  layers  of  cells 
(Fig.  104),  the  rest  of  the  upper  part  of  the  oosperm  being  lined 
■with  epiblast  and  hypoblast,  while  the  lower  zone  of  the  yelk- 
sac  consists  of  epiblast  only. 

Simple,  non-vascular  villi,  serving  to  attach  the  embryo 
to  the  uterine  walls,  usually  project  from  the  epiblast  of  the 
subzonal  membrane.  In  the  rabbit  they  do  not  occur  every- 
where, but  only  in  that  region  of  the  epiblast  beneath  which  the 
mesoblast  does  not  extend,  with  the  exception  of  a  patch  which 
soon  appears  and  demarkates  the  site  of  the  future  placenta. 

The  extension  of  the  mesoblast  takes  place  in  every  direction 
from  the  embryo  except  directly  around  the  head ;  but  the  two 


Fig.  85.— Diagrammatic  median  vertical  longiturlinal  section.s  through  embryo  ral)l)it  (Had- 
don.  after  Van  Bi-neden  and  Julin).  A.  Section  through  embryo  of  Fig.  H4.  \i.  Section 
tlirough  f  nibryf)  of  eleven  days,  al,  allautois  ;  arn,  amnion  ;  a.  ins,  anterior  median  plate 
of  mi'soblast,  formed  by  the  junction  of  the  anterior  horns  of  the  area  opaca  ;  ti.  pt,  area 
placentalis  ;  a.  r.  area  vasculosa  ;  ch,  chorion  ;  cw,  c(]Blom  of  embryo  ;  cw',  extra-embry- 
onic portifin  of  the  body-cavity  ;  eyj,  epiblast ;  h;/,  hypoblast ;  m.  uusplit  mesoblast  ;  o.  «, 
oriflo-  of  amnion  ;  pi,  |>lacenta  ;  jjrn,  a,  proamnion  ;  g.  (,  sinus  terminalis  ;  v,  epiblastic 
villi  of  blastodermic  vesicle. 


expansions  of  the  mesoblast  which  mark  out  this  area  extend 
for  some  di.stance  in  front  of  the  head,  and  ultimately  unite  ; 
so  that  immediately  in  front  of  the  head  there  is  a  circular 
region  in  wliich  tlio  Ijlastodei-m  consists  of  epiblast  and  hypo- 


78  ANIMAL  PHYSIOLOGY. 

blast  only,  forming  a  cavity  into  which  the  anterior  part  of  the 
embryo  early  projects  (pro-amnion). 

The  true  amnion  arises  only  from  the  posterior  end  of  the 
embryo,  and,  extending  over  in  a  forward  direction,  meets  the 
raised  projection  of  the  pro-amnion  with  which  it  fuses. 

The  amniotic  cavity  becomes  one  with  that  space  (extra-em- 
bryonic pleuro-peritoneal  cavity)  arising  from  the  cleavage  of 


A.pL 


Fig.  86.— Foetal  envelopes  of  a  rabbit  embryo  (Minot,  after  Van  Beneden  and  Julin).  Later 
stage  than  Fig.  85  B.  The  amnion  has  become  fused  with  the  blastoderm  in  front  of  the 
embryo,  and  its  cavity  is  therefore  continuous  with  the  extra-embryonic  portion  of  the 
body-cavity  in  front  of  the  embryo.  Al,  allantois  ;  «m,  amnion  ;  am',  portion  of  the 
amnion  united  with  the  walls  of  the  allantois  ;  A.  pi,  area  placentalis  ;  Av,  area  vasculosa  ; 
Ch,  chorion  ;  Cce.  coelom  or  body-cavity  ;  Cce",  extra-embryonic  portion  of  the  body- 
cavity  ;  Coel,  anterior  portion  of  the  same,  produced  by  the  fusion  of  the  cavity  of  the 
amnion  with  that  of  the  anterior  portion  of  the  area  opaca  ;  Ec,  epiblast ;  En,  alimentary 
canal  of  the  embryo  ;  Ent,  hypoblast ;  PI,  placenta  ;  pro.  A,  proamnion  ;  T,  sinus  ter- 
minalis  ;  V,  villi  of  blastodermic  vesicle  ;  Y,  cavity  of  blastodermic  vesicle. 

the  mesoblast,  which  now  advances  beyond  the  head  of  the  em- 
bryo and  the  pro-amnion.  The  pro-amnion  by  gradual  atrophy 
gives  place  to  the  true  amnion. 

At  about  the  same  period  as  these  events  are  transpiring  the 
vascular  yelk-sac  has  become  smaller,  and  the  allantois  with  its 
abundant  supply  of  blood-vessels  is  becoming  more  xjrominent, 
and  extending  between  the  amnion  and  subzonal  membrane. 

The  formation  of  the  chorion  marks  an  important  step  in 
the  development  of  mammals  in  which  it  plays  an  important 
functional  part.  It  is  the  result  of  the  fusion  of  the  allantois, 
which  is  highly  vascular,  with  the  subzonal  membrane,  the  villi 
of  which  now  become  themselves  vascular  and  more  complex 
in  other  respects. 

An  interesting  resemblance  to  birds  has  been  observed  (by 
Osborn)  in   the   opossum.     When  the  allantois  is  small  the 


REPRODUCTION. 


Y9 


Fig.  87.— Embryo  of  dog,  twenty-flve  days  old,  opened  on  the  ventral  side.  Chest  and  ven- 
tral walls  have  been  removed,  a,  nose-pits  ;  6,  eyes  :  c,  under-jaw  (first  gill-arch) ;  d, 
second  gill-arch;  e.f,g,  h,  heart  (e,  right,  f,  left  auricle;  g,  right,  7i,  left  ventricle);  i, 
aorta  (origin  of);  kk\  liver  (in  the  middle  between  the  two  lobes  is  the  cut  yelk-vein); 
I,  stomach  ;  tn,  intestine  ;  n,  yelk-sac  ;  o,  primitive  kidneys  :  p,  allantois  ;  q,  fore-limbs  ; 
/i,  hind-limbs.  The  crooked  embryo  has  been  stretched  straight.  (Haeckel,  after 
Bischoff.) 


'Ji-^-jp 


Fio.  88.— Dlajfram  of  an  embryo  showing  the  relations  of  the  vascular  allantoiR  to  the  vllU  of 
the  chorion  'Ca<liat).  p,  embryo  lying  in  the  cavity  of  the  amnion  ;  us,  yelk-sac  ;  a/,  al- 
laDU.il8  ;  A.  V,  allantoic  ve»M*ela  dipping  into  the  vllU  of  the  chorion  ;  ch,  cnorion. 


ANIMAL  PHYSIOLOGY. 


blastodermic  vesicle  (yelk-sac)  lias  vascular  villi,  whicli  in  all 
probability  not  only  serve  the  purpose  of  attaching  the  embryo 
to  the  uterine  wall  but  derive  nourishment,  not  as  in  birds,  from 
the  albumen  of  the  ovum,  but  directly  in  some  way  from  the 
uterine  wall  of  the  mother.     It  will  be  remembered  that  the 

opossum  ranks  low  in  the 
mammalian  scale,  so  that  this 
resemblance  is  the  more  signifi- 
cant from  an  evolutionary  point 
of  view. 

The  term  chorion  is  now  re- 
stricted to  those  regions  of  the 
subzonal  membrane  to  which 
either  the  yelk-sac  or  the  allan- 
tois  is  attached.  The  former 
zone  has  been  distinguished  as 
the  false  chorion  and  the  latter 
as  the  true  chorion.  In  the 
rabbit  the  false  chorion  is  very 
large  (Fig.  83),  and  the  (placen- 
tal) chorion  very  small  in  com- 
parison, but  the  reverse  is  the 
case  in  most  mammals.  It  will 
be  noted  that  in  both  birds  and 
mammals  the  allantois  is  a  nu- 
tritive organ.  Usually  the  more  prominent  and  persistent  the 
yelk-sac,  the  less  so  the  allantois,  and  vice  versa;  they  are 
plainly  supplementary  organs. 

The  Placenta. — This  structure,  which  varies  greatly  in  com- 
plexity, may  be  regarded  as  the  result  of  the  union  of  structures 
existing  for  a  longer  or  shorter  period,  free  and  largely  inde- 
pendent of  each  other.  With  evolution  there  is  differentiation 
and  complication,  so  that  the  placenta  usually  marks  the  site 
where  structures  have  met  and  fused,  differentiating  a  new 
organ;  while  corresponding  atrophy,  obliteration,  and  fusion 
take  place  in  other  regions. 

All  placentas  are  highly  vascular,  all  are  villous,  all  dis- 
charge similar  functions  in  providing  the  embryo  with  nourish- 
ment and  eliminating  the  waste  of  its  cell-life  (metabolism). 
In  structural  details  they  are  so  different  that  classifications  of 
mammals  have  been  founded  upon  their  resemblances  and  dif- 
ferences.    These  will  now  be  briefly  described. 

In  marsupials  the  yelk-sac  is  both  large  and  vascular ;  the 


Fig.  89. — Diagram  of  the  foetal  membranes  of 
the  Virginian  opossum  (Haddon,  after  Os- 
born).  Two  villi  are  shown  greatly  en- 
larged. The  processes  of  the  cells,  which 
have  been  exaggerated,  doubtless  corre- 
spond to  the  pseudopodia  described  by 
Caldwell,  al,  allantois ;  ani,  amn'on  ;  s.  t, 
sinus  terminalis  ;  s.  z,  subzonal  mem- 
brane ;  V,  villi  on  the  sulazonal  membrane 
in  the  region  of  the  yelk-sac  ;  ys,  yelk 
sac.  The  vascular  splanchnopleure  (hy- 
poblast and  mesoblast)  is  indicated  by 
the  black  line. 


REPRODUCTION.  81 

allantois  small  but  vascular ;  the  former  is  said  (Owen)  to  be 
attached  to  the  subzoual  membrane,  the  latter  not ;  but  no  villi, 
and  consequently  no  true  chorion,  is  developed.  All  mammals 
other  than  the  monotremes  and  marsupials  have  a  true  allan- 
toic placenta. 

The  Discoidal  Placenta. — This  form  of  placenta  is  that  existing 
in  the  rodentia,  insectivora,  and  cheiroptera.  The  condition 
found  in  the  rabbit  is  that  which  has  been  most  studied.  The 
relation  of  parts  is  shown  in  Fig.  83. 

The  uterus  of  the  rodent  is  two-horned ;  so  we  find  in  gen- 
eral several  embryos  in  each  horn  in  the  pregnant  rabbit.  They 
ate  functionally  independent,  each  having  its  own  set  of  mem- 
branes. It  will  be  observed  from  the  figure  that  the  true  vil- 
lous chorion  is  confined*  to  a  comparatively  small  region ;  there 
is,  however,  in  addition  a  false  chorion  without  villi,  but  highly 
vascular.  This  blending  of  forms  of  placentation  which  exist 
separately  in  different  groups  of  animals  is  significant.  In  the 
rabbit,  at  a  later  stage,  there  is  considerable  intermingling  of 
foetal  and  maternal  parts. 

The  Metadiscoidal  Placenta.  —  This  type,  which,  in  general 
naked-eye  appearances,  greatly  resembles  the  former,  is  found 
in  man  and  the  apes.  The  condition  of  things  in  man  is  by  no 
means  as  well  understood  as  in  the  lower  mammals,  especially 
in  the  early  stages  ;  so  that,  while  the  following  account  is  that 
usually  given  in  works  on  embryology,  the  student  may  as  well 
understand  that  our  knowledge  of  human  embryology  in  the 
very  earliest  stages  is  incomplete  and  partly  conjectural.  The 
reason  of  this  is  obvious :  specimens  for  examination  depending 
on  accidents  giving  rise  to  abortion  or  sudden  death,  often  not 
reaching  the  laboratory  in  a  condition  permitting  of  trust- 
worthy inferences. 

It  is  definitely  known  that  the  ovum,  which  is  usually  fer- 
tilized in  the  oviduct  (Fallojnan  tube),  on  entering  the  uterus 
becomes  adherent  to  its  wall  and  encapsuled.  The  mucous 
membrane  of  the  uterus  is  known  to  undergo  changes,  its  com- 
ponent parts  increasing  by  cell  multiplication,  becoming  in- 
tensely vascular  and  functionally  more  active.  The  general 
mucous  surface  shares  in  this,  and  is  termed  the  decidua  vera  ; 
but  the  locality  where  the  ovum  lodges  is  the  seat  of  the  great- 
est manifestation  of  exalted  activity,  and  is  termed  the  decidua 
■serotina;  while  the  part  believed  to  have  invested  the  ovum  by 
fused  gi-owths  from  the  junction  of  the  decidua  vera  and  sero- 
tina is  the  decidua  reflexa. 


82 


ANIMAL  PHYSIOLOGY. 


The  decidua  serotina  and  reflexa  thus  become  the  outermost 
of  all  the  coverings  of  the  ovum.  These  and  some  other  devel- 
opments are  figured  below.  It  is  to  be  remembered,  however, 
that  they  are  highly  diagrammatic,  and  represent  a  mixture 


Fio.  90.  —Series  of  diagrams  representing  the  relations  of  the  decidua  to  the  ovum,  at  different 
periods,  in  the  human  subject.  The  decidua  are  dark,  the  ovum  shaded  transversely.  In 
4  antl  5  the  chorionic  vascular  processes  are  figured  (after  Dalton).  1.  Ovum  resting  on 
the  decidua  serotina  ;  2.  Decidua  reflexa  growing  round  the  ovum  ;  3.  Completion  of  the 
decidua  around  the  ovum  ;  4.  Villi,  growing  out  all  around  the  chorion  ;  5.  The  villi,  spe- 
cially developed  at  the  site  of  the  future  placenta,  having  atrophied  elsewhere. 

of  inferences  based,  some  of  them,  on  actual  observation  and 
others  on  analogy,  etc. 

The  figures  will  convey  some  information,  though  appear- 
ances in  all  such  cases  must  be  interpreted  cautiously  for  the 
reasons  already  mentioned. 

During  the  first  fourteen  days  villi  appear  over  the  whole 
surface  of  the  ovum ;  about  this  fact  there  is  no  doubt.  At 
the  end  of  the  first  month  of  foetal  life,  a  complete  chorion 
has  been  formed,  owing,  it  would  seem,  to  the  growth  of  the 
allantois  (its  mesoblast  only)  beneath  the  whole  surface  of  the 
subzonal  membrane.  From  the  chorionic  surface  vascular  pro- 
cesses clothed  with  epithelium  project  like  the  i^lush  of  velvet. 


REPRODUCTION. 


83 


The  allantois  is  compressed  and  devoid  of  a  cavity,  but  abun- 
dantly supplied  with  blood-vessels  by  the  allantoic  arteries  and 


Fig.  91.— Vascular  system  of  the  human  foetus,  represented  diagrammatically  (Huxley). 
H.  heart ;  TA,  aortic  trunk  ;  c,  common  carotid  artery  ;  c',  external  carotid  artery  ;  c''. 
Internal  carotid  artery  ;  s,  subclavian  artery  :  v,  vertebral  artery  ;  1,  3,  3,  4,  5,  aortic 
arches  ;  .4',  dorsal  aorta  :  o,  omphalo-mesenteric  artery  ;  dv.  vitelline  duct ;  o',  omphalo- 
mesenteric vein  ;  v\  umbilical  vesicle  ;  rp,  portal  vein  ;  Z,,  liver  ;  u,  m.  umbilical  arteries  ; 
u".  m",  their  endings  in  the  placenta  :  u',  umbilical  vein  ;  Du,  ductus  venosus  ;  vh,  hepatic 
vein  ;  cv,  inferior  vena  cava ;  iu7.  iliac  veins ;  az,  vena  azygos  ;  vc',  posterior  cardinal 
vein  ;  DC\  duct  of  Cuvier  ;  P,  lung. 

veins,  which  of  course  terminate  in  capillaries  in  the  villi. 
Compare  the  whole  series  of  figures. 


Fio.  92.  —Human  ova  during  early  stages  of  development.  A  and  15,  front  and  side  view  of  an 
ovum  supposed  to  be  aljout  thirteen  days  old  ;  e,  embryonic  area  (Quain,  after  Reichert) ; 
C.  ovum  of  four  to  five  weeks,  showing  the  general  structure  of  the  ovum  before  formation 
of  the  placenta.  Part  of  the  wall  of  the  ovum  is  removed  to  show  the  embryo  in  position 
lafter  Allen  Thomson). 

At  this  stage  the  condition  of  the  chorion  suggests  the  type 
of  the  diffuse  placenta  which  is  normal  for  certain  groups  of 
animals,  as  will  presently  be  learned. 

The  subsequent  changes  are  much  better  understood,   for 


84 


ANIMAL  PHYSIOLOGY. 


parts  are  in  general  no  longer  microscopic  but  of  considerable 
size,  and  tbeir  real  structure  less  readily  obscured  or  obliterated. 
The  amniotic  cavity  continues  to  enlarge  by  growth  of  the 
walls  of  the  amnion  and  is  kept  filled  with  a  fluid ;  the  yelk-sac 
is  now  very  small ;  the  decidua  reflexa  becomes  almost  non- 
vascular, and  fuses  finally  with  the  decidua  vera  and  the  cho- 
rion, which  except  at  one  part  has  ceased  to  be  villous  and  vas- 
cular ;  so  that  becoming  thinner  and  thinner  with  the  advance 
of  pregnancy,  the  single  membrane,  arising  practically  from 
this  fusion  of  several,  is  of  a  low  type  of  structure,  the  result  of 


Fig.  93.— Human  embryo,  twelve  weeks  old,  with  its  coverings  ;  natural  size.  The  navel-cord 
passes  from  the  navel  to  the  placenta,  b,  amnion  ;  c,  chorion  ;  d,  placenta  ;  d',  remains 
of  tufts  on  the  smooth  chorion  ;  /,  decidua  reflexa  (inner) ;  g,  decidua  vera  (outer).  (Haec- 
kel  after  Bemhard  Schultze.) 


gradual  degeneration,  as  the  role  they  once  played  was  taken 
up  by  other  parts. 

But  of  paramount  importance  is  the  formation  of  the  pZa- 
centa.  The  chorion  ceases  to  be  vascular  except  at  the  spot  at 
which  the  villi  not  only  remain,  but  become  more  vascular  and 
branch  into  arborescent  forms  of  considerable  complexity.  It 
is  discoidal  in  form,  made  up  of  a  foetal  part  just  described  and 


REPRODUCTION. 


85 


a  maternal  part,  the  decidua  serotina,  the  two  becoming  blended 
so  that  the  removal  of  one  involves  that  of  more  or  less  of  the 
others.  The  connection  of  parts  is  far  closer  than  that  described 
for  the  rabbit ;  and,  even  with  the  preparation  that  Nature  makes 
for  the  final  separation  of  the  placenta  from  both  foetus  and 


Fig.  94.— Diagram  illustrating  the  decidua,  placenta,  etc.  (after  Lifgeois),  e,  embryo  ; 
J.  intestine  ;  p.  pedicle  of  the  umbilical  vesicle  :  !(.  v.  umbilical  vesicle  ;  a.  amnion  ;  cli, 
chorion;  i'.  t,  vascular  tufts  of  the  chorion,  constituting  the  fcetal  portion  of  the  placenta; 
m.  p,  maternal  portion  of  the  placenta  ;  d.  i\  decidua  vera  ;  d.  r.  decidua  renexa  ;  al, 
allantois. 

mother,  this  event  does  not  take  place  without  some  rupture  of 
vessels  and  consequent  haemorrhage. 

It  is  difficult  to  conceive  of  the  great  A^ascularity  of  the 
human  placenta  without  an  actual  examination  of  this  structure 
itself,  which  can  be  done  after  being  cast  off  to  great  advan- 
tage when  floating  in  water ;  by  which  simple  method  also  the 
thinness  and  otlior  cliuracteristics  of  tlic  membranes  can  be 
well  made  out. 

The  great  vessels  conveying  the  fcjetal  ])lood  to  and  from  the 
placenta  are  reduced  to  three,  two  arteries  and  one  vein.  The 
villi  of  the  placenta  (chorion)  an;  usually  .said  to  liang  freely 


gg  ANIMAL   PHYSIOLOGY. 

in  the  blood  of  the  large  irregular  sinuses  of  the  decidua  sero- 
tina;  hut  this  is  so  unlike  what  prevails  in  other  groups  of 
animals  that  we  can  not  refrain  from  helieving  that  the  state- 
ment is  not  wholly  true. 

The  Zonary  Placenta. — In  this  type  the  placenta  is  formed 
along  a  broad  equatorial  belt,  leaving  the  poles  free.  This  form 
of  placentation  is  exemplified  in  the  carnivora,  hyrax,  the  ele- 
phant, etc. 

In  the  dog.  for  example,  the  yelk-sac  is  large,  vascular,  does 
not  fuse  with  the  chorion,  and  persists  throughout.  A  rudiment- 
ary discoid  placenta  is  first  formed,  as  in  the  rabbit ;  this  grad- 
ually spreads  over  the  whole  central  area,  till  only  the  extremes 
(poles)  of  the  o-^^um  remain  free :  villi  appear,  fitting  into  pits 
in  the  uterine  surface,  the  maternal  and  foetal  parts  of  the  pla- 
centa becoming  highly  vascular  and  closely  approximated. 
The  chorionic  zone  remains  wider  than  the  placental.  As  in 
man  there  is  at  birth  a  separation  of  the  maternal  as  well  as 
foetal  part  of  the  placenta— i.  e.,  the  latter  is  deciduate ;  there  is 
also  the  beginning  of  a  decidua  reflexa. 

The  Biffase  Placenta. — As  found  in  the  horse,  pig,  lemur,  etc., 
the  allantois  completely  incloses  the  embryo,  and  it  becomes 
villous  in  all  parts,  except  a  small  area  at  each  pole. 

The  Polycotyledonary  Placenta. — This  form  is  that  met  with  in 
ruminants,  in  which  case  the  allantois  completely  covers  the 
surface  of  the  subzonal  membrane,  the  placental  villi  being 
gathered  into  patches  {cotyledons),  which  are  equivalent  to  so 
many  independent  placentas.  The  component  villi  fit  into  cor- 
responding x^its  in  the  uterine  wall,  which  is  specially  thickened 
at  these  points.  When  examined  in  a  fresh  condition,  under 
water,  they  constitute  very  beautiful  objects. 

Comparing  the  formation,  complete  development,  and  atro- 
phy (in  some  cases)  of  the  various  fcetal  appendages  in  mam- 
mals, one  can  not  but  perceive  a  common  plan  of  structure, 
with  variations  in  the  preponderance  of  one  part  over  another 
here  and  there  throughout.  In  birds  these  structures  are  sim- 
pler, chiefly  because  less  blended  and  because  of  the  presence 
of  much  food-yelk,  albumen,  egg-shell,  etc.,  on  the  one  hand, 
and  the  absence  of  a  uterine  wall,  vrith  which  in  the  mammal 
the  membranes  are  brought  into  close  relationship,  on  the  other ; 
but,  as  will  be  shown  later,  whatever  the  variations,  they  are 
adaptations  to  meet  common  needs  and  subserve  common  ends. 


REPRODUCTION. 


87 


Microscopic  Structure  of  the  Placenta. 

This  varies  somewhat  for  different  forms,  though,  in  that 
there  is  a  supporting  matrix,  minute  (capillary)  blood-vessels, 
and  epithelial  coverings  to  the  foetal  and  maternal  surfaces,  the 
several  forms  agree. 


Fio.  W. 


Fig.  99. 


Fios.  05  to  101.— Dia^ammatic  representation  of  the  minute  .structure  of  the  placenta  (Foster 
and  Balfour,  after  Turner).  F,  festal ;  M,  maternal  placenta  ;  e,  epithelium  of  chorion  ; 
e',  epithelium  of  maternal  placenta ;  rl,  foetal  blood-vessels  ;  d\  maternal  Ijlood-vessels ; 
V.  villus. 

Fio.  y.'j.  -I'lacenta  in  mf>st  generalized  form. 

Fio.  %.  -Structure  of  placenta  of  a  pig. 

Fio.  97.-«>f  a  cow. 

Fio.  'JH.—Or  a  fox. 

Fio.  W,— Of  a  cat. 

Tint  jjig  possesses  the  simplest  form  of  placenta  yet  known. 
The  villi  fit  into  depressions  or  crypts  in  the  maternal  uterine 
mucous  membrane.    The  villi,  consisting  of  a  core  of  connective 


88 


ANIMAL  PHYSIOLOGY. 


tissue,  in  whicli  capillaries  abound,  are  covered  with,  a  flat  epi- 
thelium; the  maternal  crypts  correspond,  being  composed  of 
a  similar  matrix,  lined  with  epithelium  and  permeated  by- 
capillary  vessels,  which  constitute  a  plexus  or  mesh-work.  It 
thus  results  that  two  layers  of  epithelium  intervene  between 
the  maternal  and  f  cetal  capillaries. 

The  arrangement  is  substantially  the  same  in  the  diffuse  and 
the  cotyledonary  placenta. 

In  the  deciduate  placenta,  naturally,  there  is  greater  compli- 
cation. 

In  certain  forms,  as  in  the  fox  and  cat,  the  maternal  tis- 
sue shows  a  system  of  trabeculse  assuming  a  meshed  form, 
in  which  run  dilated  capillaries.  These,  whicli  are  covered 
with  a  somewhat  columnar  epithelium,  are  everywhere  in 
contact  with  the  foetal  villi,  which  are  themselves  covered  with 
a  flat  epithelium. 


6.  F, 


Fig.  100.  Fig.  101. 

Fig  100.— Placenta  of  a  sloth.  Flat  maternal  epithelial  cells  shown  in  position  on  right  side  ; 
on  left  they  are  removed  and  dilated  ;  maternal  vessel  with  its  blood-corpuscles  exposed. 

Fig.  101.— structure  of  human  placenta  ;  ds,  decidua  serotina  ;  t,  trabeculae  of  serotina  passing 
to  foetal  villi ;  ca,  curling  artery  ;  up,  utero-placental  vein  ;  .r,  prolongation  of  maternal 
tissue  on  exterior  of  villus,  outside  cellular  layer  e'.  which  may  represent  either  endothe- 
lium of  maternal  blood-vessels  or  delicate  connective  tissue  of  the  serotina  or  both  ;  e'  ma- 
ternal cells  of  the  serotina. 

In  the  case  of  the  sloth,  with  a  more  discoidal  placenta,  the 
dilatation  of  capillaries  and  the  modification  of  epithelium 
are  greater. 

In  the  placenta  of  the  apes  and  of  the  human  subject  the 
most  marked  departure  from  simplicity  is  found.    The  maternal 


REPRODUCTION.  89 

vessels  are  said  to  constitute  large  intercommunicating  sinuses ; 
the  villi  may  hang  freely  suspended  in  these  sinuses,  or  be 
anchored  to  their  walls  by  strands  of  tissue.  There  is  believed 
to  be  only  one  layer  of  epithelial  cells  between  the  vessels  of 
mother  and  foetus  in  the  later  stages  of  pregnancy.  This, 
while  closely  investing  the  foetal  vessels  (capillaries),  really 
belongs  to  the  maternal  structures.  The  significance  of  this 
general  arrangement  will  be  explained  in  the  chapter  on  the 
physiological  aspects  of  the  subject. 

It  remains  to  inquire  into  the  relation  of  these  forms  to  one 
another  from  a  x>l^ylogenetic  (derivative)  point  of  view,  or  to 
trace  the  evolution  of  the  placenta. 

Evolution. — Passing  by  the  lowest  mammals,  in  which  the 
placental  relations  are  as  yet  imperfectly  understood,  it  seems 
clear  that  the  simplest  condition  is  found  in  the  rodentia. 
Thus,  in  the  rabbit,  as  has  been  described,  both  yelk-sac  and 
allantois  take  a  nutritive  part ; '  but  the  latter  remains  small. 
In  forms  above  the  rodents,  the  allantois  assumes  more  and 
more  importance,  becomes  larger,  and  sooner  or  later  predomi- 
nates over  the  yelk-sac. 

The  discoidal,  zonary,  cotyledonary,  etc.,  are  plainly  evolu- 
tions from  the  diffuse,  for  both  differentiation  of  structure  and 
integration  of  parts  are  evident.  The  human  placenta  seems 
to  have  arisen  from  the  diffuse  form;  and  it  Avill  be  remem- 
bered that  it  is  at  one  period  represented  by  the  chorion  with 
its  villi  distributed  universally. 

The  resemblance  in  the  embryonic  membranes  at  any  early 
stage  in  man  and  other  mammals  to  those  of  birds  certainly 
suggests  an  evolution  of  some  kind,  though  exactly  along  what 
lines  that  has  taken  place  it  is  difficult  to  determine  with  exact- 
ness ;  however,  as  before  remarked,  nearly  all  the  complications 
of  the  higher  forms  arise  by  concentration  and  fusion,  on  the  one 
hand,  and  atrophy  and  disappearance  of  parts  once  functionally 
active,  on  the  other. 

Summary. — The  ovum  is  a  typical  cell ;  unspecialized  in  most 
directions,  but  so  specialized  as  to  evolve  from  itself  compli- 
cated structures  of  higher  character.  The  segmentation  of  the 
ovum  is  usually  preceded  by  fertilization,  or  the  union  of  the 
nuclei  of  male  and  female  cells,  which  is  again  preceded  by  the 
extrusion  of  polar  globules.  In  the  early  changes  of  the  ovum, 
including  segmentation,  periods  of  rest  and  activity  alternate. 
The  method  of  segmentation  has  relation  to  the  quantity  and 
arrangement  of  the  food-yelk.     Ova  are  divisible  generally 


90  ANIMAL  PHYSIOLOGY. 

into  completely  segmenting  (holoblastic),  and  those  that  under- 
go segmentation  of  only  a  part  of  their  substance  (meroblastic) ; 
but  the  processes  are  fundamentally  the  same. 

Provision  is  made  for  the  nutrition,  etc.,  of  the  ovum,  when 
fertilized  (oosperm)  by  the  formation  of  yelk-sac  and  allan- 
tois;  as  development  proceeds,  one  becomes  more  prominent 
than  the  other.  The  allantois  may  fuse  with  adjacent  mem- 
branes and  form  at  one  part  a  condensed  and  hypertrophied 
chorion  (placenta),  with  corresponding  atrophy  elsewhere.  The 
arrangement  of  the  placenta  varies  in  different  groups  of  ani- 
mals so  constantly  as  to  furnish  a  basis  for  classification.  What- 
ever the  variations  in  the  structure  of  the  placenta,  it  is  always 
highly  vascular ;  its  parts  consist  of  villi  fitting  into  crypts  in 
the  maternal  uterine  membrane — both  the  villi  and  the  crypts 
being  provided  with  capillaries  supported  by  a  connective-tissue 
matrix  covered  externally  by  epithelium.  The  placenta  in  its 
different  forms  would  appear  to  have  been  evolved  from  the 
diffuse  type. 

The  peculiarities  of  the  embryonic  membranes  in  birds  are 
owing  to  the  presence  of  a  large  food-yelk,  egg-shell,  and  egg- 
membranes  ;  but  throughout,  vertebrates  follow  in  a  common 
line  of  development,  the  differences  which  separate  them  into 
smaller  and  smaller  groups  appearing  later  and  later.  The 
same  may  be  said  of  the  animal  kingdom  as  a  whole.  This 
seems  to  point  clearly  to  a  common  origin  with  gradual  diver- 
gence of  type. 


THE   DEVELOPMENT   OF   THE   EMBRYO   ITSELF. 

We  now  turn  to  the  development  of  the  body  of  the  animal 
for  which  the  structures  we  have  been  describing  exist.  It  is 
important,  however,  to  remember  that  the  development  of  parts, 
though  treated  separately  for  the  sake  of  convenience,  really 
goes  on  together  to  a  certain  extent ;  that  new  structures  do  not 
appear  suddenly  but  gradually  ;  and  that  the  same  law  apj^lies 
to  the  disappearance  of  organs  which  are  being  superseded  by 
others.  To  represent  this  completely  would  require  lengthy  de- 
scriptions and  an  unlimited  number  of  cuts  ;  but  with  the  above 
caution  it  is  hoped  the  student  may  be  able  to  avoid  erroneous 
conceptions,  and  form  in  his  own  mind  that  series  of  pictures 
which  can  not  be  well  furnished  in  at  least  the  space  we  have 
to  devote  to  the  subject.     But,  better  than  any  abstract  state- 


THE  DEVELOPMENT   OP  THE  EMBRYO  ITSELF. 


91 


ments  or  pictorial  representations,  would  be  tlie  examination  of 
a  setting  of  eggs  day  by  day  during  their  development  under  a 


Fio.  102.— Various  stages  in  the  development  of  the  frog  from  the  egg  (after  Howes).  1.  The 
segmenting  ovum,  showing  first  cleavage  furrow.  2.  Section  of  the  above  at  rig:ht  angles 
to  the  furrow.  3.  Same,  on  appearance  of  second  furrow,  viewed  .slitjlitly  from  above. 
4.  The  latter  seen  from  beneath,  ."j.  The  same,  on  appearance  of  first  horizontal  furrow. 
6.  The  saniH.  seen  from  above.  7.  Longitudinal  section  of  0.  8  mid  ti.  Two  jiliascs  In 
segmentation,  on  appearance  of  fourth  and  fifth  furrows.  10.  Longitudinal  vertical  sct'tion 
at  a  slightly  later  stajje  than  the  above.  11.  Later  stape.  Ui)i)fr  ])iKmciitc(l  pole  iliviiling 
more  rapidlj- than  lower.  12.  Later  phase  of  II.  18.  fjoiigifuilinal  vertical  section  of  12. 
14.  Segmenting  ovum  at  bla.stopore  stajje.  1.5.  LonKitudinal  vertical  section  of  same. 
13  and  1.5  x  V)  lall  others  x  5).  Ki.  Longitudinal  vertical  section  of  embryo  at  a  stage 
later  than  14  (1  x  10).  71c,  nucleus;  c.  c.  cleavage  cavity  ;  »-;>,  ejjiblast ;  /.  t,  yelk-bearing 
lower-layer  celts  ;  01,  blastopore  :  a/,  archenteron  (mid-gut)  ;  hh,  hyijoblast ;  mn,  undiffer- 
entiated niesoblast ;  ch,  notf>chord  ;  11.  a,  neural  (cerebro-spinal)  axis. 


ben.  This  is  a  very  simple  matter,  and,  while  the  making  and 
mounting  of  sections  from  hardened  specimens  is  valuable,  it 
may  require  more  time  than  the  student  can  spare ;  but  it  is 
neitlier  so  valuable  nor  so  easily  accomplislied  as  wliat  we  have 
indicated  ;  for,  while  the  lack  of  sections  made  by  the  student 


92  ANIMAL   PHYSIOLOGY. 

may  be  made  up  in  part  by  the  exMbition  to  liim  of  a  set  of 
specimens  permanently  mounted  or  even  by  plates,  nothing  can, 
in  our  opinion,  take  the  place  of  the  examination  of  eggs  as  we 
have  suggested.  It  prepares  for  the  study  of  the  development 
of  the  mammal,  and  exhibits  the  membranes  in  a  simplicity, 
freshness,  and  beauty  which  impart  a  knowledge  that  only 
such  direct  contact  with  nature  can  supply.  To  proceed  with 
great  simplicity  and  very  little  apparatus,  one  requires  but  a 
forceps,  a  glass  dish  or  two,  a  couple  of  watch-glasses,  or  a 
broad  section-lifter  (even  a  case-knife  will  answer),  some  water, 
containing  just  enough  salt  to  be  tasted,  rendered  lukewarm 
(blood-heat). 

Holding  the  egg  longitudinally,  crack  it  across  the  center 
transversely,  gently  and  carefully  pick  away  the  shell  and  its 
membranes,  when  the  blastoderm  may  be  seen  floating  upward, 
as  it  always  does.  It  should  be  well  examined  in  position, 
using  a  hand  lens,  though  this  is  not  essential  to  getting  a  fair 
knowledge;  in  fact,  if  the  examination  goes  no  further. than 
the  naked-eye  appearances  of  a  dozen  eggs,  selecting  one  every 
twenty-four  hours  during  incubation,  when  opened  and  the 
shell  and  membranes  well  cleared  away,  such  a  knowledge  will 
be  supplied  as  can  be  obtained  from  no  books  or  lectures  how- 
ever good.  It  will  be,  of  course,  understood  that  the  student 
approaches  these  examinations  with  some  ideas  gained  from 
plates  and  previous  reading.  The  latter  will  furnish  a  sort  of 
biological  pabulum  on  which  he  may  feed  till  he  can  furnish 
for  himself  a  more  natural  and  therefore  more  healthful  one. 
While  these  remarks  apply  with  a  certain  degree  of  force  to  all 
the  departments  of  physiology,  they  are  of  special  importance 
to  aid  the  constructive  faculty  in  building  up  correct  notions 
of  the  successive  rapid  transformations  that  occur  in  the  de- 
velopment of  a  bird  or  mammal. 

Fig.  103  shows  the  embryo  of  the  bird  at  a  very  early 
period,  when  already,  however,  some  of  the  main  outlines  of 
structure  are  marked  out.  Development  in  the  fowl  is  so  rapid 
that  a  few  days  suffice  to  outline  all  the  principal  organs  of 
the  body.  In  the  mammal  the  process  is  slower,  but  in  the 
main  takes  place  in  the  same  fashion. 

As  the  result  of  long  and  patient  observation,  it  is  now  set- 
tled that  all  the  parts  of  the  most  complicated  organism  arise 
from  the  three-layered  blastoderm  previously  figured ;  every 
part  may  be  traced  back  as  arising  in  one  or  other  of  these  lay- 
ers of  cells — the  epiblast,  mesoblast,  or  hypoblast.    It  frequently 


THE   DEVELOPMENT   OP   THE   EMBRYO   ITSELF. 


93 


aT/z 


happens  that  an  organ  is  made  up  of  cells  derived  from  more 
than  one  layer.  Structures  may,  accordingly,  be  classified  as 
epiblastic,  mesoblastic,  or  hypoblas- 
tic ;  for,  when  two  strata  of  cells 
unite  in  the  formation  of  any  part, 
one  is  always  of  subordinate  impor- 
tance to  the  other :  thus  the  digestive 
organs  are  made  up  of  mesoblast  as 
well  as  hypoblast,  but  the  latter 
constitutes  the  essential  secreting 
cell  mechanism.  As  already  indi- 
cated, the  embryonic  membranes 
are  also  derived  from  the  same 
source. 

The  epihlast  gives  rise  to  the  skin 
and  its  appendages  (hair,  nails,  feath- 
ers, etc.),  the  whole  of  the  nervous 
system,  and  the  chief  parts  of  the  or- 
gans of  special  sense. 

The  mesoblast  originates  the  skel- 
eton, all  forms  of  connective  tissue, 
including  the  framework  of  glands, 
the  muscles,  and  the  epithelial  (en- 
dothelial) structures  covering  serous 
membranes. 

The  hypoblast  furnishes  the  se- 
creting cells  of  the  digestive  tract 
and  its  appendages — as  the  liver  and 
pancreas — the  lining  epithelium  of 
the  lungs,  and  the  cells  of  the  secret- 
ing mucfjus  membranes  of  their 
framework  of  bronchial  tubes. 

It  is  difficult  to  overrate  the  im- 
portance of  these  morphological  gen- 
eralizations for  the  physiologist ;  for, 
once  the  origin  of  an  organ  is  known, 
its  functi(m  and  physiological  rela- 
tions generally  may  be  predicted  with 
considerable  certainty.  We  shall  en- 
deavor to  make  this  prominent  in  the  futlire  chapters  of 
work. 

Being  prepared  with  these  generalizations,  we  continue  our 
study  of  the  develoxjment  of  the  bird's  embryo,    Befon;  tlie  end 


Fig.  103.— Embryo  fowl  3  mm.  long, 
of  about  twenty -four  hours,  seen 
from  <al)ove..  1  x  39.  (Haddon, 
after  KoUiker.)  A/(i,  union  of 
the  medullary  folds  in  the  region 
of  the  hind-brain  ;  Pr.  primitive 
streak  ;  Pz,  parietal  zone  ;  Rf, 
posterior  portion  of  widely-open 
neural  groove  ;  Rf,  anterior  part 
of  neural  groove  ;  Kw,  neural 
ridge  ;  Stz,  trunk-zone  :  vAf,  an- 
terior amniotic  fold  ;  v/>,  anterior 
umbilical  sinus  showing  through 
the  blastoderm.  His  divides  the 
embryonic  rudiment  into  a  cen- 
tral trunk-zone,  and  a  pair  of 
lateral  or  parietal  zones. 

this 


94 


ANIMAL  PHYSIOLOGY. 


of  the  first  twenty-four  hours  such,  an  appearance  as  that  repre- 
sented in  Fig.  104  is  presented. 


Fig.  104.— Transverse  section  through  the  medullary  groove  and  half  the  blastoderm  of  a 
chick  of  eighteen  hours  (Foster  and  Balfour).  E,  epiblast ;  M,  mesoblast ;  H,  hypoblast ; 
ni/,  medullary  fold  ;  mg.  medullary  groove  ;  c/i,  notochord. 


The  mounds  of  cells  forming  the  medullary  folds  are  seen 
coming  in  contact  to  form  the  medullary  {neural)  canal. 


Fig.  105.— Transverse  section  of  embryo  chick  at  end  of  first  day  (after  Kolliker).  M,  meso- 
blast ;  H,  hjrpoblast ;  ni,  medullary  plate  ;  E,  epiblast :  nigr,  medullary  groove  ;  nif,  me- 
dullary told  ;  c/i,  chorda  dorsalis  ;  P,  protovertebral  plate  ;  dm,  division  of  mesoblast. 

The  notochord,  marking  out  the  future  bony  axis  of  the 
body,  may  also  be  seen  during  the  first  day  as  a  well-marked 
linear  extension,  just  beneath  the  medullary  groove.     The  cleav- 


Fig.  106.— Transverse  section  of  chick  at  end  of  second  day  (Kolliker).  E,  epiblast :  H.  hypo- 
blast ;  e.  m,  external  plate  of  mesoblast  dividing  (cleavage  of  mesoblast)  ;  ?n./,  medullary 
fold  ;  m.  g,  medullary  groove  ;  ao,  aorta  ;  p,  pleuroperitoneal  cavity  ;  P,  protovertebral 
plate. 

age  of  the  mesoblast,  resulting  in  the  commencement  of  the 
formation  of  somatojjleure  (body-fold)  and  the  splanchnopleure 
(visceral  fold),  is  als(3  an  early  and  important  event.  These  give 
rise  between  them  to  the  pleuro-peritoneal  cavity.  The  portions 
of  mesoblast  nearest  the  neural  canal  form  masses  {vertebral 
plates)  distinct  from  the    thinner   outer    ones    {lateral  plates). 


THE  DEVELOPMENT   OF  THE  ExMBRYO   ITSELF. 


95 


op.v. 


m.b 


The  vertebral  plates,  wlien  distinctly  marked  off,  as  repre- 
sented in  the  figure,  are  termed  the  protovertehrce  (mesohlast ic 
somites),  and  represent  the  future  vertebrae  and  the  voluntary- 
muscles  of  the  trunk ;  the  former  arising  from  the  inner  sub- 
divisions, and  the  latter  from 
the  outer  {inusde-iilates).  It 
will  be  understood  that  the  pro- 
tovertebrae  are  the  results  of 
transverse  division  of  the  col- 
umns of  mesoblast  that  formed 
the  vertebral  plates. 

Before  the  permanent  verte- 
brae are  formed,  a  reunion  of 
the  original  protovertebrae  takes 
place  as  one  cartilaginous  pillar, 
followed  by  a  new  segmentation 
midway  between  the  original 
divisions. 

It  thus  appears  that  a  large 
number  of  structures  either  ap- 
pear or  are  clearly  outlined  dur- 
ing the  first  day  of  incubation : 
the  primitive  streak,  primitive 
groove,  medullary  plates  and 
groove,  the  neural  canal,  the 
head-fold,  the  cleavage  of  the 
mesoblast,  the  protovertebrae, 
with  traces  of  the  amnion  and 
area  opaca. 

During  the  second  day  near- 
ly all  the  remaining  important 
structures  of  the  chick  are 
marked  out,  while  those   that 

arose  during  the  first  day  have  progressed.  Thus,  the  medullary 
folds  close ;  there  is  an  increase  in  the  number  of  protoverte- 
brae ;  the  formation  of  a  tubular  heart  and  the  great  blood-ves- 
sels ;  the  appearance  of  the  Wolffian  duct ;  the  progress  of  the 
head  region  ;  the  appearance  of  the  three  cerebral  vesicles  at 
the  anterior  extremity  of  the  neural  canal ;  the  subdivision  of 
the  first  cerebral  vesicle  into  the  optic  vesicles  and  the  begin- 
nings of  the  cerebrum ;  the  auditory  pit  arising  in  the  third 
cerebral  vesicle  (hind-brain);  cranial  flexure  commences;  both 
liead  and  tail  folds  become  more  distinct;  the  heart  is  not  only 


Fig.  107.— Embryo  of  chick,  between  thirty 
and  thirtj'-six  hours,  viewed  from  above 
as  an  opaque  object  (Foster  and  Balfour). 
/.  6,  forebrain  ;  m.  6,  midbrain  ;  h.  b, 
hind-brain;  op.  v,  optic  vesicle;  au. p, 
auditory  pit ;  o.  /,  vitelline  vein  ;  p.  v, 
niesoblastic  somite  :  m.  f.  li^^'  of  func- 
tion of  medullary  fnlilsalidvc  medullarv 
canal;  s.  r,  sinus  rh<:iml)c>i<lalis  :  ^  tail- 
fold  ;  p.r,  remains  of  primitive  groove  ; 
a.  p,  area  pellucida. 


ANIMAL  PHYSIOLOGY. 


formed,  but  its  curvature  becomes  more  marked  and  rudiments 
of  auricles  arise ;  while  outside  the  embryo  itself  the  circula- 
tion of  the  yelk-sac  is  established,  the  allautois  originates,  and 
the  amnion  makes  rapid  progress. 

It  may  be  noticed  that  the  cerebral  vesicles,  the  optic  vesi- 
cles, and  the  auditory  pit  are  all  derived  from  the  epiblastic 
accumulations  which  occur  in  the  anterior  extremity  of  the 
embryo ;  and  their  early  appearance  is  prophetic  of  their  physi- 
ological importance. 

The  heart,  too,  so  essential  for  the  nutrition  of  the  embryo, 
by  distributing  a  constant  blood-stream,  is  early  formed,  and 


Fig.  108. — Diagram  representing  under  surface  of  an  embryo  rabbit  of  nine  day.s  and  three 
hours  old,  illustrating  development  of  the  heart  (after  Allen  Thomson).  A,  view  of  the 
entire  embryo  ;  B,  an  enlarged  outline  of  the  heart  of  A  ;  C,  later  stage  of  the  development 
of  B  ;  h  h,  ununited  heart ;  a  a,  aortas  ;  vv,  vitelline  veins. 

becomes  functionally  active.  It  arises  beneath  the  hind-end  of 
the  fore-gut,  at  the  point  of  divergence  of  the  folds  of  the 
splanchnopleure,  and  so  lies  within  the  pleuro-peritoneal  cav- 
ity, and  is  derived  from  the  mesoblast.  At  the  beginning  the 
heart  consists  of  two  solid  columns  ununited  in  front  at  first ; 
later,  these  fuse,  in  part,  so  that  they  have  been  compared  with 
an  inverted  Y,  in  which  the  heart  itself  would  correspond  to  the 
lower  stem  of  the  letter  (a)  and  the  great  veins  (vitelline)  to  its 
main  limbs.  The  solid  cords  of  mesoblast  become  hollow  prior 
to  their  coalescence,  when  the  two  tubes  become  one. 


THE  DEVELOPMENT  OF  THE  EMBRYO  ITSELF. 


97 


Tlie  entire  blood- vascular  system  originates  in  the  mesoblast 
of  the  area  opaca  especially ;  at  first  appearing  in  isolated  spots 
which  come  together  as  actual  vessels  are  formed.  The  student 
who  will  pursue  the  plan  of  examining  a  series  of  incubating 
eggs  will  be  struck  with  the  early  rise  and  rauid  progress  of  the 


Fig.  109.— Cbick  on  third  day,  seen  from  beneath  as  a  transparent  object,  the  head  being 
turned  to  one  side  (Foster  and  Balfour),  a',  false  amnion  ;  a,  amnion  ;  CH,  cerebral 
hemisphere  ;  Fli,  M/i,  JIB,  anterior,  middle,  and  posterior  cerebral  vesicles  ;  OP,  optic 
vesicle  ;  ot,  auditory  v('si<-le  ;  ofv,  oniphalo-mesenteric  veins  ;  Ht,  heart ;  Ao,  bulbus  arte- 
riosus ;  ch.  notochord  ;  O/a,  omphalo-mesenteric  arteries  ;  Pv,  protovertebraj ;  x,  point  of 
divergence  of  the  splanchnopleural  folds  ;  y,  termination  of  the  foregut,  v. 

vascular  system  of  the  embryo,  which  takes,  when  complete, 
-uch  a  form  as  is  represented  diagramatically  in  Fig.  113. 

The  blood  and  the  blood-vessels  arise  simultaneously  from 
the  cells  of  the  mesoblast  by  outgrowths  of  nuclear  prolifera- 
tion, and  in  the  case  of  vessels  (Fig.  147)  extension  of  processes, 
fusion,  and  excavation. 

The  fore-gut  is  formed  by  the  unitjn  of  the  folds  of  the 
planchnopleure  from  before  backward,  and  the  hind-gut  in  a 
imilar  manner  by  fusion  from  behind  forward. 
7 


98 


ANIMAL  PHYSIOLOGY. 


The  excretory  system  is  also  foreshadowed  at  an  early  pe- 
riod by  the  Wolffian  duct  (Fig.  114),  a  mass  of  mesoblast  cells 
near  which  the  cleavage  of  the  mesoblast  takes  place. 


Fig  110  —Diagram  of  the  heart  and  principal  arteries  of  the  chick  (Quam).  A  represents  an 
earlier,  and  B  and  C  later  stages.  1, 1,  omphalo-mesenteric  veins ;  2,  auricle;  3  ventricle; 
4,  aortic  bulb  ;  5,  5,  primitive  aortee  ;  6,  6,  omphalo-mesenteric  arteries  ;  A,  united  aortse. 

During  the  latter  part  of  the  second  day  the  vascular  system, 
including  the  heart,  makes  great  progress.     The  latter,  in  con- 


FiG.  111.— Diagrammatic  outlines  of  the  early  arterial  system  of  the  mammal  vertebrate  em- 
bryo (aftef  Allen  Thomson).  A.  At  a  period  corresponding  to  the  thu-ty-sixth  or  thirty- 
eighth  hour  of  incubation.  B.  Later  stage,  with  two.  pairs  of  aortic  arches,  h,  bulbus 
arteriosus  of  heart ;  v,  vitelUne  arteries  ;  1-5,  the  aortic  arches.  The  dotted  lines  indicate 
the  position  of  the  future  arches. 

sequence  of  excessive  growth  and  the  alteration  of  the  relative 
position  of  other  parts,  becomes  bent  up  on  itself,  so  that  it 


THE  DEVELOPMENT   OF  THE  EMBRYO  ITSELF. 


99 


presents  a  curve  to  the  right  which  represents  the  venous  part 
and  one  to  the  left,  answering  to  the  arterial.  The  rudiments 
of  the  auricles  also  are  to  be  seen. 

The  arterial  system  is  represented  at  this  stage  by  the  ex- 
panded portion  of  the  heart  known  as  the  hulhus  arteriosus, 
and  two  extensions  from  it,  the  aortse, 
which  uniting  above  the  alimentary 
canal,  form  a  single  posterior  or  dorsal 
aorta.  From  these  great  arterial  ves- 
sels the  lesser  ones  arise,  and  by  sub- 
division constitute  that  great  mesh- 
work  represented  diagrammatically  in 
Figs.  112, 11 3,  from  which  the  course  of 
the  circulation  may  be  gathered.  The 
beating  of  the  heart  commences  be- 
fore the  corpuscles  have  become  nu- 
merous, and  while  the  tubular  system, 
through  which  the  blood  is  to  be 
driven,  is  still  very  incomplete. 

The  events  of  the  third  day  are  of 
the  nature  of  the  extension  of  parts 
already  marked  out  rather  than  the 
formation  of  entirely  new  ones.  The 
following  are  the  principal  changes : 
The  bending  of  the  head-end  down- 
ward (cranial  flexure) ;  the  turning  of 
the  embryo  so  that  it  lies  on  its  left 
side ;  the  completion  of  the  vitelline 
circulation ;  the  increase  in  the  curva- 
ture of  the  heart  and  its  complexity 
of  structure  by  divisions  ;  the  appear- 
ance of  additional  aortic  arches  and 
of  the  cardinal  veins ;  the  formation 
of  four  visceral  clefts  and  five  vis- 
ceral arches ;  a  series  of  progressive 
changes  in  the  organs  of  the  special 
senses,  such  as  the  formation  of  the 
lens  of  the  eye  and  a  secondary  optic 
vesicle;  the  closing  in  of  the  optic 
vesicle ;  and  the  formation  of  the  na- 
sal pits.  In  the  region  of  the  future  brain,  the  vesicles  of  the 
cerebral  hemispheres  become  distinct ;  the  hind-brain  sejjarates 
into  cerebellum  and  medulla  oblongata;  the  nerves,  both  cra- 


FiG.  112.— Diagram  of  the  embry- 
onic vascular  system  (Wieder- 
sheim).  a.  atrium  ;  A.  A,  dor- 
sal aorta  ;  Ab,  branchial  ves- 
sels ;  Arxl,  caudal  artery  ;  All, 
allantoic  (hypogastric)  arter- 
ies ;  Am,  vi6?lline  arteries  ;  B. 
bulbus  arteriosus  ;  c.  c'  exter- 
nal and  internal  carotids  ;  /), 
ductus  Cuvieri  ( precaval  veins) ; 
E,  external  iliac  arteries  ;  H.  C, 
posterior  cardinal  vein  ;  /c, 
common  iliac  arteries  ;  K.  L, 
Kill  clefts  ;  H.A,  right  and  left 
roots  of  the  aorta  ;  .S'.  S', 
branchial  collecting  trunks  or 
veins  ;  Sh,  subclavian  artery  ; 
Sh',  subclavian  vein  ;  Si.  sinus 
venosus  ;  V,  ventricle  ;  VC,  an- 
terior cardinal  vein  ;  I'm,  vitel- 
line veins. 


100 


ANIMAL  PHYSIOLOGY. 


nial  and  spinal,  bud  out  from  the  nervous  centers.  The  ali- 
mentary canal  enlarges,  a  fore-gut  and  hind-gut  being  formed, 
the  former  being  divided  into  oesophagus,  stomach,  and  duode- 


AA. 


Fig.  113.— Diagram  of  circulation  of  yelk-sac  at  end  of  third  day  (Foster  and  Balfour)  > 
Blastoderm  seen  from  below.  Arteries  made  black.  H,  heart ;  AA,  second,  third,  and 
fourth  aortic  arches  ;  AO,  dorsal  aorta  ;  L.  Of.  A,  left  vitelline  artery ;  B.  Of.  A^  right 
vitelline  artery  ;  S.  T,  sinus  terminalis  ;  L.  Of,  left  vitelline  vein  ;  R.  Of,  right  vitelline 
vein  ;  S.  V,  sinus  venosus  ;  D.  C,  ductus  Cuvieri ;  S.  Ca.  V,  superior  cardinal  or  jugular 
vein  ;  V.  Ca,  inferior  cardinal  vein. 


num ;  the  latter  into  the  large  intestine  and  the  cloaca.  The 
lungs  arise  from  the  alimentary  canal  in  front  of  the  stomach ; 
from  similar  diverticula  from  the  duodenum,  the  liver  and 
pancreas  originate.  Changes  in  the  protovertebrse  and  muscle- 
plates  continue,  while  the  WolfELan  bodies  are  formed  and  the 
Wolffian  duct  modified. 

Up  to  the  third  day  the  embryo  lies  mouth  downward,  but 
now  it  comes  to  lie  on  its  left  side.  See  Fig.  109  with  the  ac- 
companying description,  it  being  borne  in  mind  that  the  view  is 
from  below,  so  that  the  right  in  the  cut  is  the  left  in  the  em- 


THE  DEVELOPMENT   OF  THE  EMBRYO   ITSELF. 


101 


Fig.  116. 


i-iu,  11:). 


Fio.  114.  -Transverse  section  through  lumbar  region  of  an  embryo  at  end  of  fourth  day  (Fos- 
ter an«l  Balfour),  nc.  neural  canal :  pr.  postf  rinr  root  of  spinal  nerve  with  ganglion  ; 
fir.  anterior  ro<>t ;  A.  G.  C.  anterior  gray  I'nluinn  of  siiinal  curd  :  A.  It'.  C,  anterior  white 
column  in  course  of  formation  :  m.  p.  nnisi-li-  plate  :  rh.  nutocliord  ;  It'.  /?,  Wdllliim  ridge  ; 
A(J.  dorsal  aorta  ;  r.  r.  u.  post^-rior  cardinal  vein  ;  II'.  d,  WultYlan  duct  :  IT.  /;.  Wolffian 
IxxJy,  consisting  of  tubules  and  Malpighian  corpuscles  ;  g.  e.  germinal  epithelium  ;  d,  ali- 
mentary eanal  ;  .U.  eorniiiein-jng  mesentery  :  .SO,  .soniatopleure  ;  SP,  splanchnopleure  ; 
V.  bI<K>d-ves.s<ds  :  pfi.  (deuroperitoneal  cavity. 

Fio.  ll.'j.  — diagram  of  portion  of  digestive  tract  of  chick  on  fourth  day  (after  Oiitte).  The 
black  line  repre«<'nts  hypoblast ;  the  shaderl  portion,  mesotilast  :  li/.  lung  diverticulum, 
exi)anding  at  bases  into  primary  lung  vesicle  ;  nt,  stomai-h  :  /.  liver  ;  />,  pancreas. 

Fio.  11»).  — Head  of  cliiek  of  third  day.  viewed  sidewise  as  a  transparent  iibject  iHu.vley*.  la, 
cerebral  heininjiheres  ;  Ih,  vesicle  of  third  ventricle:  II,  imd-brain  :  III,  hind-brain;  a, 
optic  vesicle  ;  7,  na.sal  pit :  h.  otic  vesicle  ;  d,  iiifundiiiulurn  ;  p,  pineal  body  ;  h,  notochord; 
V,  fifth  nerve:  VII,  H»fventh  nerve;  VIII,  united  glossopharyngeal  and  i>neumoga8tric 
nerves.    1,  2,  3,  4,  5,  the  five  visceral  folds. 


102 


ANIMAL  PHYSIOLOGY. 


bryo  itself.  Fig.  114  gives  appearances  furnislied  by  a  vertical 
transverse  section.  The  relations  of  the  parts  of  the  digestive 
tract  and  the  mode  of  origin  of  the  lungs  may  be  learned  from 
Fig.  115. 


Vir  117  — TTpad  of  chick  of  fourth  day,  viewed  from  below  as  an  opaque  object  (Foster  and 
Balfour)  The  neck  is  cut  across  between  third  and  fourth  visceral  folds.  C.  H,  cerebral 
hem°spl^eres  i^  S,  vesicle  of  third  ventricle  :  Op.  eyeball ;  nf,  naso-frontal  process  ;m, 
civity  of  moAth  ;  S.  m,  superior  maxillary  process  of  F.  1,  the  first  visceral  fold  (mandibu- 
lar arch) ;  F.  2,  F.  3,  second  and  third  visceral  arches  ;  N,  nasal  pit. 

An  examination  of  the  figures  and  subjoined  descriptions 
must  suffice  to  convey  a  general  notion  of  the  subsequent  prog- 


G.Ph. 


VII. 


MP. 


Vxa  118  —Embryo  at  end  of  fourth  day,  seen  as  a  transparent  object  (Foster  and  Balfour). 
Off  cere^raThemilphere;  F.  B.,  for?4)rain,  or  vesicle  of  third  ^^ntoc  e  tbalamencepha- 
lon)  with  pineal  gland  (Pii)  projecting  :  31.  B,  mid-bram  ;  Cb  cerebellum  ;  II .  P,  fourtn 
ventricle-  i  lent-  chs\  choroid  slit  f  Cen.  V.  auditory  vesicle;  sm  superior  maxillary 
Drocess  •  IF '3^"ltc,  first,  second,  etc.,  visceral  folds  ;  F,  fifth  nerve;  VII  seventh  nerve; 
&  pl!  glossopharyngeal  ierve  ;  Pj,,  pneumogastric.  The  distribution  of  these  nerves  is 
also  iAchcated  :  ch.  notochord  ;  Ht,  heart ;  MP.  muscle-plates  ;  W  wmg  ;  H.  i;.  ^'"id-limb. 
The  amnion  has  been  removed.    Al,  allantois  protruding  from  cut  end  ot  somatic  stalk  &S. 


DEVELOPMENT  OF  THE  VASCULAR  SYSTEM.      103 

ress  of  tlie  embryo.  Special  points  will  be  considered,  either  in 
a  separate  chapter  now,  or  deferred  for  treatment  in  the  body 
of  the  work  from  time  to  time,  as  they  seem  to  throw  light 
upon  the  subjects  under  discussion. 


DEVELOPMENT    OF    THE    VASCULAR   SYSTEM    IN   VERTE- 
BRATES. 

This  subject  has  been  incidentally  considered,  but  it  is  of 
such  importance  morphological,  physiological,  and  pathological, 
as  to  deserve  special  treatment. 

In  the  earliest  stages  of  the  circulation  of  a  vertebrate  the 
arterial  system  is  made  up  of  a  pair  of  arteries  derived  from  the 
single  hidbus  arteriosus  of  the  heart,  which,  after  passing  for- 
ward, bends  round  to  the  dorsal  side  of  the  pharynx,  each  giving 
off  at  right  angles  to  the  yelk-sac  a  vitelline  artery ;  the  aortse 
unite  dorsally,  then  again  separate  and  become  lost  in  the  pos- 
terior end  of  the  embryo.  The  so-called  arches  of  the  aorta 
are  large  branches  in  the  anterior  end  of  the  embryo  derived 
from  the  aorta  itself. 

The  venous  system  corresponding  to  the  above  is  composed 
of  anterior  and  posterior  pairs  of  longitudinal  (cardinal)  veins, 
the  former  (jugular,  cardinal)  uniting  with  the  posterior  to 
form  a  common  trunk  {ductus  Cuvieri)  by  which  the  venous 
blood  is  returned  to  the  heart.  The  blood  from  the  posterior 
part  of  the  yelk-sac  is  collected  by  the  vitelline  veins,  which 
terminate  in  the  median  sinus  venosus. 

The  Later  Stages  of  the  Foetal  Circulation. — Corresponding  to 
the  number  of  visceral  arches  five  pairs  of  aortic  arches  arise ; 
but  they  do  not  exist  together,  the  first  two  having  undergone 
more  or  less  complete  atrophy  before  the  others  appear.  Figs. 
119,  120  convey  an  idea  of  how  the  permanent  forms  (indicated 
by  darker  shading)  stand  related  to  the  entire  system  of  vessels 
in  different  groups  of  animals.  Thus,  in  birds  the  right  (fourth) 
aortic  arch  only  remains  in  connection  with  the  aorta,  the  left 
forming  tlie  subclavian  artery,  while  the  reverse  occurs  in  mam- 
mals.    The  fifth  arch  (pulmonary)  always  supplies  the  lungs. 

The  arrangement  of  the  principal  vessels  in  the  bird,  mam- 
mal, etc.,  is  represented  on  jjage  104.  In  mammals  the  two 
primitive  anterior  abdominal  {allantoic)  veins  develoi)  early 
and  unite  in  front  with  the  vitelline ;  but  the  right  allantoic 
vein  and  the  right  vitelline  veins  soon  disappear,  while  the  long 


104: 


ANIMAL  PHYSIOLOGY. 


common  trunk  of  the  allantoic  and  vitelline  veins  {ductus  veno- 
sus)  passes  through  the  liver,  where  it  is  said  the  ductus  veno- 


FiG.  119.— Diagrams  of  the  aortic  arches  of  mammal  CLandois  and  StirUng,  after  Rathke). 
1.  Arterial  trunk  with  one  pair  of  arches,  and  an  indication  where  the  second  and  third 
pairs  will  develop.  2.  Ideal  stage  of  five  complete  arches  ;  the  fourth  clefts  are  shown  on 
the  left  side.  3.  The  two  anterior  pairs  of  arches  have  disappeared.  4.  Transition  to  the 
final  stage.  A.  aortic  arch  ;  ad,  dorsal  aorta  ;  ax,  subclavian  or  axillary  artery  ;  Ce,  ex- 
ternal carotid  ;  Ci.  internal  carotid  :  clB,  ductus  arteriosus  BotalU  ;  P,  pulmonary  artery  ; 
S,  subclavian  artery  ;  ta,  truncus  arteriosum  ;  v,  vertebral  artery. 

sus  gives  off  and  receives  branches.  The  ductus  venosus  Aran- 
tii  persists  throughout  life.  (Compare  the  various  figures  illus- 
trating the  circulation.) 


Fig.  120. — Diagram  illustrating  transformations  of  aortic  arches  in  a  lizard.  A  ;  a  snake,  B  ; 
a  bird.  C  ;  a  manunal,  D.  Seen  from  below.  (Haddon,  after  Rathke.)  a.  internal  caro- 
tid ;  h,  external  carotid  ;  c.  common  carotid.  A.  d,  ductus  Botalli  between  the  third  and 
fourth  arches  :  e,  right  aortic  arch  ;  /,  subclavian  ;  gr,  dorsal  aorta  :  7i,  left  aortic  arch  ; 
i,  pulmonary  artery  :  fc,  rudiment  of  the  ductus  Botalli  between  the  pulmonary  artery  and 
the  aortic  arches.  B.  d,  right  aortic  arch  :  e,  vertebral  artery  ;  /,  left  aortic  arch  ;  h. 
pulmonary  artery  :  t,  ductus  Botalli  of  the  latter.  C.  rf,  origin  of  aorta  ;  e,  fourth  arch  of 
the  right  side  (root  of  dorsal  aorta):  /,  right  subclavian:  g.  dorsal  aorta;  h,  left  subclavian 
(fourth  arch  of  the  left  side) ;  j,  pulmonary  artery  ;  k  and  ?,  right  and  left  ductus  BotaUi 
of  the  pulmonary  arteries.  D.  d.  origin  of  aorta  :  e.  fourth  arch  of  the  left  side  (root  of 
dorsal  aorta);  /,  dorsal  aorta:  g,  left  vertebral  artery:  /;,  left  subclavian;  i,  right  sub- 
clavian (fom-th  arch  of  the  right  side) ;  k,  right  vertebral  arterj- ;  U  continuation  of  the 
right  subclavian  :  m,  pulmonary  artery ;  n,  ductus  BotalH  of  the  latter  (usually  termed 
ductus  arteriosus). 


DEVELOPMENT  OF  THE  VASCULAR  SYSTEM. 


105 


With  the  development  of  the  phicenta  the  aHantoic  circula- 
tion renders  the  vitelline  subordinate,  the  vitelline  and  the  larger 
mesenteric  vein  forming  the  portal.  The  portal  vein  at  a  later 
period  joins  one  of  the  vence  advehentes  of  the  allantoic  vein. 

At  first  the  vena  cava  inferior  and  the  ductus  venosus  enter 
the  heart  as  a  common  trunk.  The  ductus  venosus  Arantii 
becomes  a  small  branch  of  the  vena  cava. 

The  allantoic  vein  is  finally  represented  in  its  degenerated 
form  as  a  solid  cord  {round  ligament),  the  entire  venous  sup- 
ply of  the  liver  being  derived  from  the  portal  vein. 

The  development  of  the  heart  has  already  been  traced  in  the 
fowl  up  to  a  certain  point.  In  the  mammal  its  origin  and  early 
progress  are  similar,  and  its  further  history  may  be  gathered 
from  the  following  series  of  representations. 

In  the  fowl  the  heart  shows  the  commencement  of  a  division 
into  a  right  and  left  half  on  the  third  day,  and  about  the 
fourth  week  in  man,  from  which  fact  alone  some  idea  may  be 
gained  as  to  the  relative  rate  of  development.     The  division 


Fig.  122. 


Fig.  121. 

Fig.  121.— Development  of  the  heart  in  the  human  embryo,  from  the  fourth  to  the  sixth  week. 

A.  Embryo  of  four  weeks  (K<illiker.  after  Coste).     B.  anterior.  C,  posterior  views  of  the 

heart  of  an  emliryo  of  six  weeks  (Kolliker,  after  Ecker).    a.  upiier  limit  of  buccal  cavity  ; 

c.  buccal  cavity  ;  h.  lies  between  the  ventral  ends  of  second  and  third  branchial  arches ; 

(I.  bu<l8  of  upiM-r  limbs  ;  /.  liver  ;  /.  intestine  :  1,  suiierior  vena  cava  ;  1',  left  superior  vena 

cava  :  1".  opening  of  inferior  vena  cava  ;  2,  2',  riffht  and  left  auricles  ;  3,  3'.  right  and  left 

ventricles  ;  4,  aortic  bulb. 
Fig.  122.— Human  embryo  of  about  three  weeks  (Allen  Thomson),    uv,  yelk-sac;  al,  allantois; 

am.  amnion  ;  a«,  anterior  extremity  ;  pe,  posterior  extremity. 


is  effected  by  the  outgrowth  of  a  septum  from  the  ventral  wall, 

whicli  rapidly  reaches  the  dorsal  side,  when  the  double  ven- 

licle  thus  formed  communicates  by  a  right  and  left  auriculo- 

ventricular  opening  with  the  large  and  as  yet  undivided  auricle. 


106  ANIMAL  PHYSIOLOGY. 

Later  an  incomplete  septum  forms  similar  divisions  in  the  auri- 
cle ;  the  aperture  {foramen  ovale)  left  by  the  imperfect  growth 
of  this  wall  persisting  throughout  foetal  life. 

The  Eustachian  valve  arises  on  the  dorsal  wall  of  the  right 
auricle,  between  the  vena  cava  inferior  and  the  right  and  left 
vense  cavse  superiores ;  but  in  many  mammals,  among  which  is 
man,  the  left  vena  cava  superior  disappears  during  foetal  life. 

For  the  present  we  may  simply  say  that  the  histories  of  the 
development  of  the  heart,  the  blood-vessels,  and  the  blood  itself 
are  closely  related  to  each  other,  and  to  the  nature  and  changes 
of  the  various  methods  in  which  oxygen  is  supplied  to  the  blood 
and  tissues,  or,  in  other  words,  to  the  development  of  the  respir- 
atory system. 


THE  DEVELOPMENT  OF  THE  UROGENITAL  SYSTEM. 

Without  knowing  the  history  of  the  organs,  the  anatomical 
relations  of  parts  with  uses  so  unlike  as  reproduction  on  the  one 
hand  and  excretion  on  the  other,  can  not  be  comprehended ;  nor, 
as  will  be  shortly  made  clear,  the  fact  that  the  same  part  may 
serve  at  one  time  to  remove  waste  matters  (urine)  and  at  an- 
other the  generative  elements. 

The  vertebrate  excretory  system  may  be  divided  into  three 
parts,  which  result  from  the  differentiation  of  the  primitive 
kidney  which  has  been  effected  during  the  slow  and  gradual 
evolution  of  vertebrate  forms  : 

1.  The  head-kidney  {pronephros). 

2.  The  Wolffian  body  {mesonephros). 

3.  The  kidney  proper,  or  metanephros. 

But  in  this  instance,  as  in  others,  to  some  of  which  allusion 
has  already  been  made,  these  three  parts  are  not  functional  at 
the  same  time.  The  pronephros  arises  from  the  anterior  part 
of  the  segmental  duct,  pronephric  duct,  duct  of  primitive  kid- 
ney, and  archinephric  duct,  and  in  the  fowl  is  apparent  on  the 
third  day;  but  the  pronephros  is  best  developed  in  the  ich- 
thyopsida  (fishes  and  amphibians).  A  vascular  process  from 
the  peritoneum  {glomerulus)  projects  into  a  dilated  section  of 
the  body  cavity,  which  is  in  part  separated  from  the  rest  of  this 
cavity  {ccdom).  This  process,  together  with  the  segmental 
duct,  now  coiled,  and  certain  short  tubes  developed  from  the 
original  duct,  make  up  the  pronephros.  The  segmental  duct 
opens  at  length  into  the  cloaca. 


THE   DEVELOPMENT   OP  THE   UROGENITAL  SYSTEM.      107 

The  mesonephros  (Wolffian  body),  though  largely  developed 
in  all  vertebrates  during  foetal  life,  is  not  a  persistent  excretory 
organ  of  adult  life. 


Fig.  123. — Diagrams  illustrating  development  of  pronephros  in  the  fowl  (Haddon).  ao,  aorta; 
b.  c.  body-cavity  ;  ep,  epiblast  with  its  epitrichial  (flattened)  layer  ;  hy,  hypoblast ;  in.  s, 
mesoblastic  somite  ;  n.  c,  neural  canal ;  nc/i,  notochord ;  p.  t,  pronephric  tubule  ;  so, 
somatic  ;  and  sp,  splanchnic,  mesoblast. 

In  the  fowl  recent  investigation  has  shown  that  the  Wolffian 
(segmental)  tubes  originate  from  outgrowths  of  the  Wolffian 


6    r     i 


f 


<s- 


Fi(,.  \Zi. 


Fio.  125. 


Fio.  121.— Rudimentary  primitive  kidney  of  embryonic  dog.  The  posterior  portion  of  the 
bfxly  of  the  embryo  is  seen  from  the  ventral  side,  covered  V)y  the  intestinal  layer  of  the 
yelk-Ka<r.  which  has  been  torn  away,  and  thrown  back  in  fi-ont  in  under  to  show  the  i)rimi- 
tlve  kidney  ducts  with  the  primitive  kidney  tubes  (a).  '',  priiiiitive  vertel)rH' ;  c,  dorsal 
medulla  ;  d.  pas.sage  into  the  pelvic  Intestinal  cavity.     (IIa>'<'ki-l,  after  Bischoff.) 

Fio.  I 2.'i.  Primitive  kidney  of  a  human  embrvo.  it.  th<'  uriiie-tiil)es  of  the  j)riinilive  kidney  ; 
V.  Wolffian  duct:  w'.  upper  end  of  the  i.itter  (MorgUKni's  hydatid);  in.  Millb-riMi.  duct; 
m'.  ujipi.-r  end  of  the  latter  (Fallopian  liydutidi;  y,  hermaphrodite  gland.     i.Mli'i  Kwbeil.) 

duct  and  also  from  an  iiitormcjdiate  cell-mass,  from  wliicli  lat- 
ter the  Malpighian  bodies  take  rise.    The  tubes,  at  first  not  con- 


108 


ANIMAL  PHYSIOLOGY. 


nected  with,  the  duct,  finally  join  it.  This  organ  is  continuous 
with  the  pronephros ;  in  fact,  all  three  (pronephros,  mesone- 
phros,  and  metanephros)  may  be  regarded  as  largely  continua- 
tions one  of  another. 

The  metanephros,  or  kidney  proper,  arises  from,  mesoblast 
at  the  posterior  part  of  the  Wolffian  body.     The  ureter  origi- 


FiG.  126. — Section  of  the  intermediate  cell-mass  of  fourth  day  (Foster  and  Balfour,  after  Wal- 
deyer).  1  x  160.  «i,  mesentery  ;  L,  somatopleure  ;  a',  portion  of  the  germinal  epithelium 
from  the  duct  of  Bliiller  is  formed  by  involution  ;  a,  thickened  portion  of  the  germinal 
epithelium,  in  which  the  primitive  ova  C  and  o  are  lying ;  E,  modified  mesoblast  which 
will  form  the  stroma  of  the  ovary  ;  WX,  Wolffian  body  ;  y.  Wolffian  duct. 

nates  first  from  the  hinder  portion  of  the  Wolffian  duct.  In 
the  fowl  the  kidney  tubules  bud  out  from  the  ureter  as  rounded 
elevations.  The  ureter  loses  its  connection  with  the  Wolffian 
duct  and  opens  independently  into  the  cloaca. 

The  following  account  will  apply  especially  to  the  higher 
vertebrates : 

The  segmental  (archinephric)  duct  is  divided  horizontally 
into  a  dorsal  or  Wolffian  (mesonephric)  duct  and  a  ventral  or 
MuUerian  duct.  The  Wolffian  duct,  as  we  have  seen,  develops 
into  both  ureter  and  kidney  proper. 

To  carry  the  subject  somewhat  further  back,  the  epithelium 
lining  the  ccelom  at  one  region  becomes  differentiated  into  col- 
umns or  cells  {germinal  epithelium)  which  by  involution  into 
the  underlying  mesoblast  forms  a  tubule  extending  from  before 
backward  and  in  close  relation  with  the  Wolffian  duct,  thus 


THE   DEVELOPMENT  OF  THE  UROGENITAL  SYSTEM.       109 


forming  the   Miillerian  duct  by  the  process  of  cleavage  and 
separation  referred  to  on  preceding  page. 


Fig.  127.— Diagrammatic  representation  of  the  genital  organs  of  a  human  embryo  previous  to 
sexual  distinction  (Allen  Thomson).  W,  Wolffian  body;  gc,  genital  cord;  rn,  Bliillerian 
duct ;  ir.  Wolffian  duct ;  ur/,  urogenital  sinus  ;  cp,  clitoris  or  penis ;  i.  intestine  ;  cl, 
cloaca  ;  Is,  part  from  which  the  scrotum  or  labia  majora  are  developed  ;  ot,  origin  of  the 
ovary  or  testicle  respectively  ;  x,  part  of  the  Wolffian  body  developed  later  into  the  coni 
vasculosi :  3,  ureter  ;  4,  bladder  ;  .5,  urachus. 

The  future  of  the  Miillerian  and  Wolffian  ducts  varies  ac- 
cording to  the  sex  of  the  embryo. 


Fio.  128.— Diagram  of  the  maiiiinalian  type  of  male  sexual  organs  Cafter  Quaiii).  Compare 
with  Figs.  127.  129.  C,  Cowt>cr"s  glanil  of  one  side  ;  cp,  cf)rpora  cavernosa  ])fnis,  cut  slmrt : 
f.  caput  (•i)iiiidymiH  ;  (/.  {.'ulMTiiaculurri  ;  j,  rectum  ;  hi,  hydatid  of  MorgaKni,  the  pcrsisti'iit 
ant*frior  end  of  the  .Mljlji-riaii  duct,  the  cf)njoint  post^-rior  end.s  of  which  form  Ihf  iilrnis 
rnatMMilirius  :  //r,  prostaU-  gland  ;  h,  Hcrotiirri  ;  hji,  corpus  spongiosum  nrclhrd' ;  /.testis 
(t<f(ticl<-i  in  the  place  of  it.s  original  formation.  The  dotted  line  indicates  tlw  <lin'<'ti(in  in 
which  the  t«'StiK  and  epididyiin'H  change  [dace  in  their  descent  from  the  abdomen  into  the 
scrotum  ;  rd,  van  deferenH ;  vli,  van  alierrans  ;  vh,  vesicula  seminalis ;  H',  remnants  of 
Wolffian  body  (the  organ  of  (UraMiiH  or  paradidymiH  of  Waldeyer; ;  'i,  4,  .'>,  as  in  Fig.  129. 


110 


ANIMAL  PHYSIOLOGY. 


In  the  male  the  Wolffian  duct  persists  as  the  vas  deferens  ; 
in  the  female  it  remains  as  a  rudiment  in  the  region  near  the 
ovary  (hydatid  of  Morgagni).  In  the  female  the  Mtillerian 
duct  becomes  the  oviduct  and  related  parts  (uterus  and  vagina) ; 
in  the  male  it  atrophies.  One,  usually  the  right,  also  atrophies 
in  female  birds.  The  sinus  pocularis  of  the  iDrostate  is  the  rem- 
nant in  the  male  of  the  fused  tubes. 

The  various  forms  of  the  generative  apparatus  derived  from 
the  Mtillerian  ducts,  as  determined  by  different  degrees  of  fu- 
sion, etc.,  of  parts,  may  be  learned  from  the  accompanying 
figures. 

In  both  sexes  the  most  posterior  portion  of  the  Wolffian 
duct  gives  rise  to  the  metanephros,  or  what  becomes  the  perma- 


FiG.  129. — Diagram  of  the  mammalian  type  of  female  sexual  organs  (after  Quain).  The  dotted 
lines  in  one  figure  indicate  functional  organs  in  the  other.  C,  gland  of  Bartholin  (Cowper's 
gland) ;  c.  c,  corpus  cavernosuni  elitoridis ;  clG,  remains  of  the  left  Wolffian  duct,  which 
may  persist  as  the  duct  of  Gaertner ;  /,  abdominal  opening  of  left  Fallopian  tube ;  g, 
round  ligament  (corresponding  to  the  gubernaculum) ;  h,  hymen  ;  i,  rectum  ;  I,  labium  ; 
m,  cut  FaOopian  tube  (oviduct,  or  Miillerian  duct)  of  the  right  side  ;  n,  nynipha ;  o,  left 
ovary  ;  po.  parovarium  ;  sc,  vascular  bulb  or  corpus  spongiosum  ;  u,  uterus ;  v,  vulva  ; 
va,  vagina ;  W,  scattered  remains  of  Wolffian  tubes  (paroophoron) ;  iv,  cut  end  of  van- 
ished right  Wolffian  duct ;  3,  ureter ;  4,  bladder  passing  below  into  the  uretha ;  5,  urachus, 
or  remnant  of  stalk  of  aUantois. 


nent  kidney  and  ureter ;  in  the  male  also  to  the  vas  deferens, 
testicle,  vas  aberrans,  and  seminal  vesicle. 

The  ovary  has  a  similar  origin  to  the  testicle  ;  the  germinal 
epithelium  furnishing  the  cells,  which  are  transformed  into 
Graafian  follicles,  ova,  etc.,  and  the  mesoblast  the  stroma  in 
which  these  structures  are  imbedded. 

In  the  female  the  parovarium  remains  as  the  representative 
of  the  atrophied  Wolffian  body  and  duct. 

The  bladder  and  urachus  are  both  remnants  of  the  formerly 
extensive  aUantois.     The  final  forms  of  the  genito-urinary  or- 


THE  DEVELOPMENT  OF  THE  UROGENITAL  SYSTEM.      m 

gans  arise  by  differentiation,  fusion,  and  atrophy:  thus,  the 
cloaca  or  common  cavity  of  the  genito-urinary  ducts  is  divided 
by  a  septum  (the  perineum  externally)  into  a  genito-urinary 
and  an  intestinal  (anal)  part ;  the  j)enis  in  the  male  and  the 
corresponding  clitoris  in  the  female  appear  in  the  region  of  the 
cloaca,  as  outgrowths  which  are  followed  by  extension  of  folds 
of  integument  that  become  the  scrotum  in  the  one  sex  and  the 
labia  in  the  other. 

The  urethra  arises  as  a  groove  in  the  under  surface  of  the 
penis,  which  becomes  a  canal.  The  original  opening  of  the 
urethra  was  at  the  base  of  the  penis. 


ALL 


ALL^ 


^ 


CLi 
Fig.  130.  Fig.  131. 


Fig.  1.32. 

Figs.  130  to  1.33.— Diagrams  illustrating  the  evolution  of  the  posterior  passages  (after  Landoia 
and  Stirling). 

Fig.  130. — Allantois  continuous  with  rectum. 

Fig.  131.— Cloaca  formed. 

Fig.  132.— Early  condition  in  male,  before  the  closure  of  the  folds  of  the  groove  on  the  poste- 
rior sidf"  of  the  penis. 

Fig.  1-3:5.— Early  female  condition. 

A,  commencement  of  proctodceum  ;  ALL,  allantois  ;  B,  bladder  ;  C,  penis ;  CL,  cloaca  ; 
J/,  Miillerian  duct ;  B,  rectum :  U,  urethra ;  S,  vestibule ;  SU,  urogenital  sinus ;  V,  vas 
deferens  in  Fig.  132,  vagina  in  Fig.  133. 

In  certain  cases  development  of  these  parts  is  arrested  at 
various  stages,  from  which  result  abnormalities  frequently  re- 
quinng  interference  by  the  surgeon. 

The  accounts  of  the  previous  chapters  do  not  complete  the 
history  of  development.  Certain  of  the  remaining  subjects 
that  are  of  special  interest,  from  a  physiological  point  of  view, 
will  be  referred  to  again;  and  in  the  mean  time  we  shall 
consider  rather  briefly  some  of  the  physiological  problems  of 
this  subject  to  which  scant  reference  has  as  yet  been  made. 
Though  the  pliysiology  of  reproduction  is  introduced  here,  so 
that  ties  of  natural  connection  may  not  be  severed,  it  may 
very  well  be  omitted  by  the  student  who  is  dealing  with  embry- 


112 


ANIMAL  PHYSIOLOGY. 
A 


Fig.  134.— "Various  forms  of  mammalian  uteri.  A.  Ornithorhynchus.  B.  Didelphys  dorsigera. 
C.  Phalangista  vulpina.  D.  Double  uterus  and  vagina ;  human  anomaly.  E.  Lepus  cuni- 
culus  (rabbit),  utei-us  duplex.  F.  Uterus  bicornis.  G.  Utenis  bipartitus.  H.  Uterus 
simplex  (human),  o,  anus  ;  cl,  cloaca  ;  o.  d,  oviduct ;  o.  t,  os  tincae  (os  uteri) ;  ov,  ovary  ; 
r,  rectum  ;  s,  vaginal  septum  ;  u.  b,  urinary  bladder  ;  ur,  ureter  ;  ur.  o,  orifice  of  same  ; 
us,  m'ogenital  sinus  ;  ut,  uterus  ;  v,  vagina  ;  v.  c,  vaginal  caecum  (Haddon). 

ology  for  tlie  first  time,  and  in  any  case  slionld  be  read  again 
after  the  other  functions  of  the  body  have  been  studied. 


The  Physiological  Aspects  of  Development. 

According  to  that  law  of  rhythm  which,  as  we  have  seen, 
prevails  throughout  the  world  of  animated  nature,  there  are 
periods  of  growth  and  progress,  of  quietude  and  arrest  of  devel- 
opment ;  and  in  vertebrates  one  of  the  most  pronounced  epochs 
— in  fact,  the  most  marked  of  all — is  that  by  which  the  young 
organism,  through  a  series  of  rapid  stages,  attains  to  sexual 
maturity. 

While  the  growth  and  development  of  the  generative  or- 
gans share  to  the  greatest  degree  in  this  progress,  other  parts  of 
the  body  and  the  entire  being  participate. 

So  great  is  the  change  that  it  is  common  to  indicate,  in  the 
case  of  the  human  subject,  the  developed  organism  by  a  new 
name— the  "  boy  "  becomes  the  "  man,"  the  "  girl "  the  "woman.'' 
Relatively  this  is  by  far  the  most  rapid  and  general  of  all  the 
transformations  the  organism  undergoes  during  its  extra-uter- 
ine life.  In  this  the  entire. body  takes  part,  but  very  unequally. 
The  increase  in  stature  is  not  proportionate  to  the  increase 
in  weight,  and  the  latter  is  not  so  great  as  the  change  in  form. 
The  modifications  of  the  organism  are  localized  and  yet  affect 
the  whole  being.     The  outlines  become  more  rounded ;  the  pel- 


THE  DEVELOPMENT  OF  THE   UROGENITAL   SYSTEM.      II3 

vis  in  females  alters  in  shape ;  not  only  do  the  generative  organs 
themselves  rapidly  undergo  increased  development,  but  certain 
related  glands  (mammse)  participate ;  hair  appears  in  certain 
regions  of  the  body ;  the  larynx,  especially  in  the  male,  under- 
goes enlargement  and  changes  in  the  relative  size  of  parts,  re- 
sulting in  an  alteration  of  voice  (breaking  of  the  voice),  etc. — 
all  in  conformity  with  that  excess  of  nutritive  energy  which 
marks  this  biological  epoch. 

Correlated  with  these  physical  changes  are  others  belonging 
to  the  intellectual  and  moral  (psychic)  nature  equally  impor- 
tant, and,  accordingly,  the  future  being  depends  largely  on  the 
full  and  unwarped  developments  of  these  few  years. 

Sexual  maturity,  or  the  capacity  to  furnish  ripe  sexual  ele- 
ments (cells),  is  from  the  biological  standpoint  the  most  impor- 
tant result  of  the  onset  of  that  period  termed,  as  regards  the 
human  species,  puberty. 

The  age  at  which  this  epoch  is  reached  varies  with  race, 
sex,  climate,  and  the  moral  influences  which  envelop  the  indi- 
vidual. In  temperate  regions  and  with  European  races  i3u- 
berty  is  reached  at  from  about  the  thirteenth  to  the  eighteenth 
year  in  the  female,  and  rather  later  in  the  male,  in  whom  de- 
velopment generally  is  somewhat  slower. 

Menstruation  and  Ovulation. 

In  all  vertebrates,  at  periods  recurring  with  great  regu- 
larity, the  generative  organs  of  the  female  manifest  unusual 
activity.  This  is  characterized  by  increased  vascularity  of  the 
ovary  and  adjacent  parts ;  with  other  changes  dependent  on 
this,  and  that  heightened  nerve  influence  which,  in  the  verte- 
brate, seems  to  be  insejiarable  from  all  important  functional 
changes.  Ovulation  is  the  maturation  and  discharge  of  ova 
from  the  Graafian  follicles.  The  latter,  reaching  the  exterior 
zone  of  the  ovary,  becf^ming  distended  and  thinned,  burst  ex- 
ternally and  thus  free  the  ovum.  The  follicles  being  very  vas- 
cular at  this  j^eriod,  blood  escapes,  owing  to  this  rupture,  into 
the  emptied  capsule  and  clots;  and  as  a  result  of  organization 
and  subsequent  degeneration  undergoes  a  certain  series  of 
changes  dependent  on  the  condition  of  the  ovary  and  adjacent 
parts,  which  varies  according  as  the  ovum  has  been  fertilized 
or  not.  When  fertilization  occuirs  the  Graafian  follicle  under- 
goes changes  of  a  more  marked  and  lasting  character,  becom- 
ing a  true  corpus  luteum  of  pregnancy. 
8 


114 


ANIMAL  PHYSIOLOGY. 


Tlie  ovum,  in  the  fowl  is  fertilized  in  tlie  upper  part  of  tlie 
o^T.duct ;  in  the  mammal  mostly  in  this  region  also,  as  is  shown 
by  the  site  of  the  embryos  in  those  groups  of  animals  with  a 
two-horned  uterus,  and  the  occasional  occurrence  of  tubal  preg- 
nancy in  woman.  But  this  is  not,  in  the  human  subject  at 
least,  invariably  the  site  of  impregnation.  After  the  ovum  has 
been  set  free,  as  above  described,  it  is  conveyed  into  the  ovi- 
duct (Fallopian  tube),  though  exactly  how  is  still  a  matter  of 
dispute :  some  holding  that  the  current  produced  by  the  action 
of  the  ciliated  cells  of  the  Fallopian  tube  suffices ;  others  that 
the  o^nim  is  grasped  by  the  fimbriated  extremity  of  the  tube  as 
part  of  a  co-ordinated  act.  It  is  likely,  as  in  so  many  other 
instances,  that  both  -sdews  are  correct  but  partial ;  that  is  to 
say,  both  these  methods  are  employed.  The  columnar  ciliated 
cells,  lining  the  oviduct,  act  so  as  to  produce  a  current  in  the 
direction  of  the  uterus,  thus  assisting  the  ovum  in  its  passage 
toward  its  final  resting  place. 

Menstmation. — As  a  part  of  the  general  acti^dty  occurring 
at  this  time,  the  uterus  manifests  certain  changes,  chiefly  in 
its  internal  mucous  lining,  in  which  thickening  and  increased 


Fig.  135.— Diagram  of  the  human  uterus  just 
before  menstruation.  The  shaded  por- 
tion represents  the  mucous  membrane 
(Hart  and  Barbour,  after  J.  Williams). 


Fig.  136. — Uterus  after  menstraation  has  just 
ceased.  The  cavity  of  the  body  of  the 
uterus  is  supposed  to  have  been  deprived 
of  mucous  membrane  (J.  Williams). 


vascularity  are  prominent.     A  flow  of  blood  from  the  uterus 
in  the  form  of  a  gentle  oozing  follows ;  and  as  the  superficial 


THE   DEVELOPMENT   OF   THE   UROGENITAL  SYSTEM.       115 

parts  of  the  mucous  lining  of  the  uterus  undergo  softening 
and  fatty  degeneration,  they  are  thrown  off  and  renewed  at 
these  periods  {catamenia,  menses,  etc.),  provided  pregnancy 
does  not  take  place.  In  mammals  below  man,  in  their  nat- 
ural state,  pregnancy  does  almost  invariably  take  place  at 
such  times,  hence  this  exalted  activity  of  the  mucous  coat  of 
the  uterus,  in  preparation  for  the  reception  and  nutrition  of 
the  ovum,  is  not  often  in  vain.  In  the  human  subject  the 
menses  appear  monthly ;  pregnancy  may  or  may  not  occur,  and 
consequently -there  may  be  waste  of  nature's  forces;  though 
there  is  a  certain  amount  of  evidence  that  menstruation  does 
not  wholly  represent  a  loss ;  but  that  it  is  largely  of  that  char- 
acter among  a  certain  class  of  women  is  only  too  evident.  As 
can  be  readily  understood,  the  catamenial  flow  may  take  place 
prior  to,  during,  or  after  the  rupture  of  the  egg-capsule. 

As  the  uterus  is  well  supplied  with  glands,  during  this 
period  of  increased  functional  activity  of  its  lining  membrane, 
mucus  in  considerable  excess  over  the  usual  quantity  is  dis- 
charged ;  and  this  phase  of  activity  is  continued  should  preg- 
nancy occur. 

All  the  parts  of  the  generative  organs  are  supplied  with 
muscular  tissue,  and  with  nerves  as  well  as  blood-vessels,  so 
that  it  is  possible  to  understand  how,  by  the  influence  of  nerve- 
centers,  the  various  events  of  ovulation,  menstruation,  and 
those  that  follow  when  pregnancy  takes  place,  form  a  related 
series,  very  regular  in  their  succession,  though  little  prominent 
in  the  consciousness  of  the  individual  animal  when  normal. 

The  Nutrition  of  the  Ovum  (oosperm). 

This  will  be  best  understood  if  it  be  remembered  that  the 
ovum  is  a  cell,  undifferentiated  in  most  directions,  and  thus  a 
sort  of  amoeboid  organism.  In  the  fowl  it  is  known  that  the 
cells  of  the  primitive  germ  devour,  amoeba-like,  the  yelk-cells, 
while  in  the  mammalian  oviduct  the  ovum  is  surrounded  by 
abundance  of  proteid,  which  is  doubtless  utilized  in  a  somewhat 
similar  fashion,  as  also  in  the  uterus  itself,  until  the  embryonic 
membranes  have  formed.  To  speak  of  the  ovum  being  nour- 
ished by  diffusion,  and  es])ecially  by  osmosis,  is  an  unnecessary 
assumption,  and,  as  we  believe,  at  variance  Avith  fundamental 
principles ;  for  we  doubt  much  whether  any  vital  process  is 
one  of  pure  osmosis.  As  soon  as  the  yelk-sac  and  allantois 
have  been  formed,  nutriment  is  derived  in  great  part  through 


116  ANIMAL  PHYSIOLOGY. 

the  vessel- walls,  which,  it  will  be  remembered,  are  differentia- 
ted from  the  cells  of  the  mesoblast,  and,  it  may  well  be  as- 
sumed, have  not  at  this  early  stage  entirely  lost  their  amoeboid 
character.  The  blood-vessels  certainly  have  a  respiratory  func- 
tion, and  suffice,  till  the  more  complicated  villi  are  formed. 
The  latter  structures  are  in  the  main  similar  in  build  to  the 
villi  of  the  alimentary  tract,  and  are  adapted  to  being  sur- 
rounded by  similar  structures  of  maternal  origin.  Both  the 
maternal  crypts  and  the  fcetal  villi  are,  though  complementary 
in  shape,  all  but  identical  in  minute  structure-  in  most  in- 
stances. In  each  case  the  blood-vessels  are  covered  superfi- 
cially by  cells  which  we  can  not  help  thinking  are  essential  in 
nutrition.  The  villi  are  both  nutritive  and  respiratory.  It  is 
no  more  difficult  to  understand  their  function  than  that  of  the 
cells  of  the  endoderm  of  a  polyp,  or  the  epithelial  coverings  of 
lungs  or  gills. 

Experiment  proves  that  there  is  a  respiratory  interchange 
of  gases  between  the  maternal  and  fcetal  blood  which  nowhere 
mingle  physically.  The  same  law  holds  in  the  respiration  of 
the  foetus  as  in  the  mammals.  Oxygen  passes  to  the  region 
where  there  is  least  of  it,  and  likewise  carbonic  anhydride.  If 
the  mother  be  asphyxiated  so  is  the  foetus,  and  indeed  more 
rapidly  than  if  its  own  umbilical  vessels  be  tied,  for  the  mater- 
nal blood  in  the  first  instance  abstracts  the  oxygen  from  that 
of  the  foetus  when  the  tension  of  this  gas  becomes  lower  in  the 
maternal  than  in  the  foetal  blood  ;  the  usual  course  of  affairs 
is  reversed,  and  the  mother  satisfies  the  oxygen  hunger  of  her 
own  blood  and  tissues  by  withdrawing  that  which  she  recently 
supplied  to  the  foetus.  It  will  be  seen,  then,  that  the  embryo  is 
from  the  first  a  parasite.  This  explains  that  exhaustion  which 
pregnancy,  and  especially  a  series  of  gestations,  entails.  True, 
nature  usually  for  the  time  meets  the  demand  by  an  excess  of 
nutritive  energy :  hence  many  persons  are  never  so  vigorous  in 
appearance  as  when  in  this  condition ;  often,  however,  to  be  fol- 
lowed by  corresponding  emaciation  and  senescence.  The  full 
and  frequent  respirations,  the  bounding  pulse,  are  succeeded  by 
reverse  conditions  ;  action  and  reaction  are  alike  present  in  the 
animate  and  inanimate  worlds.  Moreover,  it  falls  to  the  parent 
to  eliminate  not  only  the  waste  of  its  own  organism  but  that  of 
the  foetus  ;  and  not  infrequently  in  the  human  subject  the  over- 
wrought excretory  organs,  especially  the  kidneys,  fail,  entailing 
disastrous  consequences. 

The  digestive  functions  of  the  embryo  are  naturally  inact- 


THE   DEVELOPMENT  OP  THE  UROGENITAL  SYSTEM.      117 

ire,  the  blood  being  supplied  with  all  its  needful  constituents 
through  the  placenta  by  a  much  shorter  process ;  indeed,  the 
placental  nutritive  functions,  so  far  as  the  fcetus  is  concerned 
may  be  compared  with  the  removal  of  already  digested  material 
from  the  alimentary  canal,  though  of  course  only  in  a  general 
way.  During  foetal  life  the  digestive  glands  are  developing, 
and  at  the  time  of  birth  all  the  digestive  juices  are  secreted  in 
an  efficient  condition,  though  only  relatively  so,  necessitating  a 
special  liquid  food  (milk)  in  a  form  in  which  all  the  constituents 
of  a  normal  diet  are  provided,  easy  of  digestion. 


frL~th^^f^  «T'°1'^'^  embryos  from  the  second  to  the  fifteenth  week  (natural  size)  seen 
from  the  left  side,  the  arched  back  turned  t«jward  the  right.    (Priucii)all\-  after  Ecker^ 
5lil""^Ar'"i'i7''  o?  I''  days  ;  in,  of  3  weeks  ;  JV,  of  4  weeks     V,  of  5  weeks  •  V^^ 
weeka  ;  V  U,  of  7  weeks  ;  Vlll,  of  8  weeks  ;  XU,  of  12  weeks  ;  XV,  of  15  weeks      ' 

Bile,  inspissated  and  mixed  with  the  dead  and  cast-off  epi- 
thelium of  the  alimentary  tract,  is  abundant  in  the  intestine  at 
birth  in  the  human  subject ;  but  bile  is  to  be  regarded  perhaps 
rather  in  the  light  of  an  excretion  than  as  a  digestive  fluid. 
The  .skin  and  kidneys,  thougli  not  functionless,  are  rendered 
unnecessary  in  great  part  by  the  fact  that  waste  can  be  and  is 
withdrawn  by  the  placenta,  which  proves  to  be  a  nutritive,  re- 


118  ANIMAL  PHYSIOLOGY. 

spiratory,  and  excretory  organ ;  it  is  in  itself  a  sort  of  abstract 
and  brief  chronicle  of  the  whole  physiological  story  in  foetal  life. 

All  of  the  foetal  organs,  especially  the  muscles,  abound  in  an 
animal  starch  (glycogen),  which  in  some  way,  not  well  under- 
stood, forms  a  reserve  fund  of  nutritive  energy  which  is  pretty 
well  used  up  in  the  earlier  months  of  pregnancy.  We  may 
suppose  that  the  amoeboid  cells — all  the  undifferentiated  cells 
of  the  body — feed  on  it  in  primitive  fashion ;  and  it  will  not 
be  forgotten  that  the  older  the  cells  become,  the  more  do  they 
depart  from  the  simpler  habits  of  their  earlier,  cruder  existence ; 
hence  the  disappearance  of  this  substance  in  the  later  months 
of  foetal  life. 

In  one  respect  the  foetus  closely  resembles  the  adult:  it 
draws  the  pabulum  for  all  its  various  tissues  from  blood  which 
itself  may  be  regarded  as  the  first  completed  tissue.  We  are, 
accordingly,  led  to  inquire  how  this  river  of  life  is  distributed ; 
in  a  word,  into  the  nature  of  the  foetal  circulation. 

Foetal  Circulation. — The  blood  leaves  the  placenta  by  the  um- 
bilical vein,  reaches  the '  inferior  vena  cava,  either  directly  (by 
the  ductus  venosus),  or,  after  first  passing  to  the  liver  (by  the 
vencE  advehentes,  and  returning  by  the  venm  revehentes),  and 
proceeds,  mingled  with  the  blood  returning  from  the  lower  ex- 
tremities, to  the  right  auricle.  This  blood,  though  far  from 
being  as  arterial  in  character  as  the  blood  after  birth,  is  the 
best  that  reaches  the  heart  or  any  part  of  the  organism.  After 
arriving  at  the  right  auricle,  being  dammed  back  by  the  Eus- 
tachian valve,  it  avoids  the  right  ventricle,  and  shoots  on  into 
the  left  auricle,  passing  thence  into  the  left  ventricle,  from 
which  it  is  sent  into  the  aorta,  and  is  then  carried  by  the  great 
trunks  of  this  arch  to  the  head  and  upper  extremities.  The 
blood  returning  from  these  parts  passes  into  the  right  auricle, 
then  to  the  corresponding  ventricle  and  thence  into  the  pul- 
monary artery;  but,  finding  the  branches  of  this  vessel  un- 
opened, it  takes  the  line  of  least  resistance  through  the  ductus 
arteriosus  into  the  aortic  arch  beyond  the  point  where  its  great 
branches  emerge.  It  will  be  seen  that  the  blood  going  to  the 
head  and  upper  parts  of  the  body  is  greatly  more  valuable  as 
nutritive  pabulum  than  the  rest,  especially  in  the  quantity  of 
oxygen  it  contains ;  that  the  blood  of  the  foetus,  at  best,  is  rela- 
tively ill-supplied  with  this  vital  essential ;  and  as  a  result  we 
find  the  upper  (anterior  in  quadrupeds)  parts  of  the  foetus  best 
developed,  and  a  decided  resemblance  between  the  mammalian 
foetus  functionally  and  the  adult  forms  of  reptiles  and  kindred 


THE  DEVELOPMENT  OF  THE  UROGENITAL  SYSTEM.      119 


groups  of  the  lower  vertebrates.     But  this  condition  is  well 
enough  adapted  to  the  general  ends  to  be  attained  at  this  pe- 


Pulmonary  Arf. 

Foramen  Ovale 

Husiachian  Valve. ... 
Right  Auric.  -  Vent.  Opening. 


Branches  of  the 
Uriihilical  Vein, 
to  the  Liver. 


Bladder. 


Pulmonary  Art. 
■■  Left  Auricle. 
..  Left  Aicric.  -  Vent. 

Opening. 


Hepatic  Vein. 


Ductus  Venostts. 


Internal  Iliac  Arteries. 
Fin.  138.-Diaj^am  of  the  foetal  circulation  (Flint). 


120  ANIMAL  PHYSIOLOGY. 

riod— the  nourishment  of  structures  on  the  way  to  a  higher 
path  of  progress. 

As  embryonic  maturity  is  being  reached,  preparation  is  made 
for  a  new  form  of  existence ;  so  it  is  found  that  the  Eustachian 
valve  is  less  prominent  and  the  foramen  ovale  smaller. 

Parturition. 

■  All  the  efforts  that  have  hitherto  been  made  to  determine 
the  exact  cause  of  the  result  of  that  series  of  events  which  make 
up  parturition  have  failed.  This  has  probably  been  owing  to 
an  attempt  at  too  simple  a  solution.  The  foetus  lies  surrounded 
(protected)  by  fluid  contained  in  the  amniotic  sac.  For  its  expul- 
sion there  is  required,  on  the  one  hand,  a  dilatation  of  the  uter- 
ine opening  {os  uteri),  and,  on  the  other,  a  vis  a  tergo.  The  lat- 
ter is  furnished  by  the  contractions  of  the  uterus  itself,  aided  by 
the  simultaneous  action  of  the  abdominal  muscles.  Through- 
out the  greater  part  of  gestation  the  uterus  experiences  some- 
what rhythmical  contractions,  feeble  as  compared  with  the 
final  ones  which  lead  to  expulsion  of  the  foetus,  but  to  be  regard- 
ed as  of  the  same  character.  With  the  growth  and  functional 
development  of  other  organs,  the  placenta  becomes  of  less  con- 
sequence, and  a  fatty  degeneration  sets  in,  most  marked  at  the 
periphery,  usually  where  it  is  thinnest  and  of  least  use.  It  does 
not  seem  rational  to  believe  that  the  onset  of  labor  is  referable 
to  any  one  cause,  as  has  been  so  often  taught ;  but  rather  that  it 
is  the  final  issue  to  a  series  of  processes  long  existing  and  grad- 
ually, though  at  last  rapidly,  reaching  that  climax  which  seems 
like  a  vital  storm.  The  law  of  rhythm  affects  the  nervous  sys- 
tem as  others,  and  upon  this  depends  the  direction  and  co-ordi- 
nation of  those  many  activities  which  make  up  parturition. 
We  have  seen  that  throughout  the  whole  of  foeta^l  life  changes 
in  one  part  are  accompanied  by  corresponding  changes  in  oth- 
ers ;  and  in  the  final  chapter  of  this  history  it  is  not  to  be  ex- 
pected that  this  connection  should  be  severed,  though  it  is  not 
at  present  possible  to  give  the  evolution  of  this  process  with 
any  more  than  a  general  approach  to  probable  correctness. 

Changes  in  the  Circulation  after  Birth. 

When  the  new-born  mammal  takes  the  first  breath,  effected 
by  the  harmonious  action  of  the  respiratory  muscles,  excited 
to  action  by  stimuli  reaching  them  from  the  nerve-center  (or 


THE  DEVELOPMENT  OF   THE  UROGENITAL  SYSTEM.      121 

centers)  which  preside  over  respiration,  owing  to  its  being 
roused  into  action  by  the  lack  of  its  accustomed  supply  of 
oxygen,  the  hitherto  solid  lungs  are  expanded ;  the  pulmonary 
vessels  are  rendered  permeable,  hence  the  blood  now  takes  the 
path  of  least  resistance  along  them,  as  it  formerly  did  through 
the  ductus  arteriosus.  The  latter,  from  lack  of  use,  atrophies 
in  most  instances.  The  blood,  returning  to  the  left  auricle  of 
the  heart  from  the  lungs  in  increased  volume,  so  raises  the 
pressure  in  this  chamber  that  the  stream  that  formerly  flowed 
through  the  foramen  ovale  from  the  right  auricle  is  opposed 
by  a  force  equal  to  its  own,  if  not  greater,  and  hence  passes  by 
an  easier  route  into  the  right  ventricle.  The  fold  that  tends  to 
close  the  foramen  ovale  grows  gradually  over  the  latter,  so  that 
it  usually  ceases  to  exist  in  a  few  days  after  birth. 

At  birth,  ligature  of  the  umbilical  cord  cuts  off  the  placental 
circulation ;  hence  the  ductus  venosus  atrophies  and  becomes  a 
mere  ligament. 

The  placenta,  being  now  a  foreign  body  in  the  uterus,  is  ex- 
pelled, and  this  organ,  by  the  contractions  of  its  walls,  closes  the 
ruptured  and  gaping  vessels,  thus  providing  against  hsemor- 
rhage. 

Coitus  between  the  Sexes. 

In  all  the  higher  vertebrates  congress  of  the  sexes  is  essential 
to  bring  the  male  sexual  product  into  contact  with  the  ovum. 


F'lO.  139.— Sfctif)n  of  erfM.-tile  tissuf  ff'adiat).    ri,  traJieculse  of  connective  tissue,  with  elastic 
flbere,  and  bundleH  of  plain  niuHCular  tissue  (c) ;  b,  venous  spaces  (Scliiifcn. 


122 


ANIMAL  PHYSIOLOGY. 


Erection  of  the  penis  results  from  the  conveyance  of  an 
excess  of  blood  to  the  organ,  owing  to  dilation  of  its  arteries, 
and  the  retention  of  this  blood  within  its  caverns. 

The  structure  of  the  penis  is  peculiar,  and,  for  the  details  of 
the  anatomy  of  both  the  male  and  female  generative  organs, 
the  student  is  referred  to  works  on  this  subject ;  suffice  it  to 
say  that  it  consists  of  erectile  tissue,  the  chief  characteristic  of 
which  is  the  opening  of  the  capillaries  into  cavernous  venous 
spaces  {sinuses)  from  which  the  veinlets  arise ;  with  such  an 
arrangment  the  circulation  must  be  very  slow — the  inflow 
being  greatly  in  excess  of  the  outflow — apart  altogether  from 
the  compressive  action  of  certain  muscles  connected  with  the 
organ.  As  previously  explained,  the  spermatozoa  originate  in 
the  seminal  tubes,  from  which  they  find  their  way  to  the 


Fig.  140.— Section  of  parts  of  three  seminiferous  tubules  of  the  rat  (Schafer).  a,  with  the 
spermatozoa  least  advanced  in  development ;  b,  more  a,dvanced  ;  c,  containing  fuUy  de- 
veloped spermatozoa.  Between  the  tubules  are  seen  strands  of  interstitial  cells,  with 
blood-vessels  and  lymph-spaces. 

seminal  vesicles  or  receptacles  for  semen  till  required  to  be 
discharged.  The  spermatozoa  as  they  mature  are  forced  on  by 
fresh  additions  from  behind  and  by  the  action  of  the  ciliated 
cells  of  the  epididymis,  together  with  the  wave-like  (peristaltic) 
action  of  the  vas  deferens.  Discharge  of  semen  during  coitus 
is  effected  by  more  vigorous  peristaltic  action  of  the  vas  defer- 
ens and  the  seminal  vesicles,  followed  by  a  similar  rhythmical 
action  of  the  bulbo-cavernosus  and  ischio-cavernosus  muscles, 
by  which  the  fluid  is  forcibly  ejaculated. 

Semen  itself,  though  composed  essentially  of  spermatozoa. 


THE   DEVELOPMENT  OF  THE   UROGENITAL  SYSTEM.      123 

is  mixed  with  the  secretions  of  the  vas  deferens,  of  the  seminal 
vesicles,  of  Cowper's  glands,  and  of  the  prostate.  Chemically 
it  is  neutral  or  alkaline  in  reaction,  highly  albuminous,  and 
contains  nuclein,  lecithen,  cholesterin,  fats,  and  salts. 

The  movements  of  the  male  cell,  owing  to  the  action  of  the 
tail  (cilium),  suflBce  of  themselves  to  convey  them  to  the  ovi- 


FlG.  141. — Left  broad  ligament.  Fallopian  tube,  ovary,  and  parovarium  in  the  human  subject 
(Henle).  «,  uterus  ;  i,  isthmus  of  Fallopian  tube  ;  a,  ampulla  ;  /,  fimbriated  end  of  the 
tube,  with  the  parovarium  to  its  right ;  o.  ovary  ;  o.  I,  ovarian  ligament. 

ducts :  but  there  is  little  doubt  that  during  or  after  sexual  con- 
gress there  is  in  the  female,  even  in  the  human  subject,  at  least 


Fio.  142.— UteruH  and  ovaries  of  the  sow,  8emi-dia(|rammatic  (after  Dalton).    o,  ovary  ;  H, 
Fallopian  tube  ;  h,  horn  of  the  uterus  ;  b,  bfxiy  of  the  uterus  ;  v,  vagina. 


in  many  cases,  a  retrograde  peristalsis  of  the  uterus  and  ovi- 
ducts which  would  tend  to  overcome  the  results  of  the  activity 


124:  ANIMAL  PHYSIOLOGY. 

of  the  ciliated  cells  lining  the  oviduct.  It  is  known  that  the 
male  cell  can  survive  in  the  female  organs  of  generation  for 
several  days,  a  fact  not  difficult  to  understand,  from  the  method 
of  nutrition  of  the  female  cell  (ovum) ;  for  we  may  suppose 
that  both  elements  are  not  a  little  alike,  as  they  are  both 
slightly  modified  amoeboid  organisms. 

Nervous  Mechanism. — Incidental  reference  has  been  made  to 
the  directing  influence  of  the  nervous  system  over  the  events 
of  reproduction ;  especially  their  subordination  one  to  another 
to  bring  about  the  general  result.  These  may  now  be  consid- 
ered in  greater  detail. 

Most  of  the  processes  in  which  the  nervous  system  takes 
part  are  of  the  nature  of  reflexes,  or  the  result  of  the  automa- 
ticity  (independent  action)  of  the  nerve-centerSj,  increased  by 
some  afferent  (ingoing)  impressions  along  a  nerve-path.  It  is 
not  always  possible  to  estimate  the  exact  share  each  factor 
takes,  which  must  be  highly  variable.  Certain  experiments 
have  assisted  in  making  the  matter  clear.  It  has  been  found 
that,  if  in  a  female  dog,  the  spinal  cord  be  divided  when  the 
animal  is  still  a  puppy,  menstruation  and  impregnation  may 
occur.  If  the  same  experiment  be  performed  on  a  male  dog, 
erection  of  the  penis  and  ejaculation  of  semen  may  be  caused 
by  stimulation  of  the  penis.  As  the  section  of  the  cord  has  left 
the  hinder  part  of  the  animal's  body  severed  from  the  brain, 
the  creature  is,  of  course,  unconscious  of  anything  happening 
in  all  the  parts  below  the  section,  of  whatever  nature.  If  the 
nervi  erigentes  (from  the  lower  part  of  the  spinal  cord)  be 
stimulated,  the  penis  is  erected ;  and  if  they  be  cut,  this  act  be- 
comes impossible,  either  refiexly  by  experiment  or  otherwise. 
Seminal  emissions,  it  is  well  known,  may  occur  during  sleep, 
and  may  be  associated,  either  as  result  or  cause,  with  voluptu- 
ous dreams.  Putting  all  these  facts  together,  it  seems  reason- 
able to  conclude  that  the  lower  part  of  the  sx)inal  cord  contains 
the  nervous  machinery  requisite  to  initiate  those  influences  (im- 
pulses) which,  passing  along  the  nerves  to  the  generative  or- 
gans, excite  and  regulate  the  processes  which  take  place  in 
them.  In  these,  vascular  changes,  as  we  have  seen,  always 
play  a  prominent  part. 

Usually  we  can  recognize  some  afferent  influence,  either 
from  the  brain  (psychical),  from  the  surface — at  all  events 
from  without  that  part  of  the  nervous  system  (center)  which 
functions  directly  in  the  various  sexual  processes.  It  is  com- 
mon to  speak  of  a  number  of  sexual  centers — as  the  erection 


THi!   DEVELOPMENT  OF  THE   UROGENITAL  SYSTEM.       125 

center,  the  ejaeulatory  center,  etc. — but  we  much  doubt  whether 
there  is  such  sharp  division  of  physiological  labor  as  these 
terms  imply,  and  they  are  liable  to  lead  to  misconception ;  ac- 
cordingly, in  the  present  state  of  our  knowledge,  we  prefer  to 
speak  of  the  sexual  center,  using  even  that  term  in  a  somewhat 
broad  sense. 

The  effects  of  stimulation  of  the  sexual  organs  are  not  con- 
fined to  the  parts  themselves,  but  the  ingoing  impulses  set  up 
radiating  outgoing  ones,  which  affect  widely  remote  areas  of 
the  body,  as  is  evident,  especially  in  the  vascular  changes ;  the 
central  current  of  nerve  influence  breaks  up  into  many  streams 
as  a  result  of  the  rapid  and  extensive  rise  of  the  outflowing 
current,  which  breaks  over  ordinary  barriers,  and  takes  paths 
which  are  not  properly  its  own.  Bearing  this  fact  in  mind, 
the  chemical  composition  of  semen,  so  rich  in  proteid  and  other 
material  valuable  from  a  nutritive  point  of  view,  and  consid- 
ering how  the  sexual  appetites  may  engross  the  mind,  it  is  not 
difficult  to  understand  that  nothing  so  quickly  disorganizes  the 
whole  man,  physical,  mental,  and  moral,  as  sexual  excesses, 
whether  by  the  use  of  the  organs  in  a  natural  way,  or  from 
masturbation. 

Nature  has  protected  the  lower  animals  by  the  strong  bar- 
rier of  instinct,  so  that  habitual  sexual  excess  is  with  them  an 
impossibility,  since  the  females  do  not  permit  of  the  approaches 
of  the  male  except  during  the  rutting  period,  which  occurs  only 
at  stated,  comparatively  distant  periods  in  most  of  the  higher 
mammals.  When  man  keeps  his  sexual  functions  in  subjection 
to  his  higher  nature,  they  likewise  tend  to  advance  his  whole 
development. 

Summary. — Certain  changes,  commencing  with  the  ripening 
of  ova,  followed  by  their  discharge  and  conveyance  into  the 
uterus,  accompanied  by  simultaneous  and  subsequent  modifica- 
tions of  the  uterine  mucous  membrane,  constitute,  when  preg- 
nancy occurs,  an  unbroken  chain  of  biological  events,  though 
usually  described  separately  for  the  sake  of  convenience. 
When  impregnation  does  not  result,  there  is  a  retrogression  in 
the  uterus  (menstruation)  and  a  return  to  general  quiescence 
in  all  the  reproductive  organs. 

Parturition  is  to  be  regarded  as  the  climax  of  a  variety  of 
rhythmic  occurrences  which  have  been  gradually  gathering 
head  for  a  long  period.  The  changes  which  take  place  in  the 
placenta  of  a  degenerative  character  fit  it  for  being  cast  off,  and 
may  render  this  structure  to  some  extent  a  foreign  b(Kly  })(ifove 


120  ANIMAL   PHYSIOLOGY. 

it  and  the  foetus  are  finally  expelled,  so  that  these  changes  may 
constitute  one  of  a  number  of  exciting  causes  of  the  increased 
uterine  action  of  parturition.  But  it  is  important  to  regard  the 
whole  of  the  occurrences  of  pregnancy  as  a  connected  series  of 
processes  co-ordinated  by  the  central  nervous  system  so  as  to 
accomplish  one  great  end,  the  development  of  a  new  individual. 

The  nutrition  of  the  ovum  in  its  earliest  stages  is  effected  by 
means  in  harmony  with  its  nature  as  an  amoeboid  organism ; 
nutrition  by  the  cells  of  blood-vessels  is  similar,  while  that  by 
villi  may  be  compared  to  what  takes  place  through  the  agency 
of  similar  structures  in  the  alimentary  canal  of  the  adult  mam- 
mal. 

The  circulation  of  the  foetus  puts  it  on  a  par  physiologically 
with  the  lower  vertebrates.  Before  birth  there  is  a  gradual 
though  somewhat  rapid  preparation,  resulting  in  changes 
which  speedily  culminate  after  birth  on  the  establishment  of 
the  permanent  condition  of  the  circulation  of  extra-uterine  life. 

The  blood  of  the  foetus  (as  in  the  adult)  is  the  great  store- 
house of  nutriment  and  the  common  receptacle  of  all  waste 
products ;  these  latter  are  in  the  main  transferred  to  the  moth- 
er's blood  indirectly  in  the  placenta ;  in  a  similar  way  nutri- 
ment is  imported  from  the  mother's  blood  to  that  of  the  foetus. 
The  placenta  takes  the  place  of  digestive,  respiratory,  and  ex- 
cretory organs. 

Coitus  is  essential  to  bring  the  male  and  female  elements 
together  in  the  higher  vertebrates.  The  erection  of  the  penis  is 
owing  to  vascular  changes  taking  place  in  an  organ  composed 
of  erectile  tissue ;  ejaculation  of  semen  is  the  result  of  the  peri- 
staltic action  of  the  various  parts  of  the  sexual  tract,  aided  by 
rhythmical  action  of  certain  striped  muscles.  The  spermatozoa, 
which  are  unicellular,  flagellated  (ciliated)  cells,  make  up  the  es- 
sential part  of  semen ;  though  the  latter  is  complicated  by  the 
addition  of  the  secretions  of  several  glands  in  connection  with 
the  seminal  tract.  Though  competent  by  their  own  movements 
of  reaching  the  ovum  in  the  oviduct,  it  is  probable  that  the 
uterus  and  oviduct  experience  peristaltic  actions  in  a  direction 
toward  the  ovary,  at  least  in  a  number  of  mammals. 

The  lower  part  of  the  spinal  cord  is  the  seat  in  the  higher 
mammals  of  a  sexual  center  or  collection  of  cells  that  receives 
afferent  impulses  and  sends  out  efferent  impulses  to  the  sexual 
organs.  This,  like  all  the  lower  centers,  is  under  the  control  of 
the  higher  centers  in  the  brain,  so  that  its  action  may  be  either 
initiated  or  inhibited  by  the  cerebrum. 


ORGANIC   EVOLUTION  RECONSIDERED.  127 


ORGANIC  EVOLUTION  RECONSIDERED. 

The  study  of  reproduction  has  prepared  the  student  for  the 
comprehension  of  certain  views  of  the  origin  of  the  forms  of 
life  which  could  not  be  as  profitably  considered  before. 

While  the  great  majority  of  biologists  are  convinced  that 
there  has  been  a  gradual  evolution  of  more  complex  organisms 
from  simpler  ones,  and  while  most  believe  that  Darwin's  the- 
ory furnishes  some  of  the  elements  of  a  solution  of  the  problem 
as  to  how  this  has  occurred,  many  still  feel  that  the  whole  ex- 
planation was  not  furnished  by  that  great  naturalist. 

Accordingly,  we  shall  notice  very  briefly  a  few  of  the  more 
important  contributions  to  this  subject  since  Darwin's  views 
were  published. 

In  America,  under  the  influence  of  the  writings  of  Cope  and 
Hyatt,  a  school  of  evolutionists  has  been  formed,  holding  doc- 
trines that  constitute  a  modification  of  those  announced  in 
cruder  form  by  Lamarck,  hence  termed  neo-Lamarckianism. 
These  authors  have  imported  consciousness  into  the  list  of 
factors  of  organic  evolution  and  given  it  a  prominent  place. 
They  regard  consciousness  as  a  fundamental  property  of  proto- 
plasm ;  it  determines  effort  and  the  direction  that  activity  shall 
take  :  thus  hunger  leads  to  migration,  and  brings  the  creature 
under  a  new  set  of  conditions  which  influence  its  nature.  A 
certain  proportion  of  the  changes  an  animal  undergoes  are  at- 
tributed to  the  direct  influence  of  surrounding  conditions  (en- 
vironment), but  the  larger  number  are  owing  to  efforts  involv- 
ing the  greater  use  of  some  parts  than  others,  which  tends  to 
Vjecorae  habitual.  This  is  the  explanation  neo-Lamarckianism 
offers  for  the  origin  of  variations.  It  is  assumed  that  the  re- 
sults of  use  or  disuse  of  parts  is  inherited,  so  that  the  gain  or 
loss  is  not  transient  with  the  individual,  but  remains  with  the 
group. 

This  theory  also  refers  the  loss  or  preservation  of  certain 
structures  to  "  acceleration  "  or  "  retardation  "  of  growth ;  thus, 
if  the  growth  of  gills  were  greatly  and  progressively  retarded 
during  embryonic  life,  they  might  become  only  rudimentary, 
and  this  would  furnish  an  explanation  of  the  origin  of  rudiment- 
ary organs,  tliough  it  is  clear  that  use  and  effort  could  not  di- 
rectly explain  such  acceleration  or  retardation.  It  is  further  a 
fact,  which  this  theory  does  not  explain,  that  all  variations  of 
structure  produced  by  use  are  not  inherited. 


128  ANIMAL   PHYSIOLOGY. 

Weismann,  in  fact,  denies  that  peculiarities  acquired  dur- 
ing the  lifetime  of  the  adult  are  passed  dn  to  offspring.  This 
writer  believes  that  we  must  seek  in  Amoeba,  as  the  ancestral 
representative  of  the  ovum,  for  the  clew  to  the  laws  of  heredity. 
The  Amoeba  must  divide  or  cease  to  exist  as  a  group  form — 
hence  the  segmentation  of  the  ovum ;  this  is  but  the  inherited 
tendency  to  divide.  What  the  individual  becomes  is  determined 
entirely  by  the  ovum,  the  v^hole  of  which  does  not  develop  into 
the  new  being,  but  a  part  is  laid  aside  in  reserve  as  the  future 
ovum.  Any  variations  that  show  themselves  in  future  indi- 
viduals are  such  as  arise  from  the  variations  of  the  ovum  itself. 

According  to  this  writer,  it  is  as  natural  for  the  offspring  to 
resemble  the  parent  (heredity)  in  the  higher  groups  of  animals 
as  that  one  Amoeba  should  resemble  another,  and  for  the  same 
reason. 

Weismann  has  also  attempted  to  explain  the  necessity  and 
the  significance  of  the  extrusion  of  polar  globules.  The  first 
polar  globule  is  expelled  from  all  ova,  even  those  that  can  de- 
velop independent  of  a  male  cell  (parthenogenetic).  This  rep- 
resents that  part  of  the  original  ovum  which  determines  its 
peculiarities  of  form,  etc.  (ovogenetic  idioplasm) ;  while  the 
second  polar  globule  is  one  half  of  the  nucleus  of  the  mature 
ovum  ready  to  enter  upon  development,  if  fertilized.  When 
the  latter  takes  place,  it  is  joined  by  the  corresponding  nuclear 
substance  of  the  male  cell  to  form  the  segmentation  nucleas. 
It  is  this  substance  (germ-plasma)  which  determines  exactly 
what  line  of  development,  to  the  minutest  details,  the  ovum 
shall  follow.  In  the  course  of  time  the  nucleus  would  thus 
come  to  represent  many  generations  of  united  plasmas.  There 
must  be  a  limit  to  this,  from  the  physical  necessities  of  the  case ; 
hence  the  expulsion  of  a  second  polar  globule,  which  also  is  a 
provision  against  parthenogenesis,  for  in  some  cases  the  plasma 
of  the  nucleus  has  the  power,  without  the  accession  of  any 
male  plasma,  to  segment  and  develop  the  mature  animal.  But 
in  any  case  there  is  a  great  advantage  in  the  union  of  the  two 
plasmas  with  their  diverse  experiences ;  hence  sexual  rejjro- 
duction,  though  the  most  costly  apparently,  is  in  reality  the 
most  economical  for  Nature  in  the  end,  for  higher  results  are 
reached,  and  it  seems,  in  fact,  that  this  lies  at  the  very  foun- 
dation of  organic  progress. 

The  theory  of  Brooks  may  be  regarded  as  eclectic,  being  a 
combination  of  that  of  Weismann  and  Darwin  more  particu- 
larly, with  entirely  new  additions  by  himself. 


ORGANIC  EVOLUTION  RECONSIDERED.  129 

Darwin  believed  that  every  part  of  the  body  gave  off  "  gem- 
mules/'  or  very  minute  bodies,  which  were  collected  into  the 
ovum,  and  thus  the  ovum  came  to  be  a  sort  of  abstract  of  the 
whole  body — hence  the  resemblance  of  offspring  to  parents, 
since  the  development  of  the  ovum  was  but  that  of  the  gem- 
mules.  Some  of  the  gemmules  might  remain  latent  for  genera- 
tions, and  then  develop ;  hence  that  resemblance  often  seen  to 
ancestors  more  remote  than  the  parents  (reversion).  This  is  a 
very  brief  account  of  Darwin's  hypothesis  of  pangenesis. 

This  writer,  however,  never  accounted  for  variations.  He 
spoke  of  variations  as  "  spontaneous,"  meaning,  not  that  they 
were  supernatural,  but  that  it  was  not  possible  to  assign  them 
to  a  definite  cause.  To  account  for  variation  has  naturally  been 
the  aim  of  later  writers.  How  neo-Lamarckianism  does  this 
has  been  already  considered.  We  now  give  the  views  of  Brooks 
on  this  and  other  points  in  connection  with  organic  evolution. 

This  thinker,  like  Weismann,  looks  to  the  fertilized  ovum 
for  an  explanation  of  the  main  facts ;  but  Brooks  refers  the 
origin  of  variations  to  the  influence  of  the  male  cell.  This  is, 
of  course,  a  pure  hypothesis,  but  it  is  in  harmony  with  many 
facts  which  were  in  need  of  explanation.  It  had  been  noticed 
by  Darwin  that  variations  of  all  kinds  were  most  apt  to  arise 
upon  alteration  in  the  conditions  under  which  an  animal 
lived.  Brooks  also  believes  in  gemmules,  but  does  not  think 
they  are  given  off  from  all  parts  equally  or  at  all  times,  but 
that  they  are  derived  from  those  parts  most  affected  by  the 
change  of  surroundings ;  and  since  this  would  influence  parts 
much  when  for  the  worse,  variation  would  coincide  with  suf- 
fering or  need ;  hence  those  very  parts  would  vary,  and  so  pre- 
pare for  adaptation,  just  when  this  was  most  called  for  by  the 
nature  of  the  case.  But  the  male  sexual  element,  it  has  been 
shovrn,  is  more  liable  to  variation  than  the  ovum ;  hence  the  ex- 
planation of  what  Brooks  believes  to  be  a  fact,  that  it  is  the 
sperm-cell  that  generally  is  responsible  for  variation,  since  it 
chiefly  collects  the  gemmules. 

The  author  of  this  theory  points  to  parthenogenetic  forms 
being  less  variable,  as  evidence  of  the  truth  of  his  view.  To 
introduce  a  male  cell  is  to  impart  vast  numbers  of  new  gem- 
mules, and  thus  induce  variability.  This  hypothesis  would  ex- 
plain why  the  female  represents  what  is  most  fundamental  and 
ancient  in  the  history  of  psychological  development,  and  the 
male  what  is  associated  with  enterjjriso — in  a  word,  the  female 
preserves,  the  male  originates,  in  the  widest  sense. 
9 


230  ANIMAL  PHYSIOLOGY. 

Vines  lias  stated  that  the  equivalent  of  parthenogenesis 
takes  place  in  the  male  cell  in  plants.  Though  this  may  be  an 
objection  to  the  universality  of  application  of  Brooks's  theory, 
it  does  not  seem  to  us  to  be  fatal  to  it  as  a  whole. 

As  has  been  pointed  out,  in  a  previous  chapter,  Darwin  held 
that  the  differences  that  caused  ultimately  the  formation  of 
new  groups  of  living  forms  were  the  result  of  extremely  slow 
accumulation  of  variations,  at  first  very  minute.  He  every- 
where insists  upon  this.  But,  unquestionably,  it  is  just  here 
that  the  greatest  difficulty  is  to  be  encountered  in  the  Darwin- 
ian account  of  evolution.  The  chances  against  the  loss  of  the 
variation  by  breeding  with  forms  that  did  not  possess  it  seem 
to  be  numerous,  hence  various  theories  have  been  proposed  to 
lessen  the  difficulty. 

Mivart  introduced  the  doctrine  of  extraordinary  births,  be- 
lieving that  variations  were  often  sudden  and  pronounced. 
That  they  were  so  occasionally  Darwin  himself  admitted ;  but 
he  considered  a  theory  like  that  of  Mivart  as  a  surrender,  a 
resort  to  an  explanation  that  verged  in  its  character  on  the 
introduction  of  the  supernatural  itself. 

A  view  that  has  attracted  much  attention  and  caused  a 
great  deal  of  controversy,  is  that  of  Romanes,  which  was  intro- 
duced in  part  to  meet  the  difficulty  just  referred  to ;  and  to  lessen 
the  further  one  arising  from  the  infertility  of  species  with  one 
another,  as  compared  with  the  perfect  fertility  of  varieties.  It 
has  often  been  noticed  that,  though  the  difference  anatomically 
between  varieties  might  be  greater  than  between  species,  the 
above  law  as  to  fertility  still  held.  Such  a  fact  calls  for  ex- 
planation ;  hence  Romanes  has  proposed  his  theory  of  "  physi- 
ological selection"  (segregation,  isolation).  If  it  be  admitted 
that  some  change  may  take  place  in  the  sexual  organs  of  two 
forms  so  that  the  members  of  one  are  fertile  with  each  other 
while  those  of  the  other  are  not,  it  will  at  once  appear  that 
they  are  as  much  isolated  physiologically  as  if  separated  by  an 
ocean.  That  such  does  take  place  is  an  assumption  based  on 
the  great  tendency  in  the  reproductive  organs  to  change ;  and 
it  is  claimed  that,  if  this  assumption  be  granted,  that  the  main 
difficulty  of  Darwin's  theory  will  be  removed,  for  the  '"  swamp- 
ing "  action  of  intercrossing  forms  that  vary  slightly,  or  one  of 
them  not  at  all,  in  the  given  direction,  will  not  occur.  Romanes 
believes  that  forms  that  vary  are  fertile  inter  se,  but  not  with 
the  parent  forms,  which  would  meet  the  case  fairly  well.  Cer- 
tain it  is  that  species  are  not  generally  fertile  with  one  an- 


ORGANIC  EVOLUTION  RECONSIDERED.  131 

other  while  varieties  are  so  invariably ;  and  it  is  this  that,  in 
the  opinion  of  Romanes  and  many  others,  has  never  been  ade- 
quately explained. 

Admitting  that  the  theories  of  Romanes,  Brooks,  and  Weis- 
mann  have  advanced  us  on  the  way  to  more  complete  views  of 
the  mode  of  origin  of  the  forms  of  the  organic  world,  it  must 
still  be  felt  that  all  theories  yet  propounded  fall  short  of  being 
entirely  satisfactory.  It  seems  to  us  unfortunate  that  the  sub- 
ject has  not  received  more  attention  from  physiologists,  as 
without  doubt  the  final  solution  must  come  through  that  sci- 
ence which  deals  with  the  properties  rather  than  the  forms 
of  protoplasm ;  or,  in  other  words,  the  fundamental  principles 
underlying  organic  evolution  are  physiological.  But,  in  the 
unraveling  of  a  subject  of  such  extreme  complexity,  all  sci- 
ences must  probably  contribute  their  quota  to  make  up  the 
truth,  as  many  rays  of  different  colors  compounded  form  white 
light.  As  with  other  theories  of  the  inductive  sciences,  none 
can  be  more  than  temporary ;  there  must  be  constant  modifi- 
cation to  meet  increasing  knowledge.  Conscious  that  any 
views  we  ourselves  advance  must  sooner  or  later  be  modified 
as  all  others,  even  if  acceptable  now,  we  venture  to  lay  before 
the  reader  the  opinions  we  have  formed  upon  this  subject  as 
the  result  of  considerable  thought. 

All  vital  phenomena  may  be  regarded  as  the  resultant  of 
the  action  of  external  conditions  and  internal  tendencies.  Amid 
the  constant  change  which  life  involves  we  recognize  two 
things :  the  tendency  to  retain  old  modes  of  behavior,  and  the 
tendency  to  modification  or  variation.  Since  those  impulses 
originally  bestowed  on  matter  when  it  became  living,  must,  in 
order  to  prevail  against  the  forces  from  without,  which  tend 
to  destroy  it,  have  considerable  potency,  the  tendency  to  modi- 
fication is  naturally  and  necessarily  less  than  to  permanence  of 
form  and  function. 

From  these  principles  it  follows  that  when  an  Amoeba  or 
kindred  organism  divides  after  a  longer  or  shorter  period,  it  is 
not  in  reality  the  same  in  all  respects  as  when  its  existence 
began,  thougli  we  may  be  quite  unable  to  detect  the  changes ; 
and  when  two  infusorians  con  jugate,  the  one  brings  to  the  other 
protophism  flifTerent  in  molecular  behavior,  of  necessity,  from 
having  had  diffr-rent  experiences.  We  attach  great  importance 
to  these  principles,  as  they  seem  to  us  to  lie  at  the  root  of  the 
whole  matter.     What  has  been  said  of  these  lower  but  inde- 


]^32  ANIMAL  PHYSIOLOGY. 

pendent  forms  of  life  applies  to  the  higher.  All  organisms  are 
made  up  of  cells  or  aggregations  of  cells  and  their  products. 
For  the  present  we  may  disregard  the  latter.  When  a  muscle- 
cell  by  division  gives  rise  to  a  new  cell,  the  latter  is  not  identi- 
cally the  same  in  every  particular  as  the  parent  cell  was  origi- 
nally. It  is  what  its  parent  has  become  by  virtue  of  those 
experiences  it  has  had  as  a  muscle-cell  per  se,  and  as  a  member 
of  a  populous  biological  community,  of  the  complexities  of 
which  we  can  scarcely  conceive. 

Now,  as  a  body  at  rest  may  remain  so,  or  may  move  in  a 
certain  direction  according  as  the  forces  acting  upon  it  exactly 
counterbalance  one  another,  or  produce  a  resultant  effect  in 
the  direction  in  which  the  body  moves,  so  in  the  case  of  he- 
redity, whether  a  certain  quality  in  the  parent  appears  in  the 
offspring,  depends  on  whether  this  quality  is  neutralized,  aug- 
mented, or  otherwise  modified  by  any  corresponding  quality  in 
the  other  parent,  or  by  some  opposite  quality,  taken  in  connec- 
tion with  the  direct  influence  of  the  environment  during  devel- 
opment. 

This  assumption  explains  among  other  things  why  acquired 
peculiarities  (the  results  of  accident,  habit,  etc.)  may  or  may 
not  be  inherited. 

These  are  not  usually  inherited  because,  as  is  to  be  expect- 
ed, those  forces  of  the  organism  which  have  been  gathering 
head  for  ages  are  naturally  not  easily  turned  aside.  Again,  we 
urge,  heredity  must  be  more  pronounced  than  variation. 

The  ovum  and  sperm-cell,  like  all  other  cells  of  the  body, 
are  microcosms  representing  the  whole  to  a  certain  extent  in 
themselves — that  is  to  say,  cell  A  is  what  it  is  by  reason  of  what 
all  the  other  millions  of  its  fellows  in  the  biological  republic 
are ;  so  that  it  is  possible  to  understand  why  sexual  cells  repre- 
sent, embody,  and  repeat  the  whole  biological  story,  though  it 
is  not  yet  possible  to  indicate  exactly  how  they  more  than 
others  have  this  power.  This  falls  under  the  laws  of  speciali- 
zation and  the  physiological  division  of  labor ;  but  along  what 
paths  they  have  reached  this  we  can  not  determine. 

Strong  evidence  is  furnished  for  the  above  views  by  the  his- 
tory of  disease.  Scar-tissue,  for  example,  continues  to  repro- 
duce itself  as  such ;  like  produces  like,  though  in  this  instance 
the  like  is  in  the  first  instance  a  departure  from  the  normal. 
Gout  is  well  known  to  be  a  hereditary  disease ;  not  only  so,  but 
it  arises  in  the  offspring  at  about  the  same  age  as  in  the  parent, 
which  is  equivalent  to  saying  that  in  the  rhythmical  life  of 


ORGANIC  EVOLUTION  RECONSIDERED.  133 

certain  cells  a  period  is  reached  when  they  display  the  behav- 
ior, physiologically,  of  their  parents.  Yet  gout  is  a  disease 
that  can  be  traced  to  peculiar  habits  of  living  and  may  be 
eventually  escaped  by  radical  changes  in  this  respect — that  is 
to  say,  the  behavior  of  the  cells  leading  to  gout  can  be  induced 
and  can  be  altered ;  gout  is  hereditary,  yet  eradicable. 

Just  as  gout  may  be  set  up  by  formation  of  certain  modes 
of  action  of  the  cells  of  the  body,  so  may  a  mode  of  behavior,  in 
the  nervous  system,  for  example,  become  organized  or  fixed,  be- 
come a  habit,  and  so  be  transmitted  to  offspring.  It  will  pass 
to  the  descendants  or  not  according  to  the  principles  already 
noticed.  If  so  fixed  in  the  individual  in  which  it  arises  as  to 
predominate  over  more  ancient  methods  of  cell  behavior,  and 
not  neutralized  by  the  strength  of  the  normal  physiological  ac- 
tion of  the  corresponding  parts  in  the  other  parent,  it  will  reap- 
pear. We  can  never  determine  whether  this  is  so  or  not  before- 
hand ;  hence  the  fact  that  it  is  impossible,  especially  in  the  case 
of  man,  whose  vital  processes  are  so  modified  by  his  psychic 
life,  to  predict  whether  acquired  variations  shall  become  heredi- 
tary ;  hence  also  the  irregularity  which  characterizes  heredity 
in  such  cases ;  they  may  reappear  in  offspring  or  they  may  not. 
In  viewing  heredity  and  modification  it  is  impossible  to  get  a 
true  insight  into  the  matter  without  taking  into  the  account 
both  original  natural  tendencies  of  living  matter  and  the  influ- 
ence of  environment.  Wg  only  know  of  vital  manifestations 
in  some  environment ;  and,  so  far  as  our  experience  goes,  life  is 
impossible  apart  from  the  influence  of  surroundings.  With 
these  general  principles  to  guide  us,  we  shall  attempt  a  brief 
examination  of  the  leading  theories  of  organic  evolution. 

First  of  all,  Spencer  seems  to  be  correct  in  regarding  evolu- 
tion as  universal,  and  organic  evolution  but  one  part  of  a 
whole.  No  one  who  looks  at  the  facts  presented  in  every  field 
of  nature  can  doubt  that  struggle  (opposition,  action  and  reac- 
tion) is  universal,  and  that  in  the  organic  world  the  fittest  to  a 
given  environment  survives.  But  Darwin  has  probably  fixed 
his  attention  too  closely  on  this  principle  and  attempted  to  ex- 
plain too  much  by  it,  as  well  as  failed  to  see  that  there  are 
other  deeper  facts  underlying  it.  Variation,  which  this  author 
scarcely  attempted  to  explain,  seems  to  us  to  be  the  natural  re- 
sult of  the  very  conditions  under  which  living  things  have  an 
existence.  Stable  equilibriiim  is  an  idea  incompatible  with  our 
fundamental  conceptions  of  life.  Altered  function  implies  al- 
tered molecular  action,  which  sometimes  leads  to  appreciable 


134 


ANIMAL  PHYSIOLOGY. 


structural  change.  From  our  conceptions  of  the  nature  of  liv- 
ing matter,  it  naturally  follows  that  variation  should  be  great- 
est, as  has  been  observed,  under  the  greatest  alteration  in  the 
surroundings. 

We  are  but  very  imperfectly  acquainted  as  yet  with  the 
conditions  under  which  life  existed  in  the  earlier  epochs  of  the 
earth's  history.  Of  late,  deep-sea  soundings  and  arctic  explo- 
rations have  brought  surprising  facts  to  light,  showing  that 
living  matter  can  exist  under  a  greater  variety  of  conditions 
than  was  previously  supposed.  Thus  it  turns  out  that  light  is 
not  an  essential  for  life  everywhere.  We  think  these  recent 
revelations  of  unexpected  facts  should  make  us  cautious  in  as- 
suming that  life  always  manifested  itself  under  conditions 
closely  similar  to  those  we  know.  Variation  may  at  one  period 
have  been  more  sudden  and  marked  than  Darwin  supposes; 
and  there  does  seem  to  be  room  for  such  a  conception  as  the 
"  extraordinary  births  "  of  Mivart  implies ;  though  we  would  not 
have  it  understood  that  we  think  Darwin's  view  of  slow  modi- 
fication inadequate  to  produce  a  new  species ;  we  simply  vent- 
ure to  think  that  he  was  not  justified  in  insisting  so  strongly 
that  this  was  the  only  method  of  Nature ;  or,  to  put  it  more 
justly  for  the  great  author  of  the  "  Origin  of  Species,"  with  the 
facts  that  have  accumulated  since  his  time  he  would  scarcely 
be  warranted  in  maintaining  so  rigidily  his  conviction  that 
new  forms  arose  almost  exclusively  by  the  slow  process  he  has 
so  ably  described. 

As  there  must  be  all  degrees  in  consciousness,  we  do  not 
deny  that  it  may  be  logical  to  assume  some  dim  spark  of  this 
quality  in  all  protoplasm,  as  Cope  insists ;  and  that  it  plays  a 
part  in  determining  action  and  growth  there  seems  to  be  no 
doubt.  But  is  it  not  more  philosophical  to  regard  conscious- 
ness and  all  allied  qualities  as  correlatives,  and  underlaid  by  a 
molecular  constitution  with  which  it  is  associated  as  other  qual- 
ities ?    It  is  unduly  exalted  in  the  neo-Lamarckian  philosophy. 

We  must  allow  a  great  deal  to  use  and  effort,  doubtless,  and 
they  explain  the  origin  of  variations  up  to  a  certain  point,  but 
the  solution  is  only  partial.  Variations  must  arise  as  we  have 
attempted  to  explain,  and  use  and  disuse  are  only  two  of  the 
factors  amid  many.  Correlated  growth,  or  the  changes  in  one 
part  induced  by  changes  in  another,  is  a  principle  which,  though 
recognized  by  Darwin,  Cope,  and  others,  has  not,  we  think,  re- 
ceived the  attention  it  deserves.  To  the  mind  of  the  physiolo- 
gist, all  changes  must  be  correlated  with  others. 


THE   CHEMICAL  CONSTITUTION  OF  THE  ANIMAL  BODY.  135 

This  principle  has  played  a  great  part  in  the  development  of 
man,  as  we  shall  show  later. 

Weismann's  theories  have  called  attention  to  the  ovum  in  a 
new  and  valuable  way,  though  he  seems  to  have  given  too  ex- 
clusive attention  to  the  nucleus  {gevni-plasma)  in  itself  and 
out  of  relation  to  the  influence  of  the  countless  cells  that 
make  up  the  body  and  must  be  constantly  determining  modi- 
fications of  the  generative  organs  and  the  sexual  cells  them- 
selves ;  so  that  Brooks's  explanation,  by  adding  a  new  factor, 
or,  at  least,  presenting  a  new  aspect  of  the  case,  was  called 
for  and  seems  to  be  warranted  on  the  general  principle  that 
advance  in  protoplasmic  life  is  dependent  on  new  experiences, 
and  that  the  male  cell  represents  a  little  world  of  the  concen- 
trated experiences  gathered  during  the  lifetime  of  the  or- 
ganism that  produced  it.  But  we  must  consider  the  whole 
doctrine  of  gemmules  as  a  crude  and  entirely  unnecessary 
hypothesis. 

In  what  sense  has  the  line  that  evolution  has  taken  been 
predetermined  ?  In  the  sense  that  all  things  in  the  universe 
are  unstable,  are  undergoing  change,  leading  to  new  forms  and 
qualities  of  such  a  character  that  they  result  in  a  gradual  prog- 
ress toward  what  our  minds  can  not  but  consider  higher  mani- 
festations of  being. 

The  secondary  methods  according  to  which  this  takes  place 
constitute  the  laws  of  nature,  and  as  we  learn  from  the  progress 
of  science  are  very  numerous.  The  unity  of  nature  is  a  real- 
ity toward  which  our  conceptions  are  constantly  leading  us. 
Evolution  is  a  necessity  of  living  matter  (indeed,  all  matter)  as 
we  view  it. 


THE  CHEMICAL  CONSTITUTION  OF  THE  ANIMAL  BODY. 

One  visiting  the  ruins  of  a  vast  and  elaborate  building, 
which  had  been  thoroughly  pulled  to  pieces,  would  get  an 
amount  of  information  relative  to  the  original  structure  and 
uses  of  the  various  parts  of  the  edifice  largely  in  proportion  to 
his  familiarity  with  architecture  and  the  various  trades  which 
make  that  art  a  practical  success.  The  study  of  the  ch(!mistry 
of  the  animal  body  is  illustrated  by  such  a  case.  Any  attempt 
to  determine  the  exact  chemical  composition  of  living  inatter 
mu.st  result  in  its  destruction;  and  the  amcmnt  of  information 
conveyed  by  the  examination  of  the  chemical  ruins,  so  to  speak. 


136 


ANIMAL  PHYSIOLOGY. 


will  depend  a  great  deal  on  tlie  knowledge  already  possessed  of 
ch.emical  and  vital  processes. 

It  is  in  all  probability  true  tbat  the  nature  of  any  vital  pro- 
cess is  at  all  events  closely  bound  up  with  the  chemical  changes 
involved  ;  but  we  must  not  go  too  far  in  this  direction.  We  are 
not  yet  prepared  to  say  that  life  is  only  the  manifestation  of 
certain  chemical  and  physical  processes,  meaning  thereby  such 
chemistry  and  physics  as  are  known  to  us ;  nor  are  we  prepared 
to  go  the  length  of  those  who  regard  life  as  but  the  equivalent 
of  some  other  force  or  forces ;  as  electricity  may  be  considered 
as  the  transformed  representative  of  so  much  heat  and  vice 
versa.  It  may  be  so,  but  we  do  not  consider  that  this  view  is 
warranted  in  the  present  state  of  our  knowledge. 

On  the  other  hand,  vital  phenomena,  when  our  investiga- 
tions are  pushed  far  enough,  always  seem  to  be  closely  asso- 
ciated with  chemical  action ;  hence  the  importance  to  the  stu- 
dent of  physiology  of  a  sound  knowledge  of  chemical  princi- 
ples. We  think  the  most  satisfactory  method  of  studying  the 
functions  of  an  organ  will  be  found  to  be  that  which  takes  into 
consideration  the  totality  of  the  operations  of  which  it  is  the 
seat,  together  with  its  structure  and  chemical  composition; 
hence  we  shall  treat  chemical  details  in  the  chapters  devoted  to 
special  physiology,  and  here  give  only  such  an  outline  as  will 
bring  before  the  view  the  chemical  composition  of  the  body  in 
its  main  outlines ;  and  even  many  of  these  will  gather  a  signifi- 
cance, as  the  study  of  physiology  progresses,  that  they  can  not 
possibly  have  at  the  present. 

Fewer  than  one  third  of  the  chemical  elements  enter  into 
the  composition  of  the  mammalian  body ;  in  fact,  the  great 
bulk  of  the  organism  is  composed  of  carbon,  hydrogen,  nitro- 
gen, and  oxygen;  sodium,  potassium,  magnesium,  calcium, 
sulphur,  phosphorus,  chlorine,  iron,  fluorine,  silicon,  though 
occurring  in  very  small  quantity,  seem  to  be  indispensable  to 
the  living  body ;  while  certain  others  are  evidently  only  pres- 
ent as  foreign  bodies  or  impurities  to  be  thrown  out  sooner 
or  later.  It  need  scarcely  be  said  that  the  elements  do  not 
occur  as  such  in  the  living  body,  but  in  combination  form- 
ing salts,  which  latter  are  usually  united  with  albuminous 
compounds.  As  previously  mentioned,  the  various  parts  which 
make  up  the  entire  body  of  an  animal  are  composed  of  living 
matter  in  very  different  degrees ;  hence  we  find  in  such  parts 
as  the  bones  abundance  of  salts,  relative  to  the  proportion  of 
proteid  matter ;  a  condition  demanded  by  that  rigidity  without 


THE  CHEMICAL  CONSTITUTION  OP  THE  ANIMAL  BODY.  I37 

whicli  an  internal  skeleton  would  be  useless,  a  defect  well  illus- 
trated by  that  disease  of  the  bones  known  as  rickets,  in  which 
the  lime-salts  are  insufficient.  It  is  manifest  that  there  may  be 
a  very  great  variety  of  classifications  of  the  compounds  found 
in  the  animal  body  according  as  we  regard  it  from  a  chemical, 
physical,  or  physiological  point  of  view,  or  combine  many 
aspects  in  one  whole.  The  latter  is,  of  course,  the  most  correct 
and  profitable  method,  and  as  such  is  impossible  at  this  stage 
of  the  student's  progress  ;  we  shall  simply  present  him  with  the 
following  outline,  which  will  be  found  both  simjjle  and  com- 
prehensive.* The  subject  of  Animal  Chemistry  will  be  found 
treated  in  detail  in  the  Appendix. 

CHEMICAL  CONSTITUTION  OF  THE  BODY. 

Such  food  as  supplies  energy  directly  must  contain  carbon 
compounds. 

Living  matter  or  protoplasm  always  contains  nitrogenous 
carbon  compounds. 

In  consequence,  C,  H,  O,  IST,  are  the  elements  found  in  great- 
est abundance  in  the  body. 

The  elements  S  and  P  are  associated  with  the  nitrogenous 
carbon  compounds ;  they  also  form  metallic  sulphates  and  phos- 
XJhates. 

CI  and  F  form  salts  with  the  alkaline  metals  Na,  K,  and  the 
earthy  metals  Ca  and  Mg. 

Fe  is  found  in  luemoglohin  and  its  derivatives. 

Protoplasm,  when  submitted  to  chemical  examination,  is 
killed.  It  is  then  found  to  consist  of  proteids,  fats,  carbohy- 
drates, salines,  and  extractives. 

It  is  probable  that  when  living  it  has  a  very  complex  mole> 
cule  consisting  of  C,  H,  O,  N,  S,  and  P  chiefly. 

PROXIMATE   PRINCIPLES. 

1    Or   anic        j  ^^^  ^'*^*'^^^°"^-  ]  Certain  crystalline  bodies. 

°  ■       I  ,-,.  TVT         -i.  S  Carbohydrates. 

(  (b)  Non-mtrogenous.  •)  xj^  ^ . 


„    ,  .1  Mineral  salts. 

2.  Inorganic.    ^.^ 


I  Water 

Salts. — In  general,  the  salts  of  sodium  are  more  characteris- 
tic of  animal  tissues  and  those  of  potassium  of  vegetable  tissues. 

*  Takf-ri  from  Iho  iiuthor's  "Outlines of  Lectures  on  Physiology,"  W.  Dry.sdalo 
&  Co.,  Moritr«;ul. 


138  ANIMAL  PHYSIOLOGY. 

N"a  CI  is  more  abundant  in  the  fluids  of  animals ;  K  and 
phosphates  more  abundant  in  the  tissues. 

Earthy  salts  are  most  abundant  in  the  harder  tissues. 

The  salts  are  probably  not  much,  if  at  all,  changed  in  their 
passage  through  the  body. 

In  some  cases  there  is  a  change  from  acid  to  neutral  or 
alkaline. 

The  salts  are  essential  to  preserve  the  balance  of  the  nutri- 
tive processes.    Their  absence  leads  to  disease,  e.  g.,  scurvy. 

GENERAL   CHARACTERISTICS   OF   PROTEIDS. 

They  are  the  chief  constituents  of  most  living  tissues,  in- 
cluding blood  and  lymph. 

The  molecule  consists  of  a  great  number  of  atoms  (complex 
constitution),  and  is  formed  of  the  elements  C,  H,  'N,  O,  S,  and  P. 

All  proteids  are  amorphous. 

All  are  non-diffusible,  the  peptones  excepted. 

They  are  soluble  in  strong  acids  and  alkalies,  with  change 
of  properties  or  constitution. 

In  general,  they  are  coagulated  by  alcohol,  ether,  and  heating. 

Coagulated  proteids  are  soluble  only  in  strong  acids  and 
alkalies. 

Classification  and  Distinguishing  Characters  of  Proteids. 

1.  Native  albumins :  Serum  albumin ;  Qgg  albumin ;  soluble 
in  water. 

2.  Derived  albumins  {albuminates)  :  Acid  and  alkali  albu- 
min ;  casein ;  soluble  in  dilute  acids  and  alkalies,  insoluble  in 
water.    ISTot  precipitated  by  boiling. 

3.  Olohidins :  Globulin  (globin)  ;  paraglobulin  ;  myosin ; 
fibrinogen.  Soluble  in  dilute  saline  solutions,  and  precipitated 
by  stronger  saline  solutions. 

4.  Peptones :  Soluble  in  water ;  diffusible  through  animal 
membranes ;  not  precipitated  by  acids,  alkalies,  or  heat.  De- 
rived from  the  digestion  (peptic,  pancreatic)  of  all  proteids. 

5.  Fibrin:  Insoluble  in  water  and  dilute  saline  solutions. 
Soluble,  but  not  readily,  in  strong  saline  solutions  and  in  dilute 
acids  and  alkalies. 

CERTAIN  NON-CRYSTALLINE   BODIES. 

The  following  bodies  are  allied  to  proteids,  but  are  not  the 
equivalents  of  the  latter  in  the  food. 


THE   CHEMICAL  CONSTITUTION   OF   THE    ANIMAL   BODY.  I39 

They  are  all  composed  of  C,  H,  IST,  O.  Chondrin,  gelatin, 
ceratin  have,  in  addition,  S. 

Cliondrin :  The  organic  basis  of  cartilage.  Its  solutions 
set  into  a  firm  jelly  on  cooling. 

Gelatin  :  The  organic  basis  of  bone,  teeth,  tendon,  etc.  Its 
solutions  set  (glue)  on  cooling. 

Elastin  :  The  basis  of  elastic  tissue.  Its  solutions  do  not  set 
jelly-like  (gelatinize). 

Mucin  :  From  the  secretion  of  mucous  membranes ;  precipi- 
tated by  acetic  acid,  and  insoluble  in  excess. 

Keratin  :  Derived  from  hair,  nails,  epidermis,  horn,  feathers. 
Highly  insoluble. 

Xuclein :  Derived  from  the  nuclei  of  cells.  Not  digested 
by  pepsin ;  contains  P  but  no  S. 

THE   FATS. 

The  fats  are  hydrocarbons ;  are  less  oxidized  than  the  carbo- 
hydrates; are  inflammable;  possess  latent  energy  in  a  high 
degree. 

Chemically,  the  neutral  fats  are  glycerides  or  ethers  of  the 
fatty  acids,  i.  e.,  the  acid  radicles  of  the  fatty  acids  of  the  oleic 
and  acetic  series  replace  the  exchangeable  atoms  of  H  in  the 
triatomic  alcohol  glycerine,  e.  g. : 

Glycerine.  Palmitic  acid.  Glycerine  tripalmitate  or  palmitin. 

I  OH      HO.OC.C.5H3,  ( O.CO.CuHa. 

C3H5  '  OH  +  HO.OC.CsHs,  =  C3H5  ]  O.CO.CsHa,  -I-  3H,0 
)  OH      HO.OC.C,5H3,  (  O.CO.CisHs, 

A  soajy  is  formed  by  the  action  of  caustic  alkalies  on 
fats,  e.  g. : 

Tripalmitin.  Potassium  palmitate. 

The  soap  may  be  decomposed  by  a  strong  acid  into  a  fatty 
acid  and  glycerine,  e.  g. : 

C,5H3,.CO,K  +  HCl  =  CsHai.CO.H  +  KCl. 

Potassium  palmitate.  Palmitic  acid. 

The/a/.v  are  insoluble  in  water,  but  soluble  in  hot  alcohol, 
ether,  chloroform,  etc. 

The  alkaline  soaps  are  soluble  in  water. 


140  ANIMAL  PHYSIOLOGY. 

Most  animal  fats  are  mixtures  of  several  kinds  in  varying 
proportion  ;  hence  the  melting-point  for  the  fat  of  each  species 
of  animal  is  different. 

PECULIAR  FATS. 

Lecithin,  Protagon,  Cerebrin : 

They  consist  of  C,  H,  N,  O,  and  the  first  two  of  P  in  addi- 
tion. 

They  occur  in  the  nervous  tissues. 

CAEBOHYDRATES. 

General  formula,  Cm  (H20)„. 

1.  The  Sugars  :  Dextrose,  or  grape-sugar,  CeHiaOe  +  H2O 
readily  undergoes  alcoholic  fermentation;  less  readily  lactic 
fermentation. 

Lactose,  milk-sugar,  Ci2H220n  +  H2O  ;  susceptible  of  the  lactic 
acid  fermentation. 

Inosit,  or  muscle-sugar,  C6H12O6  +  2H2O;  capable  of  the  lac- 
tic fermentation. 

Maltose,  C12H22O11  +  H2O,  capable  of  the  alcoholic  fermenta- 
tion.    The  chief  sugar  of  the  digestive  process. 

All  the  above  are  much  less  sweet  and  soluble  than  ordinary 
cane-sugar. 

2.  The  Starches  :  Glycogen,  CeHioOs,  convertible  into  dex- 
trose. Occurs  abundantly  in  many  foetal  tissues  and  in  the 
liver,  especially  of  the  adult  animal. 

Dextrin,  CeHioOe,  convertible  into  dextrose.  Soluble  in 
water ;  intermediate  between  starch  and  dextrose ;  a  product 
of  digestion. 

Pathological:  Grape-sugar  occurs  in  the  urine  in  diabetes 
mellitus. 

Certain  substances  formed  within  the  body  may  be  regarded 
as  chiefly  waste-products,  the  result  of  metabolism  or  tissue- 
changes. 

They  are  divisible  into  nitrogenous  metabolites  and  non- 
nitrogenous  metabolites. 

Nitrogenous  Metabolites. 

1.  Urea,  uric  acid  and  compounds,  kreatinin,  xanthin,  hypo- 
xanthin  (sarkin),  hippuric  acid,  all  occurring  in  urine. 

2.  Leucin,  tyrosin,  taurocholic,  and  glycocholic  acids,  which 
occur  in  the  digestive  tract. 


PHYSIOLOGICAL   RESEARCH,   PHYSIOLOGICAL   REASONING.   141 

3.  Kreatin,  constantly  found  in  muscle,  and  a  few  others  of 
less  constant  occurrence. 

The  above  consists  of  C,  H,  N,  O.  Taurocholic  acid  contains 
also  S. 

The  molecule  in  most  instances  is  complex. 

Non- Nitrogenous  Metabolites. 

These  occur  in  small  quantity,  and  some  of  them  are  secreted 
in  an  altered  form. 

They  include  lactic  and  sarcolactic  acid,  oxalic  acid,  succinic 
acid,  etc. 


PHYSIOLOGICAL  RESEARCH  AND  PHYSIOLOGICAL 
REASONING. 

We  propose  in  this  chapter  to  examine  into  the  methods 
employed  in  physiological  investigation  and  teaching,  and  the 
character  of  conclusions  arrived  at  by  physiologists  as  depend- 
ent on  a  certain  method  of  reasoning. 

The  first  step  toward  a  legitimate  conclusion  in  any  one  of 
the  inductive  sciences  to  which  physiology  belongs  is  the  col- 
lection of  facts  which  are  to  constitute  the  foundation  on 
which  the  inference  is  to  be  based.  If  there  be  any  error  in 
these,  a  correct  conclusion  can  not  be  drawn  by  any  reliable 
logical  process.  On  the  other  hand,  facts  may  abound  in  thou- 
sands and  yet  the  correct  conclusion  never  be  reached,  because 
the  method  of  interpretation  is  faulty,  which  is  equivalent  to 
saying  that  the  process  of  inference  is  either  incomplete  or  in- 
correct. The  conclusions  of  the  ancients  in  regard  to  nature 
were  usually  faulty  from  errors  in  both  these  directions;  they 
neither  had  the  requisite  facts,  nor  did  they  correctly  interpret 
those  with  which  they  were  conversant. 

Let  us  first  examine  into  the  methods  employed  by  modern 
physiologists,  and  determine  in  how  far  they  are  reliable.  First, 
there  is  the  method  of  direct  observation,  in  which  no  appara- 
tus whatever  or  only  the  simplest  kind  is  employed ;  thus,  the 
student  may  count  his  own  respirations,  feel  his  own  heart- 
beats, count  his  pulse,  and  do  a  very  great  deal  more  that  will 
be  pointed  out  hereafter ;  or  he  may  examine  in  like  manner  an- 
other fellow-being  or  (me  of  the  lower  animals.  This  method 
is  simple,  easy  of  application,  and  is  that  usually  employed  by 
the  physician  even  at  the  present  day,  especially  in  private 


1^2  ANIMAL  PHYSIOLOGY. 

practice.  The  value  of  the  results  obviously  depends  on  the 
reliability  of  the  observer  in  two  respects :  First,  as  to  the  ac- 
curacy, extent,  and  delicacy  of  his  perceptions ;  and,  secondly, 
on  the  inferences  based  on  these  sense-observations.  Much 
must  depend  on  practice— that  is  to  say,  the  education  of  the 
senses.  The  hand  may  become  a  most  delicate  instrument  of 
observation ;  the  eye  may  learn  to  see  what  it  once  could  not ; 
the  ear  to  detect  and  discriminate  what  is  quite  beyond  the 
uncultured  hearing  of  the  many.  But  it  is  one  of  the  most 
convincing  evidences  of  man's  superiority  that  in  every 
field  of  observation  he  has  risen  above  the  lower  animals, 
some  of  which  by  their  unaided  senses  naturally  excel  him. 
So  in  this  science,  instruments  have  opened  up  mines  of  facts 
that  must  have  otherwise  remained  hidden;  they  have,  as 
it  were,  provided  man  with  additional  senses,  so  much  have 
the  natural  powers  of  those  he  already  possessed  been  sharp- 
ened. 

But  the  chief  value  of  the  results  reached  by  instruments 
consists  in  the  fact  that  the  movements  of  the  living  body  can 
be  registered  ;  i.  e.,  the  great  characteristic  of  modern  physiol- 
ogy is  the  extensive  employment  of  the  graphic  method,  which 
has  been  most  largely  developed  by  the  distinguished  French 
experimenter  Marey.  Usually  the  movements  of  the  point  of 
lever  are  impressed  on  a  smoked  surface,  either  of  glazed 
paper  or  glass,  and  rendered  permanent  by  a  coating  of  some 
material  applied  in  solution  and  drying  quickly,  as  shellac  in 
alcohol.  The  surface  on  which  the  tracing  is  written  may  be 
stationary,  though  this  is  rarely  the  case,  as  the  object  is  to  get 
a  succession  of  records  for  comparison ;  hence  the  most  used 
form  of  writing  surface  is  a  cylinder  which  may  be  raised  or 
lowered,  and  which  is  moved  around  regularly  by  some  sort  of 
clock-work.  It  follows  that  the  lever-point,  which  is  moved  by 
the  physiological  effect,  describes  curves  of  varying  complexity. 
That  tracings  of  this  or  any  other  character  should  be  of  any 
value  for  the  purposes  of  physiology,  they  must  be  susceptible 
of  relative  measurement  both  for  time  and  space.  This  can  be 
accomplished  only  when  there  is  a  known  base-line  or  abscissa 
from  which  the  lever  begins  its  rise,  and  a  time  record  which  is 
usually  in  seconds  or  portions  of  a  second.  The  first  is  easily 
obtained  by  simply  allowing  the  lever  to  write  a  straight  line 
before  the  physiological  effect  proper  is  recorded.  Time  inter- 
vals are  usually  indicated  by  the  interruptions  of  an  electric 
current,  or  by  the  vibrations  of  a  tuning-fork,  a  pen  or  writer 


PHYSIOLOGICAL  RESEARCH,   PHYSIOLOGICAL  REASONING.  I43 

of  some  kind  being  iu  each  instance  attached  to  the  apparatus 
so  as  to  record  its  movements. 

As  levers,  in  proportion  to  their  length,  exaggerate  all  the 
movements  imparted  to  them,  a  constant  process  of  correction 
must  be  carried  on  in  the  mind  in  reading  the  records  of  the 
graphic  method,  as  in  interpreting  the  field  of  view  presented 
by  the  microscope. 

The  student  is  especially  warned  to  carry  on  this  process, 
otherwise  highly  distorted  views  of  the  reality  will  become 
fixed  in  his  own  mind  ;  and  certainly  a  condition  of  ignorance 
is  to  be  preferred  to  such  false  knowledge  as  this  may  become. 
But  it  is  likewise  apparent  that  movements  that  would  without 
such  mechanism  be  quite  unrecognized  may  be  rendered  visible 
and  utilized  for  inference.  There  is  another  source  of  possible 
misconception  in  the  use  of  the  graphic  method.  The  lever  is 
sometimes  used  to  record  the  movements  of  a  column  of  fluid 
(manometer.  Fig.  207),  as  water  or  mercury,  the  inertia  of  which 
is  considerable,  so  that  the  record  is  not  that  of  the  lever  as 
affected  by  the  physiological  (tissue)  movement,  but  that  move- 
ment conveyed  through  a  fluid  of  the  kind  indicated.  Again, 
all  points,  however  delicate,  write  with  some  friction,  and  the 
question  always  arises.  In  how  far  is  that  friction  sufiicient  to 
be  a  source  of  inaccuracy  in  the  record  ?  When  organs  are  di- 
rectly connected  with  levers  or  apparatus  in  mechanical  rela- 
tion with  them,  one  must  be  sure  that  the  natural  action  of  the 
organ  under  investigation  is  in  no  way  modified  by  this  con- 
nection. 

From  these  remarks  it  will  be  obvious  that  in  the  graphic 
method  physiologists  possess  a  means  of  investigation  at  once 
valuable  and  liable  to  mislead.  Already  electricity  has  been 
extensively  used  in  the  researches  of  physiologists,  and  it  is  to 
this  and  the  employment  of  photography  that  we  look  in  the 
near  future  for  methods  that  are  less  open  to  the  objections  we 
have  noticed. 

However  important  the  methods  of  physiology,  the  results 
are  vastly  more  so.  We  next  notice,  then,  the  progress  from 
methods  and  observations  to  inferences,  which  we  shall  en- 
deavor to  make  clear  by  certain  cases  of  a  hypothetical  charac- 
ter. Proceeding  from  the  brain  and  entering  the  substance  of 
the  heart,  there  is  in  vertebrates  a  nerve  known  as  the  vagus. 
Suppose  tliat,  on  stimulating  this  nerve  by  eh-ctricity  in  a  rab- 
bit, tlie  hf;art  ceases  to  beat,  what  is  tlie  legitimate  inference  ? 
Apparently  that  the  effect  has  been  due  to  the  action  of  tlio 


14:4  ANIMAL  PHYSIOLOGY. 

nerve  on  the  heart,  an  action  excited  by  tlie  use  of  electricity. 
This  does  not,  however,  according  to  the  principles  of  a  rigid 
logic,  follow.  The  heart  may  have  ceased  beating  from  some 
cause  wholly  unconnected  with  this  experiment,  or  from  the 
electric  current  escaping  along  the  nerve  and  affecting  some 
nervous  mechanism  within  the  heart,  which  is  not  a  part  of  the 
vagus  nerve  ;  or  it  may  have  been  due  to  the  action  of  the  cur- 
rent on  the  muscular  tissue  of  the  heart  directly,  or  in  some  other 
way.  But  suppose  that  invariably,  whenever  this  experiment 
is  repeated,  the  one  result  (arrest  of  the  beat)  follows,  then  it  is 
clear  that  the  vagus  nerve  is  in  some  way  a  factor  in  the  causa- 
tion. Now,  if  it  could  be  ascertained  that  certain  branches  of 
the  nerve  were  distributed  to  the  heart-muscle  directly,  and  that 
stimulation  of  these  gave  rise  to  arrest  of  the  cardiac  pulsation, 
then  would  it  be  highly  probable,  though  not  certain,  that  there 
was  in  the  first  instance  no  intermediate  mechanism;  while 
this  inference  would  become  still  more  probable  if  in  hearts 
totally  without  any  such  nervous  apparatus  whatever,  such  a 
result  followed  on  stimulation  of  the  vagus.  Suppose,  further, 
that  the  application  of  some  drug  or  poison  to  the  heart  pro- 
vided with  special  nervous  elements  besides  the  vagus  termi- 
nals prevented  the  effect  before  noticed  on  stimulating  the 
vagus,  while  a  like  result  followed  under  similar  circumstances 
in  those  forms  of  heart  unprovided  with  such  nervous  struct- 
ures, there  would  be  additional  evidence  in  favor  of  the  view 
that  the  result  we  are  considering  was  due  solely  to  some  action 
of  the  vagus  nerve ;  while,  if  arrest  of  the  heart  followed  in  the 
first  case  but  not  in  the  second,  and  this  result  were  invariable, 
there  would  be  roused  the  suspicion  that  the  action  of  the 
vagus  was  not  direct,  but  through  the  nervous  structures  with- 
in the  heart  other  than  vagus  endings.  And  if,  again,  there  were 
a  portion  of  the  rabbit's  heart  to  which  there  were  distributed 
this  intrinsic  nervous  supply,  which  on  stimulation  directly 
was  arrested  in  its  pulsation,  it  would  be  still  more  probable 
that  the  effect  in  the  first  instance  we  have  considered  was  due 
to  these  structures,  and  only  indirectly  to  the  vagus.  But  be  it 
observed,  in  all  these  cases  there  is  only  probability.  The  con- 
clusions of  physiology  never  rise  above  probability,  though  this 
may  be  so  strong  as  to  be  practically  equal  in  value  to  absolute 
certainty.  Would  it  be  correct,  from  any  or  all  the  experi- 
ments we  have  supposed  to  have  been  made,  to  assert  that  the 
vagus  was  the  arresting  (inhibitory)  nerve  of  the  heart  ?  All 
hearts  thus  far  examined  have  much  in  common  in  structure 


PHYSIOLOGICAL  RESEAECH,   PHYSIOLOGICAL  REASONING.  I45 

and  function,  and  in  so  far  is  the  above  generalization  probable. 
Such  a  statement  would,  however,  be  far  from  that  degree  of 
probability  which  is  possible,  and  should  therefore  not  be  ac- 
cepted till  more  evidence  has  been  gathered.  The  mere  resem- 
blance in  form  and  general  function  does  not  suffice  to  meet  the 
demands  of  a  critical  logic.  Such  a  statement  as  the  above  would 
not  necessarily  apply  to  the  hearts  of  all  vertebrates  or  even  all 
rabbits,  if  the  experiments  had  been  conducted  on  one  animal 
alone,  for  the  result  might  be  owing  to  a  mere  idiosyncrasy  of 
the  rabbit  under  observation.  The  further  we  depart  from  the 
grouj)  of  animals  to  which  the  creature  under  experiment  be- 
longs, the  less  is  the  probability  that  our  generalizations  for 
the  one  class  will  apply  to  another.  It  will,  therefore,  be  seen 
that  wide  generalizations  can  not  be  made  with  that  amount  of 
certainty  which  is  attainable  until  experiments  shall  have  be- 
come very  numerous  and  widely  extended.  A  really  broad  and 
sound  physiology  can  only  be  constructed  when  this  science 
has  become  much  more  comparative — that  is,  extended  to  many 
more  groups  and  sub-groups  of  animals  than  at  present. 

To  attempt  to  generalize  for  the  heart,  the  kidney,  the  liver, 
etc.,  when  only  the  dog,  cat,  rabbit,  and  frog,  have  been  made 
as  a  rule  the  subjects  of  experiment,  except  for  the  groups  of 
animals  to  which  the  above  belong,  is  not  only  hazardous  but 
positively  illogical ;  while  to  denominate  conclusions  based  on 
such  experiments,  even  when  supplemented  by  the  teachings 
of  disease,  "  human  physiology "  is,  in  the  writer's  opinion,  a 
wholly  unwarrantable  proceeding. 

It  is  this  conviction  which  has  had  much  to  do  with  this 
book  being  written;  to  the  introduction  of  the  comparative 
element ;  and  the  separation  so  frequently  in  form  as  well  as 
in  reality  of  facts  and  inferences.  A  genuine  human  physi- 
ology, with  the  exact  nature  and  value  of  the  inferences  clearly 
stated,  is  yet  to  be  written ;  and  it  seems  not  only  judicious, 
but  demanded  as  a  matter  of  candor  and  honesty,  to  state  at 
the  outset  to  the  student  what  we  feel  able  to  teach  confidently, 
and  what  must  be  jjresented  as  feebly  probable  or  barely  pos- 
sible 

Human  physiology  projxjr  must  of  necessity  be  accumulated 
slowly.  Much  may  be,  indeed  must  be,  inferred  from  the  ex- 
l^eriments  disease  is  making;  still,  certain  forms  of  accident  or 
surgical  operation  provide  the  opportunity  to  investigate  the 
liuinan  body  in  health  or  in  a  moderately  near  approach  to  that 
condition.  Close  self-observation  under  a  variety  of  condi- 
10 


146  ANIMAL  PHYSIOLOGY. 

tions,  so  precisely  defined  as  to  meet  the  demands  of  science, 
may  be  made  by  the  intelligent  student.  Much  of  this  might 
be  verified  in  the  case  of  other  healthy  persons.  Some  of  it  is 
in  certain  respects  of  more  value  than  any  experiments  that 
can  be  made  upon  the  lower  animals,  for  the  latter  can  not 
communicate  to  us  their  sensations;  in  their  case  all  our  in- 
formation must  be  derived  from  the  use  of  our  own  senses, 
mostly  unaided  by  any  reports  of  theirs. 

It  is  not  possible  during  any  experiment,  especially  any  one 
in  which  vivisection  is  employed,  to  observe  the  animal  under 
conditions  that  are  strictly  normal,  for,  by  the  very  nature  of 
the  case,  we  have  rendered  it  abnormal.  We  must  in  all  such 
instances  draw  conclusions  with  corresponding  caution.  It 
will  be  understood  that  the  expression  "conclusive  experi- 
ment," as  applied  to  such  a  case,  is  only  approximately  correct. 

At  the  present  time  it  is  very  common  to  experiment  upon 
organs  disconnected,  either  anatomically  or  physiologically 
(functionally),  from  the  rest  of  the  body  to  a  greater  or  less 
extent.  This  is  termed  the  isolated  method.  It  has  the  advan- 
tage of  being  more  simple,  and  permits  of  the  study  of  certain 
points  apart  from  others — one  factor  being  considered  inde- 
pendently of  the  rest  in  the  physiological  total.  But,  in  draw- 
ing conclusions,  it  is  very  important  in  such  a  case  not  to  forget 
the  premises.  There  is  manifest  danger  of  making  the  gener- 
alization wider  than  the  facts  warrant.  It  is  only  when  such 
experiments  are  supplemented  by  a  great  many  others,  and 
when  judged  in  connection  with  the  action  of  the  organ  under 
consideration,  as  it  is  infl.uenced  by  other  organs,  that  such  re- 
sults can  be  of  great  value  in  building  up  a  normal  physiology. 
To  know,  for  example,  that  the  isolated  heart  behaves  in  a  cer- 
tain manner  is  not  useless  information,  but  its  value  depends 
entirely  on  the  conclusions  drawn  from  it,  especially  as  to  what 
it  is  conceived  as  teaching  of  the  functions  of  the  heart  as  it 
beats  within  the  body  of.  an  animal  while  it  walks,  or  flies,  or 
swims,  in  carrying  out  the  purpose  of  its  being. 

We  have  incidentally  alluded  to  the  teaching  of  disease. 
"  Disease  "  is  but  a  name  for  disordered  function.  One  viewing 
a  piece  of  machinery  for  the  first  time  in  improper  action  might 
draw  conclusions  with  comparative  safety,  provided  he  had  a 
knowledge  of  the  correct  action  of  similar  machines.  Our  ex- 
perience gives  us  a  certain  knowledge  of  the  functions  of  our 
own  bodies.  By  ordinary  observation  and  by  experiment  on 
other  animals  we  get  additional  data,  which,  taken  with  the 


THE  BLOOD.  147 

disordered  action  resulting  from  gross  or  molecular  injury 
(disease),  gives  a  basis  for  certain  conclusions  as  to  the  normal 
functions  of  the  human  body  or  those  of  lower  animals.  This 
information  is  especially  valuable  in  the  case  of  man,  since  he 
can  report  with  a  fair  degree  of  reliability,  in  most  diseased 
conditions,  his  own  sensations. 

It  is  hoped  that  this  brief  treatment  of  the  methods  and 
logic  of  physiology  will  suffice  for  the  present.  Throughout 
the  work  they  will  be  illustrated  in  every  chapter,  though  not 
always  with  distinct  references  to  the  nature  of  the  intellectual 
process  followed. 

Summary. — There  are  two  methods  of  physiological  observa- 
tion, the  direct  and  the  indirect.  The  first  is  the  simplest,  and 
is  valuable  in  proportion  to  the  accuracy  and  delicacy  and 
range  of  the  observer ;  the  latter  implies  the  use  of  apparatus, 
and  is  more  complex,  more  extended,  more  delicate,  and  precise. 
It  is  usually  employed  with  the  graphic  method,  which  has  the 
advantage  of  recording  and  thus  preserving  movements  which 
correspond  with  more  or  less  exactness  to  the  movements  of 
tissues  or  organs.  It  is  valuable,  but  liable  to  errors  in  record- 
ing and  in  interpretation. 

The  logic  of  physiology  is  that  of  the  inductive  sciences.  It 
proceeds  from  the  special  to  the  general.  The  conclusions  of 
physiology  never  pass  beyond  extreme  probability,  which,  in 
some  cases,  is  practically  equal  to  certainty.  It  is  especially 
important  not  to  make  generalizations  that  are  too  wide. 


THE  BLOOD. 

It  is  a  matter  of  common  observation  that  the  loss  of  the 
whole,  or  a  very  large  part,  of  the  blood  of  the  body  entails 
death  ;  while  an  abundant  haemorrhage,  or  blood-disease  in  any 
of  its  forms,  causes  great  general  weakness. 

The  student  of  embryology  is  led  to  inquire  as  to  the  neces- 
sity for  the  very  early  appearance  and  the  rapid  development 
of  the  blood-vascular  system  so  prominent  in  all  vertebrates. 

An  examination  of  the  means  of  transit  of  the  blood,  as 
already  intimated,  reveals  a  complicated  system  of  tubes  dis- 
tributed to  every  organ  and  tissue  of  the  body.  These  facts 
would  lead  one  to  suppose  that  the  blood  must  have  a  ti-an- 
-cendent  importance  in  the  economy,  and  such,  upon  tlie  most 
minute  investigation,  proves  to  be  the  case.     The  blood  has 


148 


ANIMAL  PHYSIOLOGY. 


been  aptly  compared  to  an  internal  world  for  the  tissues,  an- 
swering to  the  external  world  for  the  organism  as  a  whole. 
This  fluid  is  the  great  storehouse  containing  all  that  the  most 
exacting  cell  can  demand ;  and,  further,  is  the  temporary 
receptacle  of  all  the  waste  that  the  most  busy  cell  requires  to 
discharge.  Should  such  a  life-stream  cease  to  flow,  the  whole 
vital  machinery  must  stop — death  must  ensue. 

Comparative.— It-will  prove  more  scientific  and  generally  sat- 
isfactory to  regard  the  blood  as  a  tissue  having  a  fluid  and 
flowing  matrix,  in  which  float  cellular  elements  or  corpuscles — 
a  view  of  the  subject  that  is  less  startling  when  it  is  remem- 
bered that  the  greater  part  of  the  protoplasm  which  makes  up 
the  other  tissues  of  the  body  is  of  a  semifluid  consistence.  In 
all  animals  possessing  blood,  the  matrix  is  a  clear,  usually  more 
or  less  colored  fluid.  Among  invertebrates  the  color  may  be 
pronounced :  thus,  in  cephalopods  and  some  crustaceans  it  is 
blue,  but  in  most  groups  of  animals  and  all  vertebrates  the 
matrix  is  either  colorless  or  more  commonly  of  some  slight 
tinge  of  yellow.  Invertebrates  with  few  exceptions  possess 
only  colorless  corpuscles,  but  all  vertebrates  have  colored  cells 
which   invariably  outnumber  the  other  variety,  and  display 

forms  and  sizes  which 
are  sufficiently  constant 
to  be  characteristic.  In 
all  groups  below  mam- 
mals the  colored  corpus- 
cles are  oval,  mostly  bi- 
convex, and  nucleated 
during  all  periods  of  the 
animal's  existence  ;  in 
mammals  they  are  cir- 
cular biconcave  disks 
(except  in  the  camel 
tribe,  the  corpuscles  of 
which  are  oval),  and  in 
post-embryonic  life  with- 
out a  nucleus  ;  nor  do 
they  possess  a  cell-wall. 
The  red  cells  vary  in  size 
in  different  groups  and 
sub-groups  of  animals,  being  smaller  the  higher  the  place  the 
animal  occupies,  as  a  general  rule :  thus,  they  are  very  large 
in  vertebrates  below  mammals,  in  some   cases  being  almost 


Fig.  143.— Leucocytes  of  human  blood,  showing  amce- 
boid  movements  (Landois).  These  movements  are 
not  normalli^  in  the  blood-vessels  so  marked  as  pic- 
tured here,  so  that  the  figure  represents  an  ex- 
treme case. 


THE  BLOOD. 


149 


Fig. 


144.— Photograph  of  colored  corpuscles  of 
frog.    1  X  370.    (After  Flint.) 


visible  to  tlie  unaided  eye,  while  in  the  whole  class  of  mam- 
mals they  are  very  minute  ;   their  numbers  also  in  this  group 
are  vastly  greater  than  in 
others  lower  in  the  scale. 

The  average  size  in  man 
is  s^o  inch  ("0077  mm.)  and 
the  number  in  a  cubic  mil- 
limetre of  the  blood  about 
5,000,000  for  the  male  and 
500,000  less  for  the  female, 
which  would  furnish  about 
250,000,000,000  in  a  pound 
of  blood.  It  will  be  under- 
stood that  averages  only  are 
spoken  of,  as  all  kinds  of 
variations  occur,  some  of 
which  will  be  referred  to 
later,  and  their  significance 
explained. 

Under  the  microscope  the  blood  of  vertebrates  is  seen  to 
owe  its  color  to  the  cells  chiefly,  and,  so  far  as  the  red  goes, 

almost  wholly.  Corpuscles 
when  seen  singly  are  never 
of  the  deep  red,  however, 
of  the  blood  as  a  whole, 
but  rather  a  yellowish  red, 
the  tinge  varying  some- 
what with  the  class  of  ani- 
mals from  which  the  spec- 
imen has  been  taken. 

Certain  other  morpho- 
logical elements  found  in 
mammalian  blood  deserve 
l)rief  mention,  though  their 
significance  is  as  yet  a  mat- 
ter of  much  dispute : 

1.    The     blood  -  plates 

Wflorwi  ciiskK,  which  are  many  of  them  arranged     (  plaqUBS,  h<Bmatoblasts , 

third  element),  very  small, 
'olorless,  biconcave  disks,  which  are  dejiosited  in  groat  num- 
bers on  any  thread  or  similar  foreign  body  introduced  into  the 
circulation,  and  rapidly  break  up  when  blood  is  shed. 

2.  On  a  slide  of  blood  that  has  been  prepared  for  some  little 


F)0.  14.5.— 0>rpuBcle8  from  human  subject  (Funke). 
A  few  colorles.s  cftrpuscles  are  seen  among  the 


150 


ANIMAL   PHYSIOLOGY. 


time,  aggregations  of  very  minute  granules  {elementary  gran- 
ules) may  be  seen.  These  are  supposed  to  represent  the  disin- 
tegrating protoplasm  of  the  corpuscles. 


s 

•0 


/> 


Fig.  146. — Blood-plaques  and  their  derivatives  (Landois,  after  Bizzozero  and  Laker).  1,  red 
blood-corpuscles  on  the  flat ;  2,  from  the  side  ;  3,  unchanged  blood- plaques  ;  4,  lymph- 
corpuscle  surrounded  with  blood-plaques  ;  5,  blood-plaques  variously  altered  ;  6,  lymph- 
corpuscle  with  two  masses  of  fused  blood-plaques  and  threads  of  fibrin  ;  7,  group  of 
blood-plaques  fused  or  run  together  ;  8,  similar  small  mass  of  partially  dissolved  blood- 
plaques  with  fibrils  of  fibrin. 

The  pale  or  colorless  corpuscles  are  very  few  in  number  in 
m.ammals  compared  with  the  red,  there  being  on  the  average 
only  about  1  in  400  to  600,  though  they  become  much  more 
numerous  after  a  meal.  They  are  granular  in  appearance,  and 
possess  one  or  more  nuclei,  which  are  not,  however,  readily  seen 
in  all  cases  without  the  use  of  reagents.  They  are  character- 
ized by  greater  size,  a  globular  form,  the  lack  of  pigment,  and 
the  tendency  to  amoeboid  movements,  which  latter  may  be  ex- 
aggerated in  disordered  conditions  of  the  blood,  or  when  the 
blood  is  withdrawn  and  observed  under  artificial  conditions. 
It  will  be  understood  that  these  cells  (leucocytes)  are  not  con- 
fined to  the  blood,  but  abound  in  lymph  and  other  fluids. 
They  are  the  representatives  of  the  primitive  cells  of  the  em- 
bryo, as  is  shown  by  their  tendency  (like  ova)  to  throw  out 
processes,  develop  into  higher  forms,  etc.  In  behavior  they 
strongly  suggest  Amceba  and  kindred  forms. 

We  may,  then,  say  that  in  all  invertebrates  the  blood,  when 
it  exists,  consists  of  a  plasma  (licjuor  sanguinis),  in  which  float 
the  cellular  elements  which  are  colorless;  and  that  in  verte- 
brates in  addition  there  are  colored  cells  which  are  always  nu- 
cleated at  some  period  of  their  existence.     The  colorless  cells 


THE   BLOOD. 


151 


are  globular  masses  of  protoplasm,  containing  one  or  more 
nuclei,  and  with  the  general  character  of  amoeboid  organisms. 


The  History  of  the  Blood-Cells. 

We  have  already  seen  that  the  blood  and  the  vessels  in 
which  it  flows  have  a  common  origin  in  the  mesoblastic  cells  of 
the  embryo  chick ;  the  same  applies  to  mammals  and  lower 
groups.  The  main  facts  may  be  grouped  under  two  head- 
ings: 1.  Development  of  the  blood-corpuscles  during  embry- 
onic life.  2.  Development  of  the  corpuscles  in  ]30st-embryonic 
life. 

In  the  bird  and  the  mammal,  cells  of  the  mesoblast  in  the 
area  opaca  give  off  processes  which  unite;  later  they  become 
hollowed  out  (vacuolated), 
and  thus  form  capillaries. 
At  the  same  time  the  nuclei 
of  these  cells  multiply  ( pr-o- 
l if e rate),  gather  small  por- 
tions of  the  protoplasm  of 
the  main  cells  about  them, 
become  colored,  and  thus 
form  the  nucleated  corpus- 
cles of  the  embryo.  This, 
or  a  similar  process,  is  known 
to  occur  in  some  animals 
(rat)  after  birth ;  but  in  the 
human  f  cetus  there  is  a  grad- 
ual decline  in  the  number  of 
nucleated  cells  found  free  in 

the  blood,  and  at  birth  they    Fjg  147.-Surface  view  from  below  of  a  small  por- 
'  •'  tion  of  posterior  end  of  pellucid^area  of  a  cmck 

are  very  rare,  which  is  prob- 
ably the  case  with  most 
mammals. 

While  the  origin  of  the 
red  cells,  as  above  descfiljed,  may  be  regarded  as  the  earliest 
and  most  general,  it  is  not  their  exclusive  source. 

When  the  liver  has  been  formed  this  organ  seems  to  carry 
on  a  development  begun  in  tlie  spleen,  for  the  nucleated  but  as 
yet  colorless  cells  formed  in  the  spleen  seem  to  become  pig- 
mented in  the  liver. 

There  is  also  evidence  that  colored  corjjuscles  may  arise  by 
endogenous  formation  in  the  lymphatic  glands. 


of  thirty-six  hours,  1  x  4()0  (Foster  and  Bal- 
four), h.  c.  lilood-corpuscles  ;  a,  nuclei,  which 
subsequently  become  nuclei  of  cells  forming 
walls  of  Ijlood-vessels  ;  p.  \)r.  protoplasmic 
processes,  containing  nuclei  with  large  nu- 
cleoli, >i. 


152 


ANIMAL  PHYSIOLOGY. 


There  is  no  doubt  that  the  greater  number  of  the  non-nucle- 
ated corpuscles  are  derived  from  the  nucleated  forms. 

The  post-embryonic  development  of  colored  corpuscles  is 
naturally  less  understood  from  the  greater  difl&culties  attend- 


®    ®  m  ® 


Fig.  148. 


Fig.  149. 


a     3 


1 

© 


^  f©c^ 


Fig.  151. 


Fig.  152. 


Fig.  148.— Cell  elements  of  red  marrow,  n,  large  granular  marrow  cells  ;  &,  smaller,  more 
vesicular  cells  ;  c,  free  nuclei,  or  small  lymphoid  cells,  some  of  which  may  be  even  sur- 
rounded with  a  delicate  rim  of  protoplasm ;  d,  nucleated  red  corpuscles  of  the  bone 
marrow. 

Fig.  149. — Nucleated  red  cells  of  marrow,  iOustrating  mode  of  development  into  the  ordinary 
non-nucleated  red  corpuscles,  a,  common  forms  of  the  colored  nucleated  cells  of  red  mar- 
row ;  6,  1, 2, 3,  gradual  disappearance  of  the  nucleus  ;  c,  large  non-nucleated  red  corpuscle 
resembling  2  and  3  of  b,  in  all  respects  save  in  the  absence  of  any  trace  of  nucleus. 

Fig.  150.— Nucleated  red  corpuscles,  illustrating  the  migration  of  the  nucleus  from  the  cell,  a 
process  not  unfrequently  seen  in  the  red  marrow. 

Fig.  151. — Blood  of  embryo  of  four  months,  a,  1,  2,  3,  4,  nucleated  red  corpuscles.  In  4  the 
same  granular  disintegrated  appearance  of  the  nucleus  as  is  noted  in  marrow  cells,  b,  1, 
microcyte  ;  2,  megalocyte  ;  3,  ordinary  red  corpuscle. 

Fig.  152.— From  spleen.  1,  blood-plaques,  colorless  and  varying  a  little  in  size  ;  2,  two  micro- 
cytes  of  a  deep-red  color  ;  3,  two  ordinary  red  corpuscles  ;  4,  a  solid,  translucent,  lymphoid 
cell  or  free  nucleus.     (Figs.  148-152,  after  Osier.) 

ing  its  investigation.     The  following  may  be  regarded  as  a 
summary  of  the  chief  facts  or  rather  opinions  on  this  subject : 

1.  From  the  colorless  cells ;  though,  whether  the  nucleus 
disappears,  or  remains  to  form  the  chief  part  of  the  cell  and 
become  pigmented,  is  undetermined. 

2.  From  peculiar  cells  of  the  red  marrow  of  the  bones  (head, 
trunk,  etc.),  though  there  is  also  some  doubt  as  to  whether  the 


THE   BLOOD.  I53 

nuclei  of  these  cells  remain  or  not ;  but  as  all  grades  of  transi- 
tion forms  have  been  found  in  the  bone-marrow ;  since  anaemia 
occurs  in  disease  of  bones;  since  the  bone-marrow  has  been 
found  in  an  unusually  active  condition  after  haemorrhage  and 
imder  other  circumstances  demanding  a  rapid  replacement  of 
lost  cells — there  seems  to  be  little  room  for  doubt  that  in  the 
adult  the  red  marrow  of  the  bones  is  the  chief  site  of  the  devel- 
opment of  red  corpuscles.  It  is  not,  however,  the  only  one,  for 
under  peculiar  stress  of  need  even  the  lymphatic  glands  pro- 
duce red  cells,  and  the  latter  have  been  seen  to  be  budded  off 
from  the  spleen  in  a  young  animal  (kid). 

The  colorless  cells  of  the  blood  first  arise  as  migrated  undif- 
ferentiated remnants  of  the  early  embryonic  cell  colonies.  That 
they  remain  such  is  seen  by  their  physiological  behavior,  to  be 
considered  a  little  later.  Afterward  they  are  chiefly  produced 
from  a  peculiar  form  of  connective  tissue  known  as  leucocy- 
tenic,  and  which  is  gathered  into  organs,  the  chief  function  of 
which  (lymphatic  glands)  is  to  produce  these  cells,  though  this 
tissue  is  rather  widely  distributed  in  the  mammalian  body  in 
other  forms  than  these. 

.  Smninary. — The  student  may,  with  considerable  certainty, 
consider  the  colorless  corpuscle  of  the  blood  as  the  most  primi- 
tive ;  the  red,  derived  either  from  the  white  or  some  form  of 
more  specialized  cell ;  the  nucleated,  as  the  earlier  and  more 
youthful  form  of  the  colored  corpuscle,  which  may  in  some 
groups  of  vertebrates  be  replaced  by  a  more  specialized  (or  de- 
graded ?)  non-nucleated  form  mostly  derived  directly  from  the 
former ;  that  in  the  first  instance  the  blood-vessels  and  blood 
arise  simultaneously  in  the  mesoblastic  embryonic  tissue ;  that 
such  an  origin  may  exist  after  birth,  either  normally  in  some 
mammals  or  under  unusual  functional  need ;  that  the  red 
marrow  is  the  chief  birthplace  of  colored  cells  in  adult  life ; 
that  the  spleen,  liver,  lymphatic  glands,  and  other  tissues  of 
similar  structure  contribute  in  a  less  degree  to  the  develop- 
ment of  tlie  red  corpuscles ;  and  that  the  last  mentioned  organs 
are  the  chief  producers  of  the  colorless  amoeboid  blood-cells. 

Finally,  it  is  well  to  remember  that  Nature's  resources  in 
this,  as  in  many  other  cases,  are  numerous,  and  that  her  mode 
of  procedure  is  not  invariable ;  and  tliat,  if  one  road  to  an  end  is 
blocked,  another  is  taken. 

The  Decline  and  Death  of  the  Blood-Cells. — Th(!  blood -corpuscles, 
like  oUu-v  cf^lls,  li;ivc  a  limited  durat  ion,  with  the  usual  chai)ters 
in  a  biological  history  oi  rise,  maturity,  and  decay.     There  is 


154  ANIMAL  PHYSIOLOGY. 

reason  to  believe  tliat  the  red  cells  do  not  live  longer  than  a 
few  weeks  at  most.  The  red  cells,  in  various  degrees  of  disor- 
ganization, have  been  seen  within  the  white  cells  {pliagocytes) , 
and  the  related  cells  of  the  spleen,  liver,  bone-marrow,  etc.  In 
fact,  these  cells,  by  virtue  of  retained  ancestral  {amoeboid)  quali- 
ties, have  devonred  the  weakened,  dying  red  cells.  It  seems  to 
be  a  case  of  survival  of  the  fittest.  It  is  further  known  that 
abundance  of  pigment  containing  iron  is  found  in  both  spleen 
and  liver ;  and  there  seems  to  be  no  good  reason  for  doubting 
that  the  various  pigments  of  the  secretions  of  the  body  {urine, 
hile,  etc.)  are  derived  from  the  universal  pigment  of  the  blood. 
These  coloring  matters,  then,  are  to  be  regarded  as  the  excreta 
in  the  first  instance  of  cells  behaving  like  amoeboids,  and  later 
as  the  elaborations  of  certain  others  in  the  kidney  and  else- 
v^^here,  the  special  function  of  which  is  to  get  rid  of  waste 
products.  The  birth-rate  and  the  death-rate  of  the  blood- 
cells  must  be  in  close  relation  to  each  other  in  health ;  and 
some  of  the  gravest  disturbances  arise  from  decided  changes 
in  the  normal  projiortions  of  the  cells  {anoe.mia,  leucocythe- 
mia). 

Both  the  red  and  white  corpuscles  show,  like  all  other  cells 
of  the  organism,  alterations  corresponding  to  changes  in  the 
surrounding  conditions.  The  blood  may  be  withdrawn  and  its 
cells  more  readily  observed  than  those  of  laost  tissues ;  so  that 
the  study  of  the  influence  of  temperature,  feeding  of  the  leuco- 
cytes, and  the  action  of  reagents  in  both  classes  of  cells  is  both 
of  practical  importance  and  theoretic  interest,  and  will  well  re- 
pay the  student  for  the  outlay  in  time  and  labor,  if  attention  is 
directed  chiefly  to  the  results  and  the  lessons  they  convey,  and 
not,  as  too  commonly  happens,  principally  to  the  methods  of 
manipulation. 

The  Chemical  Composition  of  the  Blood, — Blood  has  a  decided 
but  faint  alkaline  reaction,  owing  chiefly  to  the  presence  of 
sodium  biphosphate  (N"a2HP04),  a  saline  taste,  and  a  faint  odor 
characteristic  of  the  animal  group  to  which  it  belongs,  owing 
probably  to  volatile  fatty  acids.  The  specific  gravity  of  blood 
varies  between  1045  and  1075,  with  a  mean  of  1055 ;  the  spe- 
cific gravity  of  the  corpuscles  being  about  1105  and  of  the 
plasma  1027.  This  difference  explains  the  sinking  of  the  cor- 
puscles in  blood  withdrawn  from  the  vessels  and  kept  quiet. 
Much  the  same  difiiculties  are  encountered  in  attempts  at  the 
exact  determination  of  the  chemical  composition  of  the  blood, 
as  in  the  case  of  other  living  tissues.     Plasma  alters  its  phys- 


THE  BLOOD.  I55 

ical  and  its  chemical  composition,  to  what  extent  is  not  exactly 
known,  when  removed  from  the  body. 

Composition  of  Serum. — The  liuid  remaining  after  coagulation 
of  the  blood  can,  of  course,  be  examined  chemically  with  con- 
siderable thoroughness  and  confidence. 

By  far  the  greater  part  of  serum  consists  of  water;  thus,  it 
has  been  estimated  that  of  100  parts  the  following  statement 
will  represent  fairly  well  the  proportional  comj)osition : 

Water 90  parts ; 

Proteids 8  to  9     " 

Salines,  fats,  and  extractives  (small  in 
quantity  and  not  readily  obtained 
free) 1  to  2  parts. 

The  proteids  are  made  up  of  two  substances  which  can  be 
distinguished  by  solubility,  temperature  at  which  coagulation 
occurs,  etc.,  known  as  paraglohulin  and  serum-albumen,  and 
which  may  exist  in  equal  amount. 

It  is  not  possible,  of  course,  to  say  whether  these  substances 
exist  as  such  in  the  living  blood-plasma  or  not. 

The  fats  are  very  variable  in  quantity  in  serum,  depend- 
ing on  a  corresponding  variability  in  the  plasma,  in  which 
they  would  be  naturally  found  in  greatest  abundance  after 
a  meal.  They  exist  as  neutral  stearin,  palmitin,  olein,  and  as 
soaps. 

The  principal  extractives  found  are  urea,  creatin,  and  allied 
bodies,  sugar,  and  lactic  acid.  Serum  in  most  animals  contains 
more  of  sodium  salts  than  the  corpuscles,  while  the  latter  in 
man  and  some  other  mammals  contain  a  preponderating  quan- 
tity of  potassium  compounds. 

The  princi^jal  salts  of  serum  are  sodium  chloride,  sodium  bi- 
carbonate, sodium  sulphate,  and  phosphate  in  smaller  quantity, 
as  also  of  calcium  and  magnesium  phosphate,  with  rather  more 
of  potassium  chloride. 

It  is  highly  probable  that  this  proportion  also  represents 
moderately  well  the  composition  of  plasma,  which  is,  of  course, 
from  a  ])]iysiological  point  f)f  view,  the  important  matter. 

The  Composition  of  the  Corpuscles. — Taken  together,  the  differ- 
ent forms  of  blood-cells  make  up  from  one  tliird  to  nearly  one 
half  the  weight  of  the  blood,  and  of  this  the  red  corpuscles  may 
be  considered  as  constituting  nearly  the  whole. 

The  coloi'less  cells  are  known  to  contain  fats  and  glycogen, 
which,  with  salts,  we  may  boli(;ve  exist  in  the  living  cells,  and, 
in  addition  t«>  the  proteids,  into  which  protoplasm  resolves  it- 


156  ANIMAL  PHYSIOLOGY. 

self  upon  the  disorganization  that  constitutes  its  dying,  lecithin, 
protagon,  and  other  extractives^ 

The  prominent  chemical  fact  connected  with  the  red  corpus- 
cles is  their  being  composed  in  great  part  of  a  peculiar  colored 
proteid  compound  containing  iron. 

This  will  be  fully  considered  later ;  but,  in  the  mean  time,  we 
may  state  that  the  haemoglobin  is  itself  infiltrated  into  the 
meshes  or  framework  (stroma)  of  the  corpuscle,  which  latter 
seems  to  be  composed  of  a  member  of  the  globulin  class,  so  well 
characterized  by  solubility  in  weak  saline  solutions. 

The  following  tabular  statement  represents  the  relative  pro- 
portions in  100  parts  of  the  dried  organic  matter  of  the  red  cor- 
puscles : 

Hsemoglobin 90*54 

Proteids 8-67 

Lecithin 0'54 

Cholesterin 0*25 


100-00 

The  quantity  of  salts  is  very  small,  less  than  one  per  cent 
(inorganic). 

So  much  for  the  results  of  our  analyses ;  but  when  we  con- 
sider the  part  the  blood  plays  in  the  economy  of  the  body,  it 
must  appear  that,  since  the  life-work  of  every  cell  expresses  it- 
self through  this  fluid,  both  as  to  what  it  removes  and  what  it 
adds,  the  blood  can  not  for  any  two  successive  moments  be  of 
precisely  the  same  composition ;  yet  the  departures  from  a  nor- 
mal standard  must  be  kept  within  very  narrow  limits,  other- 
wise derangement  or  possibly  death  results.  We  think  that, 
before  we  have  concluded  the  study  of  the  various  organs  of 
the  body,  it  will  appear  to  the  student,  as  it  does  to  the  writer, 
that  it  is  highly  probable  that  there  are  great  numbers  of  com- 
pounds in  the  blood,  either  of  a  character  unknown  as  yet  to 
our  chemistry,  or  in  such  small  quantity  that  they  elude  detec- 
tion by  our  methods ;  and  we  may  add  that  we  believe  the 
same  holds  for  all  the  fluids  of  the  body.  The  complexity  of 
vital  processes  is  great  beyond  our  comprehension. 

It  must  be  especially  borne  in  mind  that  all  the  pabulum 
for  every  cell,  however  varied  its  needs,  can  be  derived  from 
the  blood  alone ;  or,  as  we  shall  show  presently,  strictly  speak- 
ing from  the  lymph,  a  sort  of  middle-man  between  the  blood 
and  the  tissues. 

The  Quantity  and  the  Distribution  of  the  Blood. — Any  attempt 


THE  BLOOD.  15'j' 

to  estimate  the  total  quantity  of  blood  in  the  body  of  an  animal 
by  bleeding  is  highly  fallacious  for  various  reasons.  It  is  im- 
possible to  withdraw  all  the  blood  from  the  vessels  by  merely 
opening  even  the  largest  of  them,  and,  if  it  were,  the  original 
quantity  would  be  augmented  by  fluid  absorbed  into  them  dur- 
ing the  very  act.  No  method  has  as  yet  been  devised  that  is 
free  from  objection,  hence  the  conclusions  arrived  at  as  to  the 
total  quantity  of  blood  are  not  in  accord ;  and  in  the  nature  of 
the  case  no  accurate  estimate  can  be  made,  but  about  one  thir- 
teenth to  one  fourteenth  may  be  taken  as  a  fair  average ;  so  that 
in  a  man  of  one  hundred  and  forty  pounds  weight  there  should 
be  about  ten  pounds  of  blood ;  but,  of  course,  this  will  vary 
with  every  hour  of  the  day  and  will  be  greatest  after  a  meal. 

As  an  example  of  the  methods  referred  to,  we  give  Welck- 
er's,  which  is  briefly  as  follows :  The  animal  is  bled  to  death 
from  the  carotid;  a  sample  of  the  defibrinated  blood  (1  cc.)  is 
saturated  with  carbon  monoxide  (CO),  which  gives  a  perma- 
nent red  color ;  this  diluted  with  500  cc.  of  water  furnishes  a 
standard  sample.  The  blood-vessels  of  the  animal  are  washed 
out  with  a  "G  per  cent  solution  of  common  salt,  but  the  out- 
flowing stream  is  colorless ;  to  this  is  added  the  fluid  obtained 
by  chopping  up  the  tissues  of  the  animal,  steeping,  washing 
out,  and  pressing.  The  whole  is  diluted  to  give  the  color  of  the 
standard  solution,  from  which  the  amount  of  blood  in  this  mixt- 
ure may  be  calculated,  since  every  500  cc.  answers  to  1  cc.  of 
blood ;  the  blood  obtained  by  bleeding  can,  of  course,  be  accu- 
rately measured. 

It  would  be  slightly  more  accurate  to  make  the  diluted 
blood  of  the  animal  operated  upon  the  standard  without  treat- 
ment with  carbon  monoxide. 

Such  a  method,  though  the  best  yet  devised,  is  open  to  ob- 
jection also,  as  will  occur  to  most  readers. 

The  relative  quantities  of  blood  in  different  parts  of  the 
body  have  been  estimated  to  be  as  follows : 

Liver one  fourth. 

Skeletal  muscles "        " 

Heart,  lungs,  large  arteries,  and  veins.     "        " 
Other  structures "        " 

The  significance  of  this  distribution  will  appear  later. 

The  Coagulation  of  the  Blood. — When  blood  is  removed  from 
it.s  accu.storiied  channels,  it  undergoes  a  marked  chemical  and 
]>hysical  change,  termed  clotting  or  coagulation.  In  the  case 
of  most  vertebrates,  almost  as  soon  as  the  blood  leaves  the  ves- 


158  ANIMAL   PHYSIOLOGY. 

sels  it  begins  to  thicken,  and  gradually  acquires  a  consistence 
that  may  be  compared  to  that  of  jelly,  so  that  it  can  no  longer 
be  poured  from  the  containing  vessel.  Though  some  have  rec- 
ognized different  stages  as  distinct,  and  named  them,  we  think 
that  an  unprejudiced  observer  might  fail  to  see  that  there 
were  any  well-marked  appearances  occurring  invariably  at  the 
same  moment,  or  with  resting  stages  in  the  process,  as  with 
the  development  of  ova. 

After  coagulation  has  reduced  the  blood  to  a  condition  in 
which  it  is  no  longer  diffluent,  minute  drops  of  a  thin  fluid 
gradually  show  themselves,  exuding  from  the  main  mass, 
faintly  colored,  but  never  red,  if  the  vessel  in  which  the  clot 
has  formed  has  been  kept  quiet  so  that  the  red  corpuscles  have 
not  been  disturbed ;  and  later  it  may  be  noticed  that  the  main 
mass  is  beginning  to  sink  in  the  center  {cupping) ;  and  in  the 
blood  of  certain  animals,  as  the  horse,  which  clots  slowly,  the 
upper  part  of  the  coagulum  {crassainentum)  appears  of  a 
lighter  color,  owing,  as  microscopic  examination  shows,  to  the 
relative  fewness  of  red  corpuscles.  This  is  the  buff y-coat,  or,  as 
it  occurs  in  inflammatory  conditions  of  the  blood,  was  termed 
by  older  writers,  the  crusta  phlogistica.  It  is  to  be  distinguished 
from  the  lighter  red  of  certain  parts  of  a  clot,  often  the  result 
of  greater  exposure  to  the  air  and  more  complete  oxidation  in 
consequence.  The  white  blood-cells,  being  lighter  than  the  red, 
are  also  more  abundant  in  the  upper  part  of  the  clot  (buffy- 
coaf).  If  the  coagulation  of  a  drop  of  blood  withdrawn  from 
one's  own  finger  be  watched  under  the  microscope,  the  red  cor- 
puscles may  be  seen  to  run  into  heaps,  like  rows  of  coins  lying 
against  each  other  {rouleaux,  Fig.  145),  and  threads  of  the 
greatest  fineness  are  observed  to  radiate  throughout  the  mass, 
gradually  increasing  in  number,  and,  at  last,  including  the 
whole  in  a  meshwork  which  slowly  contracts.  It  is  the  forma- 
tion of  this  fibrin  which  is  the  essential  factor  in  clotting ;  the 
inclusion  of  the  blood-cells  and  the  extrusion  of  the  serum 
naturally  resulting  from  its  formation  and  contraction. 

The  great  mass  of  every  clot  consists,  however,  of  corpus- 
cles ;  the  quantity  of  fibrin,  though  variable,  not  amounting  to 
more  usually  than  about  '2  per  cent  in  mammals.  The  forma- 
tion of  the  clot  does  not  occupy  more  than  a  few  minutes  (two 
to  seven)  in  most  mammals,  including  man,  but  its  contraction 
lasts  a  very  considerable  time,  so  that  serum  may  continue  to 
exude  from  the  clot  for  hours.  It  is  thus  seen  that,  instead  of 
the  plasma  and  corpuscles  of  the  blood  as  it  exists  within  the 


THE   BLOOD.  159 

living  body,  coagulation  has  resulted  in  the  formation  of  two 
new  products — serum  and  fibrin — differing  both  physically  and 
chemically.     These  facts  may  be  put  in  tabular  form  thus : 

Blood  as  it  flows   j  Liquor  sanguinis  (plasma), 
in  the  vessels.       {  Corpuscles. 

Blood  after  co-     j  Coagulum  |  corpuscles. 

agulation.  j  ^^ 

'^  {  Serum. 

As  fibrin  may  be  seen  to  arise  in  the  form  of  threads,  under 
the  microscope,  in  coagulating  blood,  and  since  no  trace  of  it  in 
any  form  has  been  detected  in  the  plasma,  and  the  process  can 
be  accounted  for  otherwise,  it  seems  unjustifiable  to  assume 
that  fibrin  exists  preformed  in  the  blood,  or  arises  in  any  way 
prior  to  actual  coagulation. 

Fibrin  belongs  to  the  class  of  bodies  known  as  proteids,  and 
can  be  distinguished  from  the  other  subdivisions  of  this  group 
of  substances  by  certain  chemical  as  well  as  physical  charac- 
teristics. It  is  insoluble  in  water  and  in  solutions  of  sodium 
chloride ;  insoluble  in  hydrochloric  acid,  though  it  swells  in 
this  menstruum. 

It  may  be  whipped  out  from  the  freshly  shed  blood  by  a 
bundle  of  twigs,  wires,  or  other  similar  arrangement  present- 
ing a  considerable  extent  of  surface ;  and  when  washed  free 
from  red  blood-cells  presents  itself  as  a  white,  stringy,  tough 
substance,  admirably  adapted  to  retain  anything  entangled  in 
its  meshes.  If  fibrin  does  not  exist  in  the  plasma,  or  does  not 
arise  directly  as  such  in  the  clot,  it  must  have  some  antecedents 
already  existing  as  its  immediate  factors  in  the  plasma,  either 
before  or  after  it  is  shed. 

We  .shall  here  present  certain  facts,  and  examine  the  conclu- 
sions drawn  from  them  afterward  : 

1.  Blood  may  be  prevented  from  coagulating  by  receiving  it 
in  a  solution  of  a  neutral  salt  {magnesium  sidphafe,  etc.),  and 
upon  certain  chemical  treatment  precipitate  a  body  which  may 
be  obtained  by  additional  manipulation  as  a  white,  flaky  sub- 
stance, that  may  be  shown  not  to  be  fibrin,  but  which  will 
'lot  and  so  give  rise  to  this  body.  Such  is  the  plasmine  of 
Denis. 

2.  By  treatment  of  plasma  with  solid  sodium  chloride,  two 
bodies  with  different  coagulating  points,  but  belonging  to  the 
same  gronp  of  proteids  ((jlohulins,  soluble  in  saline  solutions), 
may  be  obtained,  denominated  panujlubulin  and  fibriiiuycn  re- 
-pectively. 


160  ANIMAL   PHYSIOLOGY. 

3.  Paraglobulin  may  be  obtained  from  serum,  also,  and  fibrin- 
ogen from  certain  fluids  occurring  normally  (jje?'/car(f[a7,  jj?f?/- 
ral,  etc.)  or  abnormally  {hydrocele  fluid). 

■4.  Serum  added  to  these  fluids  sometimes  induces  coagula- 
tion. 

5.  Coagulation  may  occur  spontaneously  in  the  above-men- 
tioned fluids  when  removed  from  the  natural  seat  of  their  for- 
mation. 

6.  A  preparation,  made  by  extracting  serum  or  the  -whipped 
(defibrinated)  blood  added  to  specimens  of  certain  fluids  when 
they  do  not  coagulate  spontaneously,  as  hydrocele  fluid,  often 
induces  speedy  clotting. 

7.  This  extract  {fibrin-fennenf)  loses  its  properties  on  boil- 
ing, and  a  very  small  quantity  sufiices  in  most  cases  to  induce 
the  result.  For  these  and  other  reasons  this  agent  has  been 
classed  among  bodies  known  as  uiiorganized  ferments,  y^'hicli 
are  distinguished  by  the  following  properties : 

Thej^  exert  their  influence  only  under  well-defined  circum- 
stances, among  which  is  a  certain  narrow  range  of  tempera- 
ture, about  blood-heat,  being  most  favorable  for  their  action. 
They  do  not  seem  to  enter  themselves  into  the  resulting  prod- 
uct, but  act  from  without  as  it  were  (catalytic  action),  hence  a 
very  small  quantity  sufiices  to  effect  the  result.  In  all  cases 
they  are  destroyed  by  boiling,  though,  they  bear  exposure  for 
a  limited  period  to  a  freezing  temperature. 

The  conclusions  drawn  from  the  above  statements  are  these : 
1.  Coagulation  results  from  the  action  of  a  fibrin -ferment  on 
fibrinogen  and  paraglobulin.  2.  Coagulation  results  from  the 
action  of  a  fibrin-ferment  on  fibrinogen  alone.  3.  Denis  plasmine 
is  made  up  of  fibrinogen  and  paraglobulin. 

From  observations,  microscopic  and  other,  it  has  been  con- 
cluded that  the  corpuscles  play  an  important  part  in  coagula- 
tion by  furnishing  the  fibrin-ferment ;  but  tbe  greatest  diver- 
sity of  opinion  prevails  as  to  which  one  of  the  morphological 
elements  of  the  blood  furnishes  the  ferment,  for  each  one  of 
them  has  been  advocated  as  the  exclusive  source  of  this  fer- 
ment by  different  observers. 

The  above  conclusions  do  not  seem  to  us  to  follow  neces- 
sarily from  the  premises.  It  might  be  true  that  a  solution  of 
fibrinogen,  on  ha^•ing  fibrin-ferment  added  to  it,  would  clot,  and 
yet  it  would  not  follow  that  such  was  the  process  of  coagula- 
tion in  the  blood  itself.  All  specimens  of  hj^drocele  fluid,  and 
similar  ones  not  spontaneously  coagulable,  do  not  clot  when 


THE  BLOOD,  161 

fibrin-ferment  is  added.  Moreover,  fibrin-ferment  has  not  been 
isolated  as  an  absolutely  distinct  chemical  individual,  free  from 
all  impurities. 

Because  fibrinogen  and  paraglobulin  give  rise,  under  certain 
circumstances  (it  is  asserted),  to  fibrin,  and  since  plasmine  acts 
likewise,  it  does  not  follow  that  plasmine  contains  these  bodies. 
Further,  it  is  stated  that  in  the  blood  of  crustaceans  the  clot 
arises  from  the  corpuscles  chiefly,  which  run  together  and 
blend  into  a  homogeneous  mass.  The  fibrin  so  called  in  such 
a  case  differs  not  a  little  chemically,  it  could  probably  be  shown, 
if  our  tests  were  delicate  enough  to  discover  it,  from  that  which 
is  denominated  fibrin  in  other  cases.  "  Fibrin-ferment "  seems 
to  have  been  used  to  cover  much  ignorance  and  unnecessary 
invention,  as  we  shall  endeavor  to  show  later  on ;  and  we  can 
not  but  regard  the  reasoning  in  regard  to  the  coagulation  of 
the  blood  as  evidence  of  an  erroneous  interpretation  of  certain 
facts  on  the  one  hand,  and  a  large  oversight  of  additional  facts 
on  the  other  hand. 

In  the  mean  time  we  turn  to  certain  well-known  phenomena 
which  bear  a  clear  interpretation :  1.  The  blood  remains  fluid 
in  the  vessels  for  some  time  after  the  death  of  an  animal ;  clots 
first  in  the  larger  vessels,  and  keeps  fluid  longest  in  the  smaller 
veins.  2.  The  blood  in  the  heart  of  a  cold-blooded  animal,  as 
that  of  the  frog  or  turtle,  which  will  beat  for  days  after  the 
animal  itself  is  dead,  maintains  its  fluidity,  but  clots  at  once  on 
removal.  3.  The  blood  inclosed  in  a  large  vein  removed  be- 
tween ligatures  does  not  coagulate  for  many  hours  (twenty- 
four  to  forty-eight). 

There  are  also  facts  of  an  opposite  nature,  thus :  1.  When 
blood  passes  from  a  blood-vessel  into  one  of  the  cavities  of  the 
body,  it  clots  as  if  shed  externally.  2.  If  a  ligature  be  passed 
tightly  around  an  artery  so  as  to  rupture  the  elastic  coat,  co- 
agulation ensues  at  the  site  of  the  ligature.  3.  A  similar 
clotting  results  when  the  inner  coat  of  a  blood-vessel  is  dis- 
eased, as  in  the  case  of  roughening  of  the  valves  of  the  heart 
from  inflammation,  or  the  changes  that  give  rise  to  aneurism 
of  an  artery.  4.  A  wire,  thread,  or  other  like  foreign  body, 
introduced  into  a  vein,  is  speedily  covered  with  fibrin. 

These  facts,  and  others  of  like  character,  have  been  inter- 
preted as  indicating  that  the  living  tissues  of  the  blood-vessel  or 
heart  in  some  way  ];revent  coagulation,  but  as  to  details  there 
is  difference  of  opinion.  Some  believe  that  the  fi])rin-ferment 
(essential  to  coagulation,  according  to  their  view)  is  formed  by 
11 


162  ANIMAL  PHYSIOLOGY. 

the  corpuscles  constantly,  but  in  tlie  above  cases  and  during  life 
is  not  effective  because  at  once  removed  by  the  vessel  walls ; 
while  others  are  of  opinion  that  the  living  cells  composing  these 
walls  prevent  the  formation  of  the  ferment. 

Even  when  injected  into  the  blood-vessels,  fibrin-ferment 
does  not  induce  Coagulation,  nor  does  the  constant  death  of  the 
blood-cells,  supposed  thus  to  give  rise  to  this  substance,  cause 
clotting. 

But  the  truth  is,  there  is  no  necessity  for  all  these  somewhat 
artificial  views,  which  seem  to  us  to  smack  more  of  the  labora- 
tory than  of  nature. 

We  would  explain  the  whole  matter  somewhat  thus :  What 
the  blood  is  in  chemical  composition  and  other  properties  from 
moment  to  moment  is  the  result  of  the  complicated  interaction 
of  all  the  various  cells  and  tissues  of  the  body.  Any  one  of 
these,  departing  from  its  normal  behavior,  at  once  affects  the 
blood ;  but  health  implies  a  constant  effort  toward  a  certain 
equilibrium,  never  actually  reached  but  always  being  striven 
after  by  the  whole  organism.  The  blood  can  no  more  maintain 
its  vital  equilibrium,  or  exist  as  a  living  tissue  out  of  its  usual 
environment,  than  any  other  tissue.  But  the  exact  circum- 
stances under  which  it  may  become  disorganized,  or  die,  are 
legion ;  hence,  it  is  not  likely  that  the  blood  always  clots  in 
the  same  way  in  all  groups  of  animals,  or  even  in  the  same 
group.  The  normal  disorganization  or  death  of  the  tissue  re- 
sults in  clotting ;  but  there  may  be  death  without  clotting,  as 
when  the  blood  is  frozen,  in  various  diseases,  etc. 

To  say  that  fibrin  is  formed  during  coagulation  expresses  in 
a  crude  way  a  certain  fact,  or  rather  the  resultant  of  many 
facts.  To  explain :  When  gunpowder  and  certain  other  ex- 
plosives are  decomposed,  the  result  is  the  production  of  cer- 
tain gases.  If  we  knew  these  gases  and  their  mode  of  com- 
position but  in  the  vaguest  way,  we  should  be  in  much  the 
same  position  as  we  are  in  regard  to  the  coagulation  of  the 
blood. 

There  is  no  difficulty  in  understanding  why  the  blood  does 
not  clot  in  the  vessels  after  death  so  long  as  they  live,  nor  why 
it  does  coagulate  upon  foreign  bodies  introduced  into  the  blood- 
stream. So  long  as  it  exists  under  the  very  conditions  under 
which  it  began  its  being,  there  is  no  reason  why  the  blood 
should  become  disorganized  (clot).  It  would  be  marvelous  if 
it  did  clot,  for  then  we  could  not  understand  how  it  could  ever 
have  been  developed  as  a  tissue  at  all.     It  is  just  as  reasonable 


THE   BLOOD.  1(33 

to  ask  why  does  not  a  muscle-cell  become  rigid  (clot)  in  the 
body  during  life. 

Probably  in  no  field  in  physiology  has  so  much  work  been 
done  with  so  little  profit  as  in  the  one  we  are  now  discussing ; 
and,  as  we  venture  to  think,  owing  to  a  misconception  of  the  real 
nature  of  the  problem.  We  can  understand  the  practical  im- 
portance of  determining  what  circumstances  favor  coagulation 
or  retard  it,  both  within  the  vessels  and  without  them ;  but 
from  a  theoretical  point  of  view  the  subject  has  been  exalted  out 
of  all  proportion  to  its  importance;  and  we  should  not  have 
dwelt,  so  long  upon  it,  or  burdened  the  student  with  sop^ie  of 
the  theories  we  have  stated,  except  in  deference  to  the  views 
held  by  so  many  physiologists. 

It  is  not  surprising  that,  looking  at  the  subject  with  a  dis- 
torted mental  perspective,  one  theory  should  have  replaced  an- 
other with  such  rapidity.  It  is,  however,  of  practical  impor- 
tance to  the  medical  student  to  remember  some  of  the  factors 
that  hasten  or  retard,  as  the  case  may  be,  the  coagulation  of  the 
blood.  Coagulation  is  favored  by  gentle  movement,  contact 
with  foreign  bodies,  a  temperature  of  about  38°  to  40°  C,  addi- 
tion of  a  small  quantity  of  water,  free  access  of  oxygen,  etc. 
The  process  is  retarded  by  a  low  temperature,  addition  of 
abundance  of  neutral  salts,  extract  of  the  mouth  of  the  leech, 
peptone,  much  water,  alkalies,  and  many  other  substances. 
The  excess  of  carbonic  anhydride  and  diminution  of  oxygen, 
seem  to  be  the  cause  of  the  slower  coagulation  of  venous  blood, 
hence  the  blood  long  remains  fluid  in  animals  asphyxiated.  A 
little  reflection  suffices  to  explain  the  action  of  most  of  the  fac- 
tors enumerated.  Any  cause  which  hastens  the  disintegration 
of  the  blood-cells  must  accelerate  coagulation  ;  chemical  changes 
underlie  the  changes  in  this  as  in  all  other  cases  of  vital  action. 
Slowing  of  the  blood-stream  to  any  appreciable  extent  likewise 
favors  clotting,  hence  the  explanation-  of  the  success  of  the 
treatment  of  aneurisms  by  jjressure.  It  is  i)lain  that  in  all 
such  cases  the  normal  relations  between  the  blood  and  the  tis- 
sues are  disturbed,  and,  when  this  reaches  a  certain  pcnnt,  death 
(coagulation)  ensues,  as  with  any  other  tissue. 

Clinical  and  Pathological — The  changes  in  the  blood  that 
cliaraclcrize  certain  abnormal  states  are  highly  instructive.  If 
blf>od  from  an  animal  be  injected  into  the  veins  of  one  of  an- 
other species,  the  death  of  tlie  latter  often  results,  owing  to  non- 
adaptation  to  the  blood  already  in  the  ve.s.sels,  and  to  the  tissues 
of  the  creature  generally.    The  corpuscles  V^ ak  up — the  change 


164 


ANIMAL  PHYSIOLOGY. 


of  conditions  has  been  too  great.  Deficiency  in  the  quantity  of 
the  blood  as  a  whole  {oligcemia)  causes  serious  change  in  the 
functions  of  the  body ;  but  that  a  haemorrhage  of  considerable 
extent  can  be  so  quickly  recovered  from  by  many  persons, 
speaks  much  for  the  recuperative  power  of  the  blood-forming 
tissues.  Various  kinds  of  disturbances  in  these  blood-forming 
organs  result  in  either  deficiency  or  excess  of  the  blood-cells, 
and  in  some  cases  the  appearance  of  unusual  forms  of  corpuscles. 
AncBmia  may  arise  from  a  deficiency  either  in  the  numbers 
or  the  quality  of  the  red  cells  ;  they  may  be  too  few,  deficient 


Fig.  157. 

Fig.  153.— Outlines  of  red  corpuscles  in  a  case  of  profound  ansemia.  1,  1,  normal  corpuscles  ; 
2,  large  red  corpuscle — megalocyte  ;  3,  3,  very  irregular  forms— poikilocytes  ;  4,  very 
small,  deep-red  corpuscles — microcytes. 

Fig.  154.— Origin  of  microcytes  from  red  corpuscles  by  process  of  budding  and  fission.  Speci- 
men from  red  marrow. 

Fig.  155.— Nucleated  red  blood-corpuscles  from  blood  in  case  of  leukaemia. 

Fig.  156. — Corpuscles  containing  red  blood-corpuscles.  1,  from  blood  of  child  at  term  ;  2,  from 
blood  of  a  leuksemic  patient. 

Fig.  157.— a,  1,  2,  3,  spleen-cells  containing  red  blood-corpuscles.  6,  from  marrow  ;  1,  ceU  con- 
taining nine  red  corpuscles  ;  2,  cell  with  reddish  granular  pigment ;  3,  fusiform  cell  con- 
taining a  single  red  corpuscle,  c,  connective-tissue  corpuscle  from  subcutaneous  tissue  of 
young  rat,  showing  the  intracellular  development  of  red  blood-corpuscles.  (Figs.  15:3-157, 
after  Osier.) 

in  size,  or  lacking  in  the  normal  quantity  of  haemoglobin.  In 
one  form  {pernicious  ancBmia),  which  often  proves  fatal,  a 
variety  of  forms  of  the  red  blood-cells  may  appear  in  the  blood- 
stream ;  some  may  be  very  small,  some  larger  than  usual,  others 


THE   BLOOD. 


165 


nucleated,  etc.  Again,  the  white  cells  may  be  so  multiplied  that 
the  blood  may  bear  in  extreme  cases  a  resemblance  to  milk. 

In  these  cases  there  has  been  found  associated  an  unusual 
condition  of  the  bone-marrow,  the  lymphatic  glands,  the  spleen, 
and,  some  have  thought,  of  other  parts. 

The  excessive  action  of  these  organs  results  in  the  production 
and  discharge  into  the  blood-current  of  cells  that  are  immature 
and  embryonic  in  character.  This  seems  to  us  an  examjole  of 
a  reversion  to  an  earlier  condition.  It  is  instructive  also  in  that 
the  facts  point  to  a  possible  seat  of  origin  of  the  cells  in  the 
adult,  and,  taken  in  connection  with  other  facts,  we  may  say,  to 
their  normal  source.  These  blood-producing  organs,  having 
too  much  to  do  in  disease,  do  their  work  badly — it  is  incom- 
plete. 

Although  the  evidence,  from  experiment,  to  show  that  the 
nervous  system  in  mammals,  and  especially  in  man,  has  an  in- 
fluence over  the  formation  and  fate  of  the  blood  generally,  is 
scanty,  there  can  be  little  doubt  that  such  is  the  case,  when  we 
take  into  account  instances  that  frequently  fall  under  the  notice 
of  physicians.  Certain  forms  of  anaemia  have  followed  so  di- 
rectly upon  emotional  shocks,  excessiA^e  mental  work  and  worry, 
as  to  leave  no  uncertainty  of  a  connection  between  these  and  the 
changes  in  the  blood ;  and  the  former  must,  of  course,  have  acted 
chiefly  if  not  solely  through  the  nervous  system. 

It  will  thus  be  apparent  that  the  facts  of  disease  are  in  har- 
mony with  the  views  we  have  been  enforcing  in  regard  to  the 
blood,  which  we  may  now  briefly  recapitulate. 

Summary. — Blood  may  be  regarded  as  a  tissue,  with  a  fluid 
matrix,  in  which  float  cell-contents.  Like  other  tissues,  it  has 
its  phases  of  development,  including  origin,  maturity,  and 
death.  The  colorless  cells  of  the  blood  may  be  considered  as 
original  undiff'erentiated  embryo  cells,  which  retain  their  primi- 
tive character ;  the  non-nucleated  red  cells  of  the  adult  are  the 
mature  form  of  nucleated  cells  that  in  the  first  instance  are 
colorless,  and  arise  from  a  variety  of  tissues,  and  which  in 
certain  diseases  do  not  mature,  but  remain,  as  they  originally 
were  at  first,  nucleated.  When  the  red  cells  are  no  longer 
fitted  to  discharge  their  functions,  they  are  in  some  instances 
taken  up  by  amoeboid  organisms  (cells)  of  the  spleen,  liver, 
etc. 

The  chief  function  of  the  red  corpuscles  is  to  convey  oxy- 
gen ;  of  the  white,  to  develop  as  required  into  some  more  differ- 
'•ijtiated  form  of  tissue,  act  as  porters  of  food -material,  and 


^QQ  ANIMAL   PHYSIOLOGY. 

probably  to  take  up  the  work  of  many  other  kinds  of  cells 
when  the  needs  of  the  economy  demand  it.  The  fluid  matrix 
or  plasma  furnishes  the  lymph  by  which  the  tissues  are  direct- 
ly nourished,  and  serves  as  a  means  of  transport  for  the  cells 
of  the  blood. 

The  chemical  composition  of  the  blood  is  highly  complex,  in 
accordance  with  the  function  it  discharges  as  the  reservoir 
whence  the  varied  needs  of  the  tissues  are  supplied ;  and  the 
immediate  receptacle  (together  with  the  lymph)  of  the  entire 
waste  of  the  body ;  but  the  greater  number  of  substances  exist 
in  very  minute  quantities.  The  blood  must  be  maintained  of 
a  certain  composition,  varying  only  within  narrow  limits,  in 
order  that  neither  the  other  tissues  nor  itself  may  suffer. 

The  normal  disorganization  of  the  blood  results  in  coagula- 
tion, by  which  a  substance,  proteid  in  nature,  known  as  fibrin, 
is  formed,  the  antecedents  of  which  are  probably  very  variable 
throughout  the  animal  kingdom,  and  are  likely  so  even  in  the 
same  group  of  animals,  under  different  circumstances ;  and  a 
substa.nce  abounding  in  proteids  (as  does  also  plasma),  known 
as  serum,  squeezed  from  the  clot  by  the  contracting  fibrin.  It 
represents  the  altered  plasma. 

Certain  well-known  inorganic  salts  enter  into  the  composi- 
tion of  the  blood — ^both  plasma  and  corpuscles — but  the  princi- 
pal constituent  of  the  red  corpuscles  is  a  pigmented,  ferrugi- 
nous proteid  capable  of  crystallization,  termed  haemoglobin.  It 
is  respiratory  in  function. 


THE  CONTEACTILE  TISSUES. 

That  contractility,  which  is  a  fundamental  property  in  some 
degree  of  all  protoplasm,  becoming  pronounced  and  definite, 
giving  rise  to  movements  the  character  of  which  can  be  pre- 
dicted with  certainty  once  the  form  of  the  tissue  is  known,  finds 
its  highest  manifestation  in  muscular  tissue. 

Very  briefly,  this  tissue  is  made  up  of  cells  which  may  be 
either  elongated,  fusiform,  nucleated,  finely  striated  lengthwise, 
but  non-striped  transversely,  united  by  a  homogeneous  cement 
substance,  the  whole  constituting  non-striped  or  involuntary 
muscle ;  or,  long  nucleated  fibers  transversely  striped,  covered 
with  an  elastic  sheath  of  extreme  thinness,  bound  together 
into  small  bundles  by  a  delicate  connective  tissue,  these  again 
into  larger  ones,  till  what  is  commonly  known  as  a  "  muscle ^^ 


THE  CONTRACTILE   TISSUES. 


167 


is  formed.  This,  in  the  higher  vertebrates,  ends  in  tough, 
inelastic  extremities  suitable  for  attachment  to  the  levers  it 
may  be  required  to  move  (bones). 


Fio.  158. 


Fig.  159. 


Fig.  1.58.— Muscular  fibers  from  the  urinary  bladder  of  the  human  subject.  1  x  200.  (Sappey.) 
1,  1, 1,  nuclei  ;  2,  2,  2,  borders  of  some  of  the  fibers  :  3,  3,  isolated  fibers  ;  4,  4,  two  fibers 
joined  together  at  5. 

Fig.  1.59.— Muscular  fibers  from  the  aorta  of  the  calf.  1  x  200.  (Sappey.)  1,  1,  fibers  joined 
with  each  other  ;  2,  2,  2,  isolated  fibers. 

Comparative. — The  lowest  animal  forms  possess  the  power  of 
movement,  which,  as  we  have  seen  in  Amoeba,  is  a  result  rather 
of  a  groping  after  food ;  and  takes  place  in  a  direction  it  is  im- 
possible to  predict,  though  no  doubt  regulated  by  laws  definite 
enough,  if  our  knowledge  were  equal  to  the  task  of  defining 
them. 

Those  ciliary  movements  among  the  infusorians,  connected 
with  locomotion  and  the  capture  of  food,  are  examples  of  a  pro- 
toplasmic rhythm  of  wonderful 
beauty  and  simplicity. 

Muscular  tissue  proper  first 
appears  in  the  Codenteruta,  but 
not  as  a  wholly  independent 
tissue  in  all  cases.  In  many 
ffjelenterates  colls  exist,  the  low- 
•T  part  of  which  alone  forms  a 
delicate    muscular    fibei',   wliilo 

the  superficial  portion  (inijoblast),  composing  the  body  of  the 
cell,  may  be   ciliated   and   is   not   contractile   in   any   s])ecial 


■'■»=-"?»».'}■ 


Fig. 


100.— Myoblasts  of  a  jelly-flsh,  the  3/e- 
duHU  Aurclia  (Claus). 


IQQ  ANIMAL  PHYSIOLOGY. 

sense.  The  non-striped  muscle-cells  are  most  abundant  among 
tlie  invertebrates,  though  found  in  the  viscera  and  a  few  other 
parts  of  vertebrates.  This  form  is  plainly  the  simpler  and 
more  primitive.  The  voluntary  muscles  are  of  the  striped 
variety  in  articulates  and  some  other  invertebrate  groups  and 
in  all  vertebrates ;  and  there  seems  to  be  some  relation  between 
the  size  of  the  muscle-fiber  and  the  functional  power  of  the 
tissue — the  finer  they  are  and  the  better  supplied  with  bloody 
two  constant  relations,  the  greater  the  contractility. 

Whether  a  single  smooth  muscle-cell,  a  striped  fiber  {cell),  or 
a  collection  of  the  latter  {muscle)  be  observed,  the  invariable 
result  of  contraction  is  a  change  of  shape  which  is  perfectly 
definite,  the  long  diameter  of  the  cell  or  muscle  becoming 
shorter,  and  the  short  diameter  longer. 

Ciliary  Movements. — This  subject  has  been  already  considered 
briefly  in  connection  with  some  of  the  lower  forms  of  life  pre- 
sented for  study. 

It  is  to  be  noted  that  there  is  a  gradual  replacement  of  this 
form  of  action  by  that  of  muscle  as  we  ascend  the  animal 
scale ;  it  is,  however,  retained  even  in  the  highest  animals  in 
the  discharge  of  functions  analogous  to  those  it  fulfills  in  the 
invertebrates. 

Thus,  in  Vorticella,  we  saw  that  the  ciliary  movements  of 
the  peristome  caused  currents  that  carried  in  all  sorts  of  parti- 
cles, including  food.  In  a  creature  so  high  in  the  scale  as  the 
frog  we  find  the  alimentary  tract  ciliated  ;  and  in  man  himself 
a  portion  of  the  respiratory  tract  is  provided  with  ciliated  cells 
concerned  with  assisting  gaseous  interchange,  a  matter  of  the 
highest  importance  to  the  well-being  of  the  mammal.  As  be- 
fore indicated,  ciliated  cells  are  found  in  the  female  generative 
organs,  where  they  play  a  part  already  explained. 

It  is  a  matter  of  no  little  significance  from  an  evolutionary 
point  of  view,  that  ciliated  cells  are  more  widely  distributed  in 
the  foetus  than  in  the  adult  human  subject. 

As  would  be  expected,  the  movements  of  cilia  are  affected 
by  a  variety  of  circumstances  and  reagents :  thus,  they  are  quick- 
ened by  bile,  acids,  alkalies,  alcohol,  elevation  of  temperature 
up  to  about  40°  C,  etc. ;  retarded  by  cold,  carbonic  anhydride, 
ether,  chloroform,  etc. 

In  some  cases  their  action  may  be  arrested  and  re-estab- 
lished by  treatment  with  reagents,  or  it  may  recommence  with- 
out such  assistance.  All  this  seems  to  point  to  ciliary  action  as 
falling  under  the  laws  governing  the  movements  of  protoplasm 


THE  CONTRACTILE  TISSUES. 


169 


in  general.  It  is  important  to  bear  in  mind  that  ciliary  action 
may  go  on  in  the  cells  of  a  tissue  completely  isolated  from  the 
animal  to  which  it  belongs,  and  though  influenced,  as  just  ex- 
plained, by  the  surroundings,  that  the  movement  is  essentially 
automatic,  that  is,  independent  of  any  special  stimulus,  in  which 
respect  it  differs  a  good  deal  from  voluntary  muscle,  which 
usually,  if  not  always,  contracts  only  when  stimulated. 

The  lines  along  which  the  evolution  of  the  contractile  tissues 
has  proceeded  from  the  indefinite  outflowings  and  withdraw- 
als of  the  substance  of  Amoeba  up  to  the  highly  specialized 
movements  of  a  striped  muscle-cell  are  not  all  clearly  marked 
out ;  but  even  the  few  facts  mentioned  above  suffice  to  show 
gradation,  intermediate  forms.  A  similar  law  is  involved  in 
the  muscular  contractility  manifested  by  cells  with  other  func- 
tions. The  automatic  (self-originated,  independent  largely  of 
a  stimulus)  rhythm  suggestive  of  ciliary  movement,  more 
manifest  in  the  earlier  developed  smooth  muscle  than  in  the 
voluntary  striped  muscle  of  higher  vertebrates,  indicating 
further  by  the  regularity  with  which  certain  organs  act  in 
which  this  smooth  muscular  tissue  is  predominant,  a  relation- 
ship to  ciliary  movement 
something  in  common  as  to 
origin — in  a  word,  an  evo- 
lution. And  if  this  be 
borne  in  mind,  we  believe 
many  facts  will  appear  in 
a  new  light,  and  be  invested 
with  a  breadth  of  meaning 
they  would  not  otherwise 
possess. 

The  Irritability  of  Muscle 
and  Nerve. — An  animal,  as 
a  frog,  deprived  of  its 
brain,  will  remain  motion- 
less till  its  tissues  have 
died,  unless  the  animal  be 
in  some  way  stimulated.  If 
a  muscle  be  isolated  from 
the  body  with  the  nerve  to 
which  it  belongs,  it  will 
also  remain  passive ;  but, 
if  an  electric  current  be  passed  into  it,  if  it  be  pricked,  pinched, 
touched  with  a  liot  l>ody  or  with  certain  chemical  reagents. 


Fig.  101.— Nodes  of  Ranvier  and  lines  of  Froniann 
iRanvier).  A.  Intercostal  nerve  of  the  niinise, 
treated  with  silver  nitrate.  B.  Nerve-fiber  from 
the  sciatic  nerve  of  a  full-ffrown  rabbit.  A,  node 
of  I-Janvier  ;  Jl/,  medullary  substance  rendered 
transparent  }>y  the  action  of  glycerine;  C'Y.  axis- 
cylinder  presi-nting  tlie  lines  of  Fi'omaim,  which 
are  very  distinct  near  the  node.  The  lines  are 
less  marked  at  a  distance  from  the  node. 


170 


ANIMAL   PHYSIOLOGY, 


4_> 


contraction  ensues ;  the  same  happening  if  the  nerve  be  thus 
treated  instead  of  the  muscle.  The  changes  in  the  muscle  and 
the  nerve  will  be  seen  later  to  have  much  in  common ;  the  mus- 
cle alone^  however,  contracts,  und  ergoes  a  visible  change  of  form. 
Now,  the  agent  causing  this  is  a  stimulus,  and,  as  we  have 
seen,  may  be  mechanical,  chemical,  thermal,  electrical,  or  nerv- 
ous. As  both  nerve  and 
muscle  are  capable  of 
being  functionally  af- 
fected by  a  stimulus, 
they  are  said  to  be  irrita- 
hle ;  and,  since  muscle 
does  not  contract  with- 
out a  stimulus,  it  is  said 
to  be  non-automatic. 

Now,  since  muscle  is 
supplied  with  nerves  as 
well  as  blood  -  vessels, 
which  end  in  a  peculiar 
way  beneath  the  muscle- 
covering     {sarcolemma) 

which  is  seen  extending  to  the  terminal  plate,  where    ■;■,-,  -Htp  vpvv   ^mlisstflnr.p  of 
it  disappears  ;  4,  termiSal  plate  situated  beneath  the    ^^  ^^^  ^^^  ^   ^^^  UStanoe  Oi 

the  protoplasm  (end- 
plates),  it  might  be  that 
when  muscle  seemed  to 
be  stimulated,  as  above 
indicated,  the  responsive 
contraction  was  really 
due  to  the  excited  nerve 
terminals ;  and  thus  has 
arisen  the  question.  Is  muscle  of  itself  really  irritable  ? 

What  has  been  said  as  to  the  origin  of  muscular  tissue 


Fig.  163.— Mode  of  termination  of  the  motor  nerves 
(Flint,  after  Rouget).  A.  Primitive  fasciculus  of  the 
thyrohyoid  muscle  of  the  human  subject,  and  its 
nerve-tube :  1,  1,  primitive  muscular  fasciculus  ;  2, 
nerve-tube  ;  3,  medullary  substance  of  the  tube, 


sarcolemma— that  is  to  say,  between  it  and  the  ele- 
mentary flbrillee  ;  5,  5,  sarcolemma.  B.  Primitive 
fasciculus  of  the  intercostal  muscle  of  the  lizard,  in 
which  a  nerve-tube  terminates  :  1,  1,  sheath  of  the 
nerve-tube  ;  2,  nucleus  of  the  sheath  ;  3,  3,  sarco- 
lemma becoming  continuous  with  the  sheath  ;  4, 
medullary  substance  of  the  nerve-tube,  ceasing 
abruptly  at  the  site  of  the  terminal  plate  ;  5,  5,  ter- 
minal plate  ;  6,  6,  nuclei  of  the  plate  ;  7,  7,  granular 
substance  which  forms  the  principal  element  of  the 
terminal  plate  and  which  is  continuous  with  the 
axis-cylinder  ;  8,  8,  undulations  of  the  sarcolemma 
reproducing  those  of  the  fibrillae  ;  9,  9,  nuclei  of  the 
sarcolemma. 


Fig.  163.— Intraflbrillar  terminations  of  the  motor  nerve  in  striated  muscle,  stained  with  gold 

chloride  (Landois). 

points  very  strongly  to  an  affirmative  answer,  though  it  does 
not  follow  that  a  property  once  possessed  in  the  lower  forms  of 


APPLICATIOXS  OF   THE  GRAPHIC   METHOD.  171 

a  tissue  may  not  be  lost  in  the  higher  ;  hence  the  resort  to  ex- 
periments which  have  long  been  thought  to  settle  the  matter : 

1.  The  curare  experiment  may  be  thus  performed :  Lift  up 
the  sciatic  nerve  of  a  frog,  and  ligature  the  whole  limb  (ex- 
clusive of  the  nerve)  so  that  no  blood  may  reach  the  muscles ; 
then  inject  curare,  which  paralyzes  nerves  but  not  muscles, 
into  the  general  circulation  through  the  posterior  lymi^h-sac. 
On  stimulating  the  sciatic  nerve  the  muscles  of  the  leg  beneath 
the  ligature  contract,  while  no  contraction  of  the  muscles  of 
the  opposite  leg  follows  from  stimulation  of  its  sciatic  nerve. 
In  the  latter  case  the  curare  has  reached  the  nerve  terminals 
through  the  blood ;  in  the  former,  these  were  left  uninfluenced 
by  the  poison.  If,  now,  the  muscle  itself  be  directly  stimulated 
in  the  latter  case,  contraction  follows,  from  which  it  is  con- 
cluded that  curare  has  destroyed  the  functional  capacity  of  the 
nerve  {terminals),  but  not  of  the  muscle. 

2.  Stimulation  of  those  parts  of  muscles  in  which  no  nervous 
terminations  have  been  found,  as  the  lower  part  of  the  sartorius 
muscle  in  the  frog,  is  followed  by  contraction. 

3.  Certain  substances  (as  ammonia),  when  applied  directly 
to  the  muscle,  cause  contraction,  but  are  not  capable  of  pro- 
ducing this  effect  when  applied  to  the  nerve. 

From  these  and  various  other  facts  it  may  be  concluded  that 
muscle  possesses  independent  irritability. 


APPLICATIONS  OF  THE  GRAPHIC  METHOD  TO  THE  STUDY 
OF  MUSCLE  PHYSIOLOGY. 

It  is  impossible  to  study  the  physiology  of  muscle  to  the 
I)est  advantage  without  .the  employment  of  the  graphic  method ; 
and,  on  the  other  hand,  no  tissue  is  so  well  adapted  for  investi- 
gation by  tlie  isolated  method — i.  e.,  apart  from  the  animal  to 
which  it  actually  belongs— as  muscle ;  hence  the  convenience  of 
introducing  at  an  early  period  our  study  of  the  physiology  of 
contractile  tissue  and  illustrations  of  the  graphic  method,  the 
general  principles  of  which  have  already  been  considered. 

The  descriptions  in  the  text  will  be  brief,  and  the  student  is 
recommended  to  examine  the  figures  and  accompanying  ex- 
planations with  some  care. 

Chronographs,  Revolving  Cylinders,  etc. — Fig.  164  represents  one 
of  the  (jiirlio.st  Uji-uih  (A  apparatus  for  the  measurement  of  brief 
intervals  of  time,  consisting  of  a  simple  mechanism  for  pro- 


172 


ANIMAL  PHYSIOLOGY. 


ducing  the  movement  of  a  cylinder,  which  may  be  covered  with 
smoked  paper,  or  otherwise  prepared  to  receive  impressions 

made  upon  it  by  a  point  and  capa- 
ble of  being  raised  or  lowered,  and 
its  movements  regulated.  The 
cylinder  is  ruled  vertically  into 
a  certain  number  of  spaces,  so 
that,  if  its  rate  of  revolution  is 
known  and  is  constant  (very  im- 
portant), the  length  of  time  of 
any  event  recorded  on  the  sen- 
sitive surface  may  be  accurately 
known.  This  whole  apparatus 
may  be  considered  a  chrono- 
graph in  a  rough  form. 

But  a  tuning-fork  is  the  most 
reliable  form  of  chronograph, 
provided  it  can  be  kept  in  con- 
stant action  so  long  as  required ; 
and  is  provided  with  a  recording 
apparatus  that  does  not  cause 
enough  friction  to  interfere  with 
its  vibrations. 

Fig.  166  illustrates  one  ar- 
rangement that  answers  these 
conditions  fairly  well. 

The  marker,  or  chronograph, 
in  the  more  limited  sense,  is 
kept  in  automatic  action  by  the  fork  interrupting  the  current 
from  a  battery  at  a  certain  definite  rate  answeiing  to  its  own 
proper  note. 


Fig.  164. — Original  chronometer,  devised  by 
Thomas  Young,  for  measuring  minute 
portions  of  time  (after  McKendrick). 
a,  cylinder  revolving  on  vertical  axis  ; 
6,  weight  acting  as  motive  power  ;  c,  d, 
small  balls  for  regulating  the  velocity 
of  the  cylinder  ;  e,  marker  recording  a 
line  on  cylinder. 


C.                                                     J, 

I. 

} 

b. 

Fig.  165.— Myographic  tracing,  such  as  is  obtained  when  the  cylinder  on  which  it  is  written 
does  not  revolve  during  the  contraction  of  the  muscle  (after  McKendrick). 


Marey's  chronograph,  which  is  represented  at  h  above,  and 
in  more  detail  below,  in  Fig.  167,  consists  of  two  electro-magnets 
armed  with  keepers,  between  which  is  the  writer,  which  has  a 


APPLICATIONS  OF  THE  GRAPHIC  METHOD. 


173 


little  mass  of  steel  attached  to  it,  the  whole  working  in  unison 
with  the  tuning-fork,  so  that  an  interruption  of  the  current 


Fig.  166. — Marey's  chronograph  as  applied  to  revolving  cj'linder  (after  McKendrick).  a.  gal- 
vanic element ;  6,  wooden  stand  bearing  tuning-fork  (tVo  hundred  vibrations  per  second); 
c.  electro-magnet  between  limbs  of  tuning-fork  ;  d.  e,  positions  for  tuning-forks  of  one  hun- 
dred and  fifty  vibrations  per  second  ;  /,  tuning-fork  lying  loose,  which  may  be  applied  to 
d  :  f/.  revolving  cylinder  ;  h,  electric  chronograph  kept  in  vibration  synchronous  with  the 
tuning-fork  interrupter.  The  current  working  the  electro-magnet  from  a  is  interrupted  at 
i.  Foucault's  regulator  is  seen  over  the  clock-work  of  the  cylinder,  a  little  to  the  right 
of  g. 

implies  a  like  change  of  position  of  the  writing-style,  which  is 
always  kept  in  contact  with  the  recording  surface. 


Fio.  167.— Side  view  of  Marey's  chronograph  (after  McKendrick).  a,  a,  coils  of  wire  ;  ft,  b, 
keepers  of  electro-magnets  :  c.  vibrating  style  fixed  to  the  steel  plate  e  ;  rl,  binding  screws 
for  attachment  of  wires  ;  +  from  interrupting  tuning-fork  ;  -  to  tlie  battery. 

Fig.  177  shows  the  arrangements  for  recording  a  single 
niuschi  contraction,  and  Fig.  178  the  cliaracter  of  the  tracing 
ol^tained. 

A  musclo-nervo  preparation,  which  usually  consists  of  the 
gastrocnemius  of  tlie   frog  witli   the  sciatic   nerve   attached, 


174 


ANIMAL  PHYSIOLOGY. 


clamped  by  a  portion  of  the  femur  cut  off  with  the  muscle,  is 
made,  on  stimulation,  to  raise  a  weighted  lever  which  is  at- 
tached to  a  point  writing  on  a 
cylinder  moved  by  some  sort  of 
clock-work.  In  this  case  the 
cylinder  is  kept  stationary  dur- 
ing the  contraction  of  the  mus- 
cle ;  hence  the  records  appear 
as  straight  vertical  lines. 

Fig.  1G8.— Muscle-nerve  preparation,  showing  JTor  recording  mOVemeuts  of 
gastrocnemius  muscle,  sciatic  nerve,  and  n      ,     ,-t 
portion  of  femur  of  frog,  for  attachment  great    rapidity,    SO    that   the   in- 
to a  vise  (after  Rosenthal).  ,             i       n      ,                  n                           ^ 

tervals  between  them  may  be 
apparent,  such  an  apparatus  as  is  figured  below  (Fig.  169)  an- 
swers well,  the  vibrations  of  a  tuning-fork  being  written  on  a 


Fig.  169.— Spring  myograph  of  Du  Bois-Reymond  (after  Rosenthal).    The  arrangements  for 
registering  various  details  are  similar  to  those  for  pendulum  myograph  (Fig.  177). 

blackened  glass  plate,  shot  before  a  chronograph  by  releasing 
a  spring. 

Several  records  may  be  made  successively  by  more  compli- 
cated arrangements,  as  will  be  explained  by  another  figure 
later. 


The  Appakatus  used  for  the  Stimulation  of  Muscle. 

It  is  not  only  important  that  there  should  be  accurate  and 
delicate  methods  of  recording  muscular  contractions,  but  that 


APPLICATIONS   OF   THE  GRAPHIC  METHODo 


175 

and 


tliere  be  equally  exact  methods  of  applying,  regulatin 
measuring  the  stimulus  that  induces  the  contraction. 

Fig.  170  gives  a  representation  of  the  inductorium  of  Du 
Bois-Reymond,  by  which  either  a  single  brief  stimulation  or  a 


Fig.  170. — Du  Bois-Reymond's  inductorium  (after  Rosenthal),  i,  secondary  coil  ;  c,  primary 
coil ;  b,  electro-magnet ;  h,  armature  of  hammer  ;  /,  small  movable  screw.  The  current 
from  battery,  ascending  metal  pillar,  passes  along  hammer,  and  by  screw  gets  into  primary 
coil,  thus  inducing  current  in  secondary  coil.  By  connection  between  primary  coil  and 
wires  around  soft  iron  of  6,  iron  Itecomes  a  magnet,  hammer  is  attracted  from  screw  /, 
and  current  thus  broken  ;  but  when  this  occurs,  soft  iron  ceases  to  be  a  magnet  neces- 
sarily, and,  hammer  springing  back,  the  whole  course  of  events  is  repeated.  This  may 
occur  several  hundred  times  in  a  second.  The  above  may  be  clearer  from  diagram,  Fig. 
171.   By  sliding  secondary  coil  up  and  down,  strength  of  induced  current  can  be  giaduated. 

series  of  such  repeated  with  great  regularity  and  frequency 
may  be  effected.     The  apjjaratus  consists  essentially  of  a  pr.i- 


I'Ui.  )71.— diagrammatic  representation  of  the  u'orking  of  Fig.  170  (after  Rosenthal) 


176 


ANIMAL  PHYSIOLOGY. 


mary  coil,  secondary  coil,  magnetic  interrupter,  and  a  scale  to 
determine  the  relative  strength  of  the  current  employed.  The 
instrument  is  put  into  action  by  one  or  more  of  the  various 
well-known  galvanic  cells,  of  which  Daniell's  are  suitable  for 
most  experiments. 


Fig.  173. 


Fig.  172. 


Fig.  173.  — Pfliiger's  myograph.  The  muscle  may  be  fixed  to  the  vise  C  in  the  moist-chamber, 
the  vise  connecting  with  the  lever  E  E,  the  point  of  which  touches  the  plate  of  smoked 
glass  G.  The  lever  is  held  in  equipoise  by  H.  When  weights  are  placed  in  scale-pan  F, 
the  lever  writes  the  degree  of  extension  effected  (after  Rosenthal). 

Fig.  173.— Tetanizing  key  of  Du  Bois-Reymond  (after  Rosenthal).  Wires  may  be  attached  at  b 
and  c.  When  d  is  down  the  current  is  "  short-circuited,"  i.  e.,  does  not  pass  through  the 
wires,  but  direct  from  c  through  d  to  t»,  or  the  reverse,  since  b,  c,  d  are  of  metal,  and,  on 
account  of  their  greater  cross-section,  conduct  so  much  more  readily  than  the  wires,  a  is 
an  insulating  plate  of  ebonite.    This  form  of  key  is  adapted  for  attachment  to  a  table,  etc. 

The  access  to,  or  exclusion  of  the  current  from,  the  induc- 
torium  is  effected  by  some  of  the  forms  of  keys,  a  specimen  of 
which  is  illustrated  in  Fig.  173. 

The  moist  chamber,  or  some  other  means  of  preventing  the 
drying  of  the  preparation,  which  would  soon  result  in  impaired 
action,  followed  by  death,  is  essential.  A  moist  chamber  con- 
sists essentially  of  an  inclosed  cavity,  in  which  is  placed  some 
wet  blotting-paper,  etc.,  and  is  usually  made  with  glass  sides. 
The  air  in  such  a  chamber  must  remain  saturated  with  moist- 
ure. 


APPLICATIONS  OP  THE  GRAPHIC  METHOD. 


177 


A  good  knowledge  of  the  subject  of  electricity  is  especially 
valuable  to  tlie  student  of  physiology.  But  there  are  a  few  ele- 
mentary facts  it  is  absolutely  necessary  to  bear  in  mind :  1.  An 
induced  current  exists  only  at  the  moment  of  making  or  break- 
ing a  primary  (battery)  current.  2.  At  the  moment  of  making, 
the  induced  current  is  in  the  opposite  direction  to  that  of  the 
primary  current,  and  the  reverse  at  breaking.  3.  The  strength 
of  the  induced  current  varies  with  the  strength  of  the  primary 
current.  4.  The  more  removed  the  secondary  coil  from  the 
primary  the  weaker  the  current  (induced)  becomes. 

The  clock-work  mechanism  and  its  associated  parts,  as  seen 
in  Fig.  174,  on  the  right,  is  usually  termed  a  myograph. 


Fio.  17-1. —Arrangement  of  apparatus  for  transmission  of  muscular  movement  by  tambours 
(after  McKendrick).  a,  galvanic  element ;  b,  primary  coil ;  e,  secondary  coil  of  inducto- 
rium  ;  d,  metronome  for  interrupting  primary  circuit  when  induction  current  is  sent  to 
electrodes  Ic  ;  h.  forceps  for  femur  ;  the  muscle,  which  is  not  here  represented,  is  attached 
to  the  receiving  tambour  y,  by  which  movement  is  transmitted  to  recording  tambour  e, 
which  writes  on  cylinder/. 

Instead  of  muscular  or  other  movements  being  communi- 
cated directly  to  levers,  the  contact  may  be  througli  columns 


Fifi.  17.1.— Tambfjur  of  Marey  (after  McKendrick).  a,  metallic  case  ;  h,  thin  India-rubber  mem- 
brane; r.  thin  disk  of  aluminium  siipporting  lever  rf,  a  Bmall  portion  of  which  only  Is  repre- 
wnti-d  ;  '-.  wn-w  for  placing  Kujijxirt  of  lever  vi-rticully  over  c  ;  f,  metallic  tube  communi- 
cating with  cavity  of  tambour  t(^r  attachiiieut  to  an  India-rubber  tul>e. 


178 


ANIMAL  PHYSIOLOGY. 


of  air,  which,  it  will  be  apparent,  must  be  capable  of  comin-iiiii- 
cating  very  slight  changes  if  the  apparatus  responds  readily  to 
the  alterations  in  volume  of  the  inclosed  air. 

Fig.  175  represents  a  Marey's  tambour,  which  consists  essen- 
tially of  a  rigid  metallic  case  provided  with  an  elastic  top,  to 
which  a  lever  is  attached,  the  whole  being  brought  into  com- 
munication with  a  column  of  air  in  an  elastic  tube.  The  work- 
ing of  such  a  mechanism  will  be  evident  from  Figs.  174  and  176. 


Fig.  176.— Tambours  of  Marey  arranged  for  transmission  of  movement  (after  McKendrick). 
a,  receiving  tambour ;  6,  india-rubber  tube ;  c,  registering  tambour ;  d,  spiral  of  wire, 
owing  to  elasticity  of  which,  when  tension  is  removed  from  a,  the  lever  ascends. 

The  greatest  danger  in  the  use  of  such  apparatus  is  not  fric- 
tion but  oscillation,  so  that  it  is  possible  that  the  original  move- 
ment may  not  be  expressed  alone  or  simply  exaggerated,  but 
also  complicated  by  additions,  for  which  the  apparatus  itself  is 
responsible. 

Apparatus  of  this  kind  is  not  usually  employed  much  for 
experiments  with  muscle ;  such  an  arrangement  is,  however, 
shown  in  Fig.  174,  in  which  all  will  be  seen — a  metronome,  the 
pendulum  of  which,  by  dipping  into  cups  containing  mercury, 
makes  the  circuit.  Such  or  a  simple  clock  may  be  utilized  for 
indicating  the  longer  intervals  of  time,  as  seconds. 


A  Single  Simple  Muscular  Contraction. 

Experimental  Facts. — The  phases  in  a  single  twitch  or  muscu- 
lar contraction  may  be  studied  by  means  of  the  pendulum 


APPLICATIONS  OF   THE   GRAPHIC   METHOD. 
(2 


1T9 


Fio.  177.— Diajframmatie  representation  of  the  pendtilum  myoj^raph.  The  smoked-plass  plate, 
A.  Kwin«H  with  a  pendulum,  li.  Before  an  experiment  is  commeneed  the  pendulum  is 
rainefl  up  to  the  rif^ht  and  kept  in  position  l)y  tlie  tooth,  tt,  eati-hinR  on  tlie  spring  eat  eh,  /). 
On  denresMinK  tlie  cateh,  h,  the  ((lass  plate  lieinK  set  free  swiiiffs  into  the  new  iHisiliun  indi- 
caletl  hy  the  dott»-d  lines,  and  Is  held  tliere  \>y  the  tooth,  ii\  meeting  the  ealeli,  /<'.  In  the 
eourw-of  its  swintc  the  tf)oth,  «.eomin«  into  eontaet  with  I  lie  project  iri(j  steel  rod,  c,  knocks 
it  to  one  side.  irit/»  the  pr>sition  indicated  l)y  the  dotted  line,  c'.  The  rod.  c,  is  in  electric 
continuity  with  the  wire,  .c.  of  the  primary  cidl  of  an  inductlou  machine.     In  like  manner 


ISO 


ANIMAL  PHYSIOLOGY. 


the  screw,  d,  is  in  electric  continuity  with  the  wire,  y,  of  the  same  primarr  coil.  The  screw, 
d.  and  the  rod,  c.  are  provided  with  platinum  points,  and  both  are  insulated  by  means  of 
the  ebonite  block,  <?.  The  cirouit  of  the  primary  coU  to  which  x  and  y  belong  is  closed  as 
long-  as  c  and  d  are  in  contact.  When  in  its  swing  the  tooth,  a',  knocks  c  away  from  rf,  the 
circuit  is  immediately  broken,  and  a  "breaking "  shock  is  sent  through  the  electrodes  con- 
nected with  the  secondary  coil  of  the  machine,  and  so  through  the  nerve.  The  lever,  1,  the 
end  only  of  which  is  shown  in  the  figiu-e.  is  brought  to  bear  on  the  glass  plate,  and  when  at 
rest  describes  an  arc  of  a  circle  of  large  radius.  The  tuning-fork,  /  (.ends  only  seen),  serves 
to  mark  the  time  (.after  Foster). 

myograpli  (Fig.  177).  It  consists  of  a  heavy  pendulum,  wliich 
swings  from  a  position  on  tlie  right  to  a  corresponding  one  on 
the  left,  where  it  is  secured  by  a  catch.  During  the  swing  of 
the  pendulum,  which  carries  a  smoked  glass  plate  (by  means 
of  arrangements  more  minutely  described  below  the  figure),  a 
tuning-fork  writes  its  vibrations  on  the  plate,  on  which  is 
inscribed  the  marking  indicating  the  exact  moment  of  the 
breaking  of  an  electric  current,  which  gives  rise  to  a  muscle 
contraction  that  is  also  recorded  on  the  plate. 

The  tracing  on  analysis  presents :  1.  The  record  of  a  tuning- 
fork  making  one  hundred  and  eighty  ^dbrations  in  a  second. 
3.  The  parallel  markiihg  of  the  lever  attached  to  the  muscle 
before  it  began  to  rise.  3.  A  curve,  at  first  rising  slowly,  and 
then  rapidly  to  a  maximum.  4.  A  curve  of  descent  similar  in 
character,  but  somewhat  more  lengthened. 

We  may  interpret  this  record  somewhat  thus :  1.  A  rise  of 
the  lever  answering  to  the  shortening  of  the  muscle  to  which  it 


Fig.  178.— Moscle-curve  obtained  by  the  pendulum  myograph  (Foster).  Read  from  left  to 
right.  The  latent  period  is  indicated  by  the  space  between  o  and  6,  the  length  of  which  is 
measured  by  the  waves  of  a  tuning-fork,  making  one  hundred  and  eighty  double  vibrations 
in  a  second  :  and  in  Uke  manner  the  duration  of  the  other  phases  of  the  contraction  may 
be  estimated.. 

is  attached  following  upon  the  momentary  induction  shock,  as 
the  entrance  of  the  current  into  the  nerve,  the  stimulation  of 
which  causes  the  contraction,  may  be  called.  2.  A  period  before 
the  contraction  begins,  which,  as  shown  by  the  time  marking, 

occupies  in  this  case  -~,  or  about  -^  of  a  second.    In  the  tracing 

the  upward  curve  indicates  that  the  contraction  is  at  first  rela- 


APPLICATIONS  OF  THE  GRAPHIC  METHOD. 


181 


tively  slow,  then  more  rapid,  and  again  slower,  till  a  brief  sta- 
tionary period  is  reached,  when  the  muscle  gradually  hut  rap- 
idly returns  to  its  previous  condition,  passing  through  the  same 
phases  as  during  contraction  proper.  In  other  words,  there  is 
a  period  of  rising  and  of  falling  energy,  or  of  contraction,  and 
relaxation.  4.  A  period  during  which  invisihle  changes,  as 
will  be  explained  later,  are  going  on,  answering  to  those  in  the 
nerve  that  cause  the  molecular  commotion  in  muscle  which 
precedes  the  visible  contraction  —  the  latent  period,  or  the 
period  of  latent  stimulation. 

The  facts  may  be  briefly  stated  as  follows :  The  stimulation 
of  a  muscle  either  directly  or  through  its  nerve  causes  contrac- 
tion, followed  by  relaxation,  both  of  which  are  preceded  by  a 
latent  period,  during  which  no  visible  but  highly  important 
molecular  changes  are  taking  place.  The  whole  chain  of  events 
is  of  the  briefest  duration,  and  is  termed  a  muscle  contraction. 
The  tracing  shows  that  the  latent  period  occupied  rather  more 
than  y-jT5-  second,  the  period  of  contraction  proper  about  yfg-, 
and  of  relaxation  jIj)  second,  so  that  the  whole  is  usually  begun 
and  ended  within  ^  second;  yet,  as  will  be  learned  later, 
many  chemical  and  electrical  phenomena,  the  concomitants  of 
vital  change,  are  to  be  observed. 

In  the  case  just  considered  it  was  assum.ed  that  the  muscle 
was  stimulated  through  its  nerve.  Precisely  the  same  results 
would  have  followed  had  the  muscle  been  caused  to  contract 
by  the  momentary  apx)lication  of  a  chemical,  thermal,  or  me- 
chanical stimulus. 

If  the  length  of  nerve  between  the  point  of  stimulation  and 
the  muscle  was  considerable,  some  difference  would  be  observed 


Fio.  17ft.— HiaCT'arnmafic  representation  of  the  measurement  of  velocity  of  nervous  Impulse 
(h'osUT).  'i'ra<;inK  tal<en  l»y  pendulum  myop;rui)li  (FiK-  177).  Tlie.  nerve  of  same  muscle- 
nerve  jireparalion  is  stimulat/t-d  in  oni-  <'ase  us  f^ar  as  jjossible  from  nuiHcl(%  in  the  other  as 
near  to  it  as  iH)SKible.  Latent  period  is  ah.  nh',  respectively.  Difference  between  iih  and 
till'  inilicaN's,  of  coursf'.  lenjfth  of  time  occupied  by  nervous  impulse  in  traveling  alon« 
ni;rve  from  tlistant  to  near  point. 


in  the  latent  perifjd  if  in  a  second  case  the  nerve  wcjrt;  stimu- 
lated, say,  close  to  the  muscle.    This  is  represented  in  Fig.  179, 


182  ANIMAL  PHYSIOLOGY. 

in  wliich  it  is  seen  that  the  latent  period  in  the  latter  case  is 
shortened  by  the  distance  from  h'  to  h,  which  mnst  be  owing 
to  the  time  required  for  those  molecular  changes  which,  occur- 
ring in  a  nerve,  give  rise  to  a  contraction  in  the  muscle  to  which 
it  belongs ;  in  fact,  we  have  in  this  method  a  means  of  estimat- 
ing the  rate  at  which  these  changes  pass  along  the  nerve — in 
other  words,  we  have  a  means  of  measuring  the  speed  of  the 
propagation  of  a  nervous  impulse.  The  estimated  rate  is  for  the 
frog  twenty-eight  metres  per  second,  and  for  man  about  thirty- 
three  metres.  As  the  latter  has  been  estimated  for  the  nerve, 
with  its  muscle  in  position  in  the  living  body,  it  must  be  re- 
garded rather  as  a  close  approximation  than  as  exact  as  the 
other  measurements  referred  to  in  this  chapter. 

It  will  be  borne  in  mind  that  the  numbers  given  as  repre- 
senting the  relative  duration  of  the  events  vary  with  the  ani- 
mal, the  kind  of  muscle,  and  a  variety  of  conditions  affecting 
>the  same  animal. 

,    Tetanic  Contraction. 

It  is  well  known  that  a  weight  may  be  held  by  the  out- 
:  Stretched  arm  with  apparently  XJerfect  steadiness  for  a  few 
seconds,  but  that  presently  the  arm  begins  to  tremble  or  vi- 
brate, and  soon  the  weight  must  be  dropped.  The  arm  was 
maintained  in  its  position  by  the  joint  contraction  of  several 
muscles,  the  action  of  which  might  be  described  (traced)  by  a 
writer  attached  to  the  hand  and  recording  on  a  moving  sur- 
face. Such  a  record  would  indicate  roughly  what  had  hap- 
pened ;  but  the  exact  nature  of  a  muscular  contraction  in  such 
a  case  can  best  be  learned  by  laying  bare  a  single  muscle,  say 
in  the  thigh  of  a  frog,  and  arranging  the  experiment  so  that  a 
graphic  record  shall  be  made. 

Using  the  apparatus  previously  described  (Fig.  177),  a  second 
induction  shock  may  be  sent  into  the  muscle  before  the  effect 


Fig.  180.— Tracing  of  a  double  muscular  contraction  (Foster).  A  second  induction  shock  was 
sent  into  muscle  when  it  had  so  far  completed  its  contraction  as  is  indicated  by  beginning 
of  second  rise.    Dotted  line  indicates  what  the  curve  would  have  been  but  for  this. 


APPLICATIONS  OF  THE  GRAPHIC  METHOD. 


183 


of  the  first  has  passed  away,  the  result  depending  on  the  phase 
of  the  contraction,  during  which  the  stimuhis  acts  on  the  mus- 
cle. Thus,  if  a  second  shock  be  applied  during  the  latent  pe- 
riod, no  visible  change  in  the  nature  of  the  muscle-curve  can  be 
seen ;  but  if  during  one  of  the  other  phases  of  contraction,  a  re- 
sult like  that  figured  below  (Fig.  180)  follows.  If  a  series  of 
such  shocks  be  sent  into  the  muscle  before  its  contraction  pe- 
riod is  over,  a  succession  of  curves  may  be  superposed  on  one 


Fig.  181.— Curve  of  imperfect  tetanic  contraction  (Foster).  Uppermost  tracing  indicates  con- 
tractions of  muscle  ;  intermediate,  when  the  shocks  were  given  ;  lower,  time-markings  of 
intervals  of  one  second.  Curve  to  be  read,  like  others,  from  left  to  right,  and  illustrates  at 
the  end  a  '"  contraction  remainder." 

another,  to  the  total  height  of  which,  however,  there  is  a  limit, 
no  matter  what  the  strength  of  the  stimulus  used. 

If  the  stimuli  follow  each  other  with  a  certain  rapidity,  such 
a  tracing  as  that  represented  in  Fig.  181  is  obtained ;  and  if  the 
rapidity  of  the  stimulation  exceeds  a  certain  rate,  the  result  is 
that  seen  in  Fig.  182. 


Fia.  182.— Curve  of  complete  tetanic  contraction  (Foster). 

It  is  possible  to  see  in  these  tracings  a  genetic  relation,  the 
second  figure  being  evidently  derivable  from  the  first,  and  the 
third  from  the  second,  by  the  fusion  of  all  the  curves  into  one 
straight  line. 

If  a  muscle,  isolated  as  wo  have  described,  be  watched  dur- 
ing the  period  that  it  is  writing  the  second  and  the  third 


184  ANIMAL  PHYSIOLOGY. 

tracing,  it  may  be  observed  that,  during  that  corresponding  to 
the  former,  though  it  is  shortened,  it  does  not  remain  equally  so 
throughout,  while  during  the  writing  of  the  third  tracing,  there 
is  no  variation  in  its  condition  appreciable  by  the  eye.  What 
has  happened  is  this :  The  muscle  during  the  condition  figured 
in  the  second  tracing  has  periods  of  alternating  contraction  and 
partial  relaxation,  but  during  the  third  case  the  latter  phase 
has  been  apparently  omitted — the  muscle  remains  in  continuous 
contraction.  In  reality  this  is  not  the  case  unless  we  are  mis- 
taken as  to  the  meaning  of  the  muscle-sound. 

The  Muscle  Tone. — There  are  a  number  of  experimental  facts 
from  which  important  conclusions  have  been  drawn,  to  which 
attention  is  now  directed : 

1.  It  has  been  found  that  a  sound  may  be  heard  in  a  still 
room  when  one  brings  the  muscles  of  mastication  into  action 
by  biting  hard;  or  listens  over  a  contracting  biceps  with  a 
stethoscope,  etc. 

2.  When  the  wires  of  a  telephone  (communicator)  are  con- 
nected with  a  muscle,  a  sound  is  heard  during  the  contraction 
of  the  muscle. 

From  these  facts  it  was  concluded  that  a  muscle  when  con- 
tracting gives  rise  to  a  sound ;  that  tetanus,  as  the  form  of  con- 
traction we  are  describing  is  called,  is  essentially  vibratory  in 
character,  which  seems  to  answer  to  the  graphic  representations 
from  a  muscle  when  in  tetanic  contraction,  and  is  in  harmony 
with  the  case  to  which  we  called  attention  at  the  commence- 
ment of  this  subdivision  of  the  subject.  The  note  heard  cor- 
responded, in  the  case  of  an  isolated  muscle,  to  the  number  of 
stimulations  per  second ;  while  for  muscles  made  to  contract  by 
the  will  the  note  was  always  the  same,  answering  to  about 
forty  vibrations  per  second ;  but  as  forty  stimuli  are  not  re- 
quired within  this  period  of  time  to  induce  tetanus,  it  was 
thought  that  this  note  was  probably  the  harmonic  of  a  lower 
one  answering  to  twenty  vibrations  in  a  second. 

It  has  been  recently  shown  that  a  very  much  smaller  num- 
ber of  vibrations  of  the  muscle  can  give  rise  to  an  audible 
sound,  so  that  the  explanation  it  would  seem  must  now  be 
modified ;  and  it  is  likely  that  some  peculiarities  of  the  ear 
itself  must  be  taken  into  the  account  in  the  explanation.  In 
making  the  observations  referred  to  above  (in  1),  the  student 
will  find  it  very  important  to  be  on  his  guard  against  sources 
of  error,  especially  with  the  use  of  a  stethoscope. 

We  may  safely  conclude  that,  at  all  events,  most  of  the  mus- 


APPLICATIONS  OF  THE  GRAPHIC   METHOD.  185 

cular  contractions  occurring  within  the  living  body  are  tetanic 
— i.  e.,  the  muscle  is  in  a  condition  of  shortening,  with  only  very 
brief  and  slight  phases  of  relaxation ;  and  that  a  comparatively 
small  number  of  individual  contractions  suffice  for  tetanus 
when  caused  by  the  action  of  the  central  nervous  system; 
though,  as  proved  by  experiments  on  muscle  removed  from  the 
body,  they  may  be  enormously  increased.  While  a  few  stimu- 
lations per  second  suffice  to  cause  tetanus,  it  will  also  persist 
though  thousands  be  employed. 

The  Strength  of  the  StimuluB. — We  have  assumed  that  in  the 
cases  of  contraction  thus  far  considered  the  stimulus  was  ade- 
quate to  produce  the  full  amount  of  contraction,  or  as  much  as 
could  be  obtained.  Such  a  contraction  and  such  a  stimulus  are 
spoken  of  as  maximal;  but  the  stimulus  might  fall  a  little 
short  of  this,  and  is  then  termed  sub-maximal ;  or  it  may  be  re- 
garded from  the  point  of  view  of  being  the  least  that  will  cause 
a  contraction,  and  is  then  the  minimal  stimulus. 

It  is  important  to  note  that  any  sudden  change  in  an  electric 
current  will  act  as  an  excitant  to  muscular  contraction,  but 
that  very  considerable  changes  in  the  strength  of  the  current  if 
made  gradually  do  not  react  on  the  muscle.  It  sometimes  hap- 
pens that  a  sudden  onward  push  of  the  secondary  coil  of  an 
induction-machine  will  produce  either  a  tetanus  (though  the 
terminal  wires  or  electrodes  were  arranged  for  a  single  induc- 
tion shock)  or  what  is  known  as  a  supermaximal  contraction — 
i.  e.,  one  in  excess  of  what  could  be  obtained  by  more  gradual 
advances,  which  have  no  effect  usually  after  a  certain  maxi- 
mum of  contraction  is  reached.  This,  we  think,  a  matter  of 
considerable  practical  importance,  and  shall  refer  to  its  signifi- 
cance in  a  later  chapter. 

Since  the  opening  or  closing  of  a  key  which  makes  or  breaks 
the  current  really  implies  a  very  great  change  in  the  strength 
of  the  current  affected  suddenly — that  is  in  fact  from  0  to  some 
-I-  quantity  or  the  reverse — we  find  that  usually  the  most  marked 
contractions  occur  only  at  these  times,  and  this  holds,  whether 
the  current  be  slowly  or  rapidly  made  and  broken  (inter- 
rupted). 

The  nerve  being  the  natural  means  of  conveying  a  stimu- 
lus, it  is  easy  to  understand  how  the  contraction  happens  to 
follow  most  perfectly  and  with  less  strength  of  stimulus  when 
this  structure  is  excited. 


186  ANIMAL  PHYSIOLOGY. 


The  Changes  in  a  Muscle  during  Contraction. 

Though  the  change  in  form  is  very  great  during  the  con- 
traction of  a  muscle,  the  change  in  bulk  is  almost  inappreci- 
able, amounting  to  a  diminution  of  not  more  -than  about  xoVo 
of  the  volume.  In  fact,  according  to  the  latest  investigator, 
there  is  no  diminution  whatever.  A  series  of  levers  may  be 
laid  on  a  muscle  or  the  columns  of  air  in  a  series  of  Marey's 
tambours  may  be  influenced  by  the  contracting  muscle,  and 
from  some  such  apparatus  a  graphic  record  like  that  seen  in 
Fig.  183  may  be  obtained. 

It  is  to  be  observed  that  the  contraction  passes  along  the 
muscle  in  the  form  of  a  wave,  the  size  and  speed  of  which  are 


Fig.  183.— Tracing  of  the  propagation  of  the  muscular  wave.    Chronographic  tracing,  one 
hundred  vibrations  per  second  underneath  (Marey). 

susceptible  of  measurement.  For  the  frog  the  wave-length  is 
estimated  at  from  200  to  400  mm.,  and  the  velocity  at  about  3 
to  4  metres  per  second. 

It  is  probably  rather  greater  in  the  muscles  of  mammals 
and  greater  under  the  more  natural  conditions  of  the  muscle  in 
the  intact  living  body. 

But  since  the  fibers  of  striped  muscle  are  of  very  limited 
length  (30  to  40  mm.),  it  would  seem  that  a  contraction  origi- 
nating in  one  fiber  must  be  capable  of  initiating  a  similar 
action  in  its  neighbor ;  and,  as  the  ends  of  the  fibers  lie  in  con- 
tact, it  is  easy  to  understand  how  the  wave  of  contraction 
spreads.  Normally,  the  contraction  must  pass  from  about  the 
center  of  the  muscle-cell  where  the  nerve  terminates  in  the 
end-plate. 

The  microscopic  changes  occurring  in  contracting  muscle 
are  not  well  understood.  The  living  muscle  of  a  beetle's  thigh 
when  placed  under  a  microscope  may  be  seen  in  contraction — a 
sight  of  the  most  striking  nature,  reminding  one  of  a  billowy, 
tempestuous  sea,  and  by  the  use  of  reagents  the  waves  of  con- 
traction may  be  fixed. 

It  may  be  stated  that  the  parts  distinct  before  remain  so 


APPLICATIONS  OP  THE  GRAPHIC  METHOD. 


187 


during  contraction,  and  that  all  parts  of  the  muscle-substance 
seem  to  share  in  the  changes  of  form  involved. 


The  Elasticity  of  Muscle. 

In  proportion  as  bodies  tend  to  resume  their  original  form 
when  altered  by  mechanical  force  are  they  elastic,  and  the  ex- 
tent to  which  they  do  this  marks  the  limit  of 
their  elasticity. 

If  a  muscle  (best  one  with  bundles  of  fibers 
of  about  equal  length  and  parallel  arrange- 
ment) be  stretched  by  a  weight  attached  to 
one  end,  it  will,  on  removal  of  the  extending 
force,  return  to  its  original  length ;  and  if  a 
series  of  weights  which  differ  by  a  common 
increment  be  applied  in  succession  and  the 
degrees  of  extensions  compared,  as  may  be 
done  by  the  graphic  method,  it  will  be  appar- 
ent that  the  increase  in  the  extension  does  not 
exactly  correspond  with  the  increment  in  the 
weight,  but  is  proportionally  less.  With  an 
inorganic  body,  as  a  watch-spring,  this  is  not 
the  case. 

Further,  the  recoil  of  the  muscle  after  the 
removal  of  the  weight  is  not  perfect  for  all 
weights  ;  but  within  certain  narrow  limits 
this  is  the  case,  i.  e.,  the  elasticity  of  muscle, 
though  slight  (for  it  is  easily  over-extended), 
is  perfect.  When  once  a  muscle  is  over-ex- 
tended, so  weighted  that  it  can  not  reach  its 
original  length  almost  at  once,  it  is  very  slow 
to  recover,  which  exxjlains  the  well-known 
duration  of  the  effects  of  sprains,  no  doubt 
owing  to  some  profound  molecular  change  fig.  i84.-du  Bois-Rey 
associated  with  the  stretching.  tiie"study^*rL'iasUc 

The  tracings  below  show  at  a  glance  the  ptT^'"'' liosinlhait 
difference  between  the  elasticity  of  muscle  It'tL-ia-dto muscie'^s 
and  of  f;i-dinary  bodies.  L'elTs. ""''"*'''  '''"' 

It  is  a  curious  fact  that  a  muscle  during 
the  act  of  contraction  is  more  extensible  than  when  passive ;  a 
disadvantage  from  a  purely  X'hysical  jjoint  of  view,  but  proba- 
bly a  real  advantage  as  tending  to  obviate  sprain  by  prevent- 
ing too  sudden  an  application  of  the  extending  force. 


188  ANIMAL  PHYSIOLOGY. 

It  will  he  borne  in  mind  that  the  limbs  are  held  together  as 
by  elastic  bands  slightly  on  the  stretch,  owing  to  the  elasticity 


Fig.  185.— Illustrations  of  the  difference  in  elasticity  of  inanimate  and  living  matter  (after 
Yeo).  1.  Shows  graphically  behavior  of  a  steel  spring  under  equal  increments  of  weight. 
2.  A  similar  tracing  obtained  from  an  India-rubber  band.  3.  The  same  from  a  frog's 
muscle.  Note  that  the  extension  decreases  with  equal  increments  of  weight,  and  that  the 
muscle  fails  to  return  to  the  original  position  (abscissa)  after  removal  of  the  weight. 

of  the  mnscles.  Now,  as  seen  in  many  tracings  of  muscular 
contraction,  there  is  a  tendency  to  imperfect  relaxation  after 
contraction — the  contraction  remainder  or  elastic  after-effect, 
which  can  be  overcome  by  gentle  traction.  In  the  living  body, 
the  weight  of  the  limbs  and  the  action  of  the  stretched  muscles 
on  the  side  of  the  limb  opposite  to  that  on  which  the  muscles 
in  actual  contraction  are  situated,  combine  to  make  the  action 
of  the  muscle  more  perfect  by  overcoming  this  tendency  to  im- 
perfect relaxation,  which  is  probably  less  marked,  independent 
of  these  considerations,  in  the  living  body.  This  elasticity  of 
living  muscles,  which  is  completely  lost  on  death,  is  a  fair 
measure  of  their  state  of  health  or  organic  perfection.  Hence 
that  hard  (elastic  recoil)  feeling  of  the  muscles  in  young  and 
vigorous  persons,  especially  athletes,  in  whom  muscle  is  brought 
to  the  highest  degree  of  perfection. 

This  property  is  then  essentially  the  outcome  of  vitality, 
which  is  in  a  word  the  foundation  of  the  differences  noted  be- 
tween the  elasticity  of  inorganic  and  organic  bodies.  A  mus- 
cle, the  nutrition  of  which  is  suffering  from  whatever  cause, 
whether  deficient  blood-supply,  fatigue,  or  actual  disease,  is 
deficient  in  elasticity.  We  Avisli  to  emphasize  these  relations, 
for  we  consider  it  very  important  to  avoid  regarding  vital  phe- 
nomena in  the  light  of  physics  merely,  which  the  employment 
of  the  graphic  method  (and  indeed  all  methods  by  which  we  re- 
move living  things  out  of  their  normal  relations)  fosters. 

Electrical  Phenomena  of  Muscle. — Certain  pieces  of  apparatus 


APPLICATIOXS  OF  THE  GRAPHIC  METHOD. 


189 


not  as  yet  referred  to  are  required  to  demonstrate  the  electrical 
condition  of  muscle.  The  galvanometer  suitable  for  physio- 
logical experiments  is  one  having  very  many  coils  of  extreme- 
ly fine  wire,  and  so  adapted  to  indicate  the  presence  of  currents 
of  slight  intensity. 

In  order  that  it  may  be  ascertained  definitely  that  the  cur- 
rents that  deflect  the  galvanometer  needle  do  not  originate  out- 
side of  the  muscle  itself,  non-polarizable  electrodes  very  care- 
fully made  must  be  used,  for  the  contact  of  ordinary  metallic 
electrodes  with  living  tissues  suffices  of  itself  to  generate  an 
electric  current,  as  may  be  simply  illustrated  to  one's  self  by 
placing  two  coins,  one  silver  and  the  other  copper,  in  contact 
with  the  upper  and  under  surfaces  of  the  tongue  respectively, 
and  meeting  in  front ;  a  peculiar  taste  results  from  the  current 
excited. 

The  construction  of  the  non-polarizable  electrodes  common- 
ly employed,  and  as  arranged  for  use,  is  diagrammatically  rep- 
resented below  (Fig.  180). 

Assuming  the  apparatus  for  the  detection  of  electrical  cur- 
rent in  muscle  to  be  in  working  order,  a  muscle  from  one  of 


Fig.  1W5.— Non-polarizable  electrodes  of  Du  Bois-Beymond  (after  Rosenthal!.  At  c.  clay  tip, 
moLstened  with  saline  solution,  is  laid  on  muscle.  Glass  cylinder  a  is  filled  with  strong 
sf>lution  of  zinc  sulphate,  a  good  conductor,  by  which  current  is  conveyed  to  amalgamated 
zinc  plate  6,  and  thence  to  galvanometer. 

the  cold-blooded  animals,  prepared  as  rapidly  and  carefully  as 
possible^  avoiding  all  contact  with  foreign  bodies,  is  cut  across 
the  ends  transversely,  and  placed  on  pads  of  bibulous  yjaper 
moistened  with  physiological  (•0()--75  per  cent)  saline  solution. 
The  non-polarizable  electrodes  connected  with  the  galvanome- 
ter are  brought  in  contact  with  the  muscle.  What  results 
depends  on  the  parts  of  the  muscle  that  touch  the  electrodes, 
and  is  represented  diagramatically  in  Fig.  1S7. 

It  will  be  observed  that  the  diagram  indicates  that  between 
no  current  and  the  strongest  obtainable  there  are  all  shades  of 


190 


ANIMAL  PHYSIOLOGY. 


strength,  according  to  the  parts  of  the  muscle  connected  by  the 
electrodes.     The  strongest  is  that  resulting  when  the  superfi- 


FiG.  187.— Representation  of  electrical  currents  in  a  muscle-rhombus  (after  Rosenthal). 

cial  equator  and  the  transverse  center  are  connected  ;  and  it  is 
found  that  the  nearer  these  points  are  approached  the  stronger 
the  current  becomes,  as  is  indicated  by  the  greater  extent  of 
swing  of  the  galvanometer  needle.  In  connection  with  these  sur- 
prising phenomena,  one  naturally  inquires  whether  such  a  mus- 
cle-current, for  such  it  must  be,  is  natural  or  artificial.  Does 
such  exist  in  a  living  muscle  in  its  position  in  the  body,  or  has 
the  injury  done  to  a  muscle  in  its  preparation  by  section,  re- 
moval from  the  usual  conditions  of  nutrition,  and  such  like 
changes,  been  the  cause  of  the  current  ? 

After  much  investigation,  by  some  of  the  ablest  physiolo- 
gists of  the  day,  different  answers  are  returned  to  these  queries. 

Du  Bois-Reymond  maintains  that  such  currents  are  natural, 
and  may  be  obtained  from  muscle  contracting  in  situ  ;  while 
Hermann  and  others  believe  that  such  a  current  is  owing  to 
the  injury  done  by  the  section,  and  that  the  current  from  the 
equator  to  the  poles  of  the  section  is  due  to  the  fact  that  the 
injured  part  is  negative  to  the  uninjured  region. 

It  is  a  fact  that  if  the  current  be  led  off  from  an  exposed 
muscle  prior  to  section,  it  is  relatively  very  weak.  Further, 
the  electrodes  placed  on  the  uninjured  ventricle  of  an  animal's 


APPLICATIONS  OF  THE  GRAPHIC  METHOD. 


191 


heart  convey  no  current  to  the  galvanometer ;  but  after  section, 
as  in  the  case  of  a  skeletal  muscle,  the  usual  result  follows. 
All  observers,  however,  are  agreed  that  a  current  is  produced 
during  contraction.  Those  not  believing  in  that  just  referred 
to  above  ("  current  of  rest "),  term  this  one  the  "  current  of 
action "" ;  while  the  other  school  names  it  the  negative  variation 
of  the  current  of  rest,  inasmuch  as  the  galvanometer  needle 
swings  in  the  opposite  direction  indicating,  as  they  say,  a 
diminution  in  the  original  current. 

The  presence  of  this  undisputed  current  can  be  made  evident 
by  a  simple  experiment,  without  the  use  of  any  of  the  elabo- 
rate apparatus  noticed  above.     Let  two  frog's  limbs,  with  the 


Fio.  188.— Arranwenient  of  parts  to  show 
secondary  eotitra(;tion  in  muscle 
(after  Rosenthal). 


Fig.  189.— The  same  when  the  primary  cause 
is  in  nerve  (after  Roseutlial). 


nerves  belonging  to  them,  be  prepared  in  good  condition  and 
arranged  as  in  Fig.  188,  so  that  the  nerve  of  A  rests  along  the 
thigh  of  B.  On  stimulating  the  nerve  of  B,  the  muscular  effect 
in  this  limb  is  answered  by  a  similar  one  in  A.  That  this  is  not 
necessarily  due  to  escape  of  the  current  upon  tlie  nerve  of  A, 
may  be  shown  by  putting  a  ligature  around  the  nerve  of  B  below 
the  point  of  application  of  the  current  and  moistening  it  so  as 
to  allow  of  th(!  free  passage  of  the  current.  In  such  cas(>  stimu- 
lation of  the  nerve  o^  B  givt^s  wliolly  negative  results,  })ecause 
the  ligature  has  destroyed  physiological  (molecular)  continuity, 
though  it  does  not  prevent  the  passage  of  the  current.     More- 


292  ANIMAL   PHYSIOLOGY. 

over,  tlie  result  may  be  obtained  by  other  than  electrical 
stimnli. 

The  explanation  of  these  phenomena  of  the  "rheoscopic 
frog"  (physiological  rheoscope)  is  simply  that  the  electrical 
condition  of  B  has  been  suddenly  changed  by  the  passage  of 
the  current  into  the  nerve,  and  that  this  difference  of  electrical 
condition  (potential)  between  the  muscle  of  B  and  A's  nerve 
suffices  to  stimulate  the  muscle  of  A  (one  is  in  fact  +  and  the 
other  — ) ;  hence  the  stimulus  and  the  contraction,  the  nature 
of  which  in  A  is  the  same  as  that  in  B — i.  e.,  a  single  twitch 
in  B  gives  rise  to  the  same  in  A,  and  a  tetanic  contraction  to  a 
tetanic  contraction.  Plainly  the  contraction  of  A  must  be  due 
to  a  current  in  B,  hence  the  proof  that  a  current  actually  exists 
during  the  contraction  of  a  muscle.  It  may  be  noted  that  a 
mere  prick  of  B  will  arouse  in  it  a  contraction  which  is  fol- 
lowed by  the  same  result  as  before  in  A,  so  that  in  this  we  can 
exclude  the  original  stimulating  current  altogether  as  a  pos- 
sible source  of  fallacy,  as  stated  above.  But  one  of  the  most 
striking  proofs  that  there  is  a  current  of  action  (or  negative 
variation),  is  obtained  by  placing  the  nerve  of  such  a  prepara- 
tion as  that  represented  in  B  on  a  contracting  mammalian  heart ; 
with  each  systole  there  is  a  spasm  of  the  frog's  leg. 

It  is  important  to  note  that  the  electric  current  of  muscle, 
however  viewed,  is  an  event  of  the  latent  period.  It  is  asso- 
ciated with  the  chemical  and  all  the  other  molecular  changes 
of  which  the  actual  contraction  is  but  the  outward  and  visible 
sign ;  and  since  the  currents  of  rest  have  an  appreciable  dura- 
tion, wane  with  the  vitality  of  the  tissue,  and  wholly  disappear 
at  death,  they  must  be  associated  with  the  fundamental  facts 
of  organic  life ;  for  it  is  to  be  remembered  that  electrical  cur- 
rents are  not  confined  to  muscle,  but  have  been  detected  in  the 
developing  embryo,  and  even  in  vegetable  protoplasm.  Though 
the  evidence  is  not  yet  complete,  it  seems  likely  that  electrical 
phenomena  may  prove  to  be  associated  with  (we  designedly 
avoid  any  more  definite  expression)  all  vital  phenomena. 

Chemical  Changes  in  Muscle. — In  an  animal,  at  a  variable 
period  after  death,  the  muscles  become  rigid,  producing  that 
stiffness  {rigor  mortis)  so  characteristic  of  a  recent  cadaver. 

The  subject  can  be  studied  in  some  of  its  aspects  to  great 
advantage  in  an  isolated  individual  muscle. 

Three  changes  in  a  muscle  that  has  passed  into  death  rigor 
are  constant  and  pronounced.  The  living  muscle,  either  alka- 
line or  neutral  in  reaction,  has  become   decidedly  acid;  an 


APPLICATIONS  OF  THE  GRAPHIC  METHOD.  19a 

abundance  of  carbonic  anhydride  is  suddenly  given  off ;  and 
myosin,  a  specific  proteid,  lias  been  formed.  That  these  phe- 
nomena have  some  indissoluble  connection  with  each  other  so 
far  as  the  first  two  at  least  are  concerned,  while  not  absolutely 
certain,  seems  probable,  as  will  be  learned  shortly. 

It  will  be  borne  in  mind  that  muscle-fibers  are  tubes  con- 
taining semifluid  protoplasm,  and  that  a  coagulation  of  the 
latter  must  give  rise  to  general  rigor.  This  protoplasmic  sub- 
stance can  be  extracted  at  a  low  temperature  from  the  muscles 
of  the  frog,  and,  as  the  temperature  rises  coagulates  like  blood, 
giving  rise  to  a  clot  (myosin)  and  muscle-serum,  a  fluid  not 
very  unlike  the  serum  of  blood. 

This  myosin  can  also  be  extracted  from  dead  rigid  mus- 
cles by  ammonium  choride,  etc.  It  resembles  the  globulins 
generally,  but  is  less  soluble  in  saline  solutions  than  the  globu- 
lin of  blood  (paraglobulin) ;  is  less  tough  than  fibrin ;  has  a 
very  low  coagulating  point  (55°  to  60°  C.) ;  and  is  somewhat 
jelly-like  in  appearance.  The  clotting  of  blood  and  of  muscle 
is  thus  analogous,  myosin  answering  to  fibrin,  and  there  being 
a  serum  in  each  case,  both  processes  marking  the  permanent 
disorganization  of  the  tissue.  The  reaction  seems  to  be  due  to 
the  formation  of  a  kind  of  lactic  acid,  probably  sarolactic ; 
though  whether  due  to  excessive  production  of  this  acid,  on 
the  death  of  the  muscle,  which  for  some  reason  does  not  remain 
free  in  the  living  muscle,  or  whether  sarcolactic  acid  arises  as 
a  new  product,  is  uncertain.  It  is  certain  that  the  acid  reaction 
of  dead  muscle  is  not  owing  to  carbonic  acid,  for  the  reddened 
litmus  does  not  change  color  on  drying. 

That  a  muscle  in  action  does  use  up  oxygen  and  give  off 
carbonic  anhydride  can  be  definitely  proved ;  though  it  is 
equally  clear  that  the  life  of  a  muscle  is  not  dependent  on  a 
constant  supply  of  oxygen  as  is  that  of  the  individual,  for  a 
muscle  can  live,  even  contract  long  and  vigorously,  in  an  atmos- 
phere free  from  this  gas,  as  in  nitrogen. 

From  the  suddenness  of  the  increase  of  carbonic  anhydride, 
the  onset  of  death  and  rigor  mortis  has  been  compared  to  an 
explosion. 

After  this  the  muscle  becomes  greatly  changed  physically: 
its  elasticity  and  translucency  are  lost;  there  is  absence  of 
muscle-currents ;  it  is  wholly  unirritable,  is  less  extensible — it 
is,  as  before  stated,  firmer — it  is  dead. 

But  these  fundamental  plienomena,  the  increase  of  carbonic 
anhydride  and  the  acid  reaction,  are  observable  after  prolonged 

18 


194  ANIMAL  PHYSIOLOGY. 

tetanus.  It  was,  therefore— putting  all  the  facts  together  that 
we  now  refer  to  and  others,  not  forgetting  that  a  muscle  is 
always  respiring^  inhaling  oxygen,  and  exhaling  carbonic  an- 
hydride— not  unreasonable  to  conclude  that  normal  tetanus 
and  rigor  mortis  were  but  exaggerated  conditions  of  a  natural 
state.  The  coagulation  of  the  muscle  protoplasm  {plasma), 
giving  rise  to  myosin,  was,  however,  a  serious  obstacle  to  the 
adoption  of  this  view.  But  it  has  very  recently  been  urged 
with  great  plausibility  that  an  old  view  is  correct,  viz.,  that 
rigor  mortis  (contracture)  is  the  last  act  of  muscle-life ;  it  is,  in 
fact,  a  prolonged  tetanus  or  contracture,  ending  in  most  cases, 
though  not  all,  in  coagulation  of  the  myosin.  This  state  can 
be  induced  and  recovered  from  in  favorable  cases  by  cutting 
^off  the  blood  from  a  part  by  ligature,  and  later  readmitting  it 
to  the  starving  region.  It  has  been  suggested  that  the  prod- 
ucts of  the  muscle-waste,  usually  washed  away  by  the  blood- 
stream, in  such  an  experiment  and  after  death,  collect  and  act 
as  a. stimulant  to  the  muscle,  causing  it  to  remain  in  permanent 
contraction. 

Th€  other  constituents  of  dead  muscle  and  their  relative 
properties  may  be  learned  from  the  following  table  (Von  Bibra) : 

Water 744*5 

Solids:  Myosin,  elastic  substance,  etc., in- 
soluble in  water. 155'4 

Soluble  proteids .* .       19'3 

Gelatin 207 

Extractives  and  salts 37'1 

Fats 23-0 

255  5—255-5 

Total 1,000 

Among  the  extractives  of  muscle  very  important  is  creatin 
('2  to  "3  per  cent),  a  nitrogenous  crystalline  body.  Certain 
allied  forms,  as  xanthin,  hypoxanthin  (sarkin),  karnin,  taurin 
and  uric  acid,  are  also  found. 

Glycogen  (animal  starch),  very  abundant  in  all  the  tissues, 
including  the  muscles  of  the  embryo,  is  found  in  small  quantity 
in  the  muscles  of  the  adult ;  and  in  the  heart-muscle  a  peculiar 
sugar  {inosit)  is  present. 

It  is,  of  course,  very  difficult  to  say  to  what  extent  the  bodies 
known  as  extractives  exist  in  living  muscle,  though  that  glyco- 
gen, fats,  and  certain  salts  are  normally  present  admits  of  little 
doubt. 


APPLICATIONS   OF  THE   GRAPHIC   METHOD.  195 

There  is  a  coloring  matter  in  muscle,  more  abundant  in  the 
red  muscles  of  certain  animals  than  the  pale,  allied  to  heemo- 
globin,  if  not  identical  with  that  body. 

It  may  be  stated  as  a  fact,  the  exact  significance  of  which 
is  unknown,  that  during  contraction  the  extractives  soluble  in 
water  decrease,  while  those  soluble  in  alcohol  increase. 

It  will,  however,  be  very  plain,  from  what  has  been  stated 
in  this  section,  that  life  processes  and  chemical  changes  are 
closely  associated,  and  to  realize  this  is  worth  much  to  the 
student  of  Nature. 

Thermal  Changes  in  the  Contracting  Muscle. 

Since  very  marked  chemical  changes  accompany  muscular 
contraction,  it  might  be  expected  that  there  would  be  some 
modification  in  temperature,  and  probably  in  the  direction  of 
elevation.  Experiment  proves  this  to  be  the  case.  If  a  ther- 
mometer finelj"  graduated  be  kept  among  the  muscles  of  the 
limb  of  a  mammal  during  the  contractions  that  follow  the 
stimulation  of  the  main  nerve,  a  decided  rise  of  temi^erature 
may  be  noted  during  the  prolonged  tetanus  that  may  be  thus 
originated.  True,  during  the  contraction  of  a  set  of  muscles 
under  such  circumstances,  there  is  a  possible  fallacy,  from  the 
excess  of  blood  going  to  the  parts  owing  to  dilatation  of  the 
blood-vessels,  which  it  would  be  necessary  to  exclude — i.  e.,  we 
must  either  ascertain  that  such  does  not  take  place,  or  take  it 
into  account  as  a  factor  in  the  causation  of  the  rise  of  tempera- 
ture. However,  by  using  a  delicate  thermopyle,  a  muscle  to 
which  no  blood  passes  may  be  shown  to  grow  warmer  during 
contraction. 

But  why  should  a  muscle  when  at  rest,  as  may  be  shown, 
maintain  a  certain  temperature,  unless  chemical  changes  are 
constantly  taking  place  ?  As  already  stated,  such  is  the  case, 
and  the  rise  on  passing  into  tetanus  is  simply  an  expression  of 
increased  chemical  action. 

What  is  the  nature  of  the  combustion  originating  this  heat  ? 
Are  certain  crude  materials  withdrawn  from  the  blood  and 
burned  up  directly  in  the  muscle-substance ;  or  is  the  muscle 
itself  continuously  building  up  and  tearing  down  its  own  sub- 
stance, all  of  which  implies  oxidation  ? 

All  attempts  to  explain  the  facts  apart  from  the  latter  view 
have  been  unsuccessful,  and  we  are  forced  to  conclude  that 
such  is  the  synoptical  statement  of  the  life-history  of  muscle. 


196 


ANIMAL   PHYSIOLOGY. 


No  machine  known  to  ns  resembles  muscle  except  super- 
ficially. The  steam-engine  changes  fuel  into  heat  and  mechani- 
cal motion,  but  there  the  resemblance  ends.  Muscle  changes 
its  food,  or  fuel,  not  directly  into  either  heat  or  motion,  but  into 
itself ;  yet  as  a  machine  it  is  more  effective  than  the  steam- 
engine,  for  more  work  and  less  heat  are  the  outcome  of  its 
activity  than  is  the  case  with  the  steam-engine. 


Ci 


ft  c 


The  Physiology  of  Nerve. 

Muscle  and  nerve  are  constantly  associated  functionally,  and 
have  so  much  in  common  that  it  becomes  desirable  to  study 
them  together.  Much  that  has  been  established  for  muscle 
holds  equally  well  for  nerve  ;  and  the  latter,  though  apparently 
wholly  different  in  structure  at  first  sight,  is  really  not  so. 
Nerve  has  its  protoplasmic  part  (axis-cylinder),  which  is  the 
essential  structure,  its  protective  sheaths,  and  its  nuclei  (nerve- 
corpuscles) 

As  already  indicated,  a  nerve  possesses  irritability,  and, 
since  a  muscle  does  not  respond  to  an  electric  current  sent 
through  a  nerve  except  when  there  is  a 
sudden  change  in  the  strength  of  the 
current,  it  becomes  interesting  to  learn 
why  this  should  be  the  case. 

Experimental. — In  Fig.  190  are  shown 
■\<y  I     ^^i=i;//    diagrammatically  two  muscle-nerve  prep- 

C_^  ^      j^i J        arations,  and  the    apparatus    necessary 

for  applying  a  constant  current  and  a 
(momentary)  induced  current  by  single 
shocks  to  the  nerve. 

A   strength    of    current    sufficient  to 

cause  a  (sub-maximal)  contraction  by  an 

induction  shock  is   determined,  and  the 

inductorium  left  at  this  graduation.     A 

constant  current  of  moderate  strength  is 

allowed  to  pass  into  the  nerves  of  the 

Positfve°*poies  Preparation.     It  is  found  that,  in  the  one 

?hfc^ou^rse''k'SfrSw  ^asc,  the  muscle  contraction  is  increased, 

Ka/ep'SXatihfcii  ^ud  in  the  othcr  diminished  or  absent, 

esSaii?aitered°®'^® '^  when    the   Same   strength   of    induction 

shock  is  sent  into  the  nerve  at  the  points 

below  the  entrance   of  the  constant   current — that  is  to  say, 

the  iri^itabiKty  of  the  nerve  has  been  increased  or  diminished. 


Fig.  190. — Diagrammatic  rep- 
resentation of  the  method 
of  testing  the  excitability 
of  the  nerve  in  electrotonus 

(Landois). 


APPLICATIONS  OP  THE  GRAPHIC  METHOD. 


197 


It  is  found  that  when  the  constant  (polarizing)  current  is  pass- 
ing from  above  downward — that  is,  when  the  cathode  (nega- 
tive pole)  is  on  the  side  toward  the  muscle — the  irritability  of 
the  nerve  is  increased,  and  the  reverse  when  the  opposite  con- 
ditions prevail. 

This  altered  condition  is  known  as  electrotonus.  Unfor- 
tunately this  term  is  used  somewhat  loosely,  sometimes  being 
employed  in  the  sense  now  explained ;  sometimes  to  denote 
a  change  of  electro-motive  force  that  accompanies  the  altera- 
tion of  irritability ;  and  again  to  cover  all  the  conditions  implied 
in  the  experiment.  It  is  a  fact  that  during  the  passage  of  a 
constant  current  the  natural  nerve-current  is  affected,  being 
increased  or  diminished  according  to  the  direction  of  the  polar- 
izing current.  There  is,  however,  so  much  difference  of  opinion 
in  regard  to  this  subject  that  it  is  very  doubtful  whether  it 
should  be  more  than  noticed  in  passing. 

But  to  return  to  electrotonus,  which  is  both  interesting  and 
important,  it  has  been  found  as  a  result  of  many  experiments 
that  profound  modifications  of  the  irritability  of  a  nerve  do 
take  place  during  the  passage  of  a  constant  current.  These  are 
diagrammatically  represented  in  Fig.  191. 


Fio.  191.— Diaerrammatic  representation  of  variations  in  electrotonus  according  to  strength  of 
current  employcil  (after  I'lliitceri.  n  /i',  a  section  of  nerve  ;  «.  anode  (+  pole')  ;  k,  kathode 
<—  p<}\e).    Curves  ultove  tli/-  horizontal  denote  katelectrotonus  :  below,  the  opposite. 


Briefly  stated,  they  are  these :  1.  The  nature  of  the  change 
depends  on  the  direction  of  the  polarizing  (constant)  current ; 
hence,  if  the  current  is  descending,  there  is  an  increase  of  irri- 
tability (catelectrotonus)  in  the  portion  of  the  nerve  nearest  the 
muscle,  and  vice  versa.  2.  The  extent  of  the  change  of  irrita- 
bility is  dependent  on  th(;  stnnigth  of  the  polarizing  current. 
3.  This  (diarigo  is  most  niarke<l  close  to  the  electrodes,  spn^ads 
to  a  considerable  extent  })eyond  this  [ioiiit  without  the  elec- 
trodes (extra-j)olar  regions),  and  also  exists  within  the  region 
of  contact  of  tha  electrodes  (intra-polar  rcsgions).     4.  It  f(diows 


198  ANIMAL   PHYSIOLOGY. 

that  there  must  be  a  point  at  which,  it  is  not  experienced  (indif- 
ferent point  or  neutral  point), 

Now,  it  is  possible  to  understand  why  a  sudden  change  in 
the  current  should  cause  a  muscular  contraction.  An  equally 
sudden  change,  a  profound  molecular  effect,  has  been  caused, 
and  this  we  must  believe  essential  to  the  causation  of  a  muscu- 
lar contraction  through  the  influence  of  a  nerve. 

To  use  an  illustration  which  may  serve  a  good  purpose  if 
not  taken  too  literally,  it  is  a  well-known  experience  that  one 
sitting  in  a  room  in  which  a  clock  is  ticking  soon  fails  to  notice 
this  regular  sound ;  but  should  the  clock  stop  suddenly  or  as 
suddenly  commence  to  tick  very  rapidly,  the  attention  is 
aroused,  while  a  very  gradual  slowing  to  cessation  or  the  re- 
verse would  have  escaped  notice.  The  explanation  of  such 
facts  takes  us  down  to  the  very  foundations  of  biology ;  but 
just  now  we  wish  only  to  elucidate  by  our  own  experience 
how  it  is  possible  to  conceive  of  a  muscle  being  stimulated 
by  the  molecular  movements  of  nerve,  or  rather  a  change  in 
these. 

There  are  important  practical  aspects  to  this  question.  One 
may  understand  why  it  is  that  electricity  proves  so  ready  a 
stimulus,  and  is  so  valuable  a  therapeutic  agent.  It  seems, 
in  fact,  as  will  be  learned  later,  to  be  capable  of  taking  the 
place  to  some  extent  of  that  constant  nerve  influence  which 
we  believe  is  being  exerted  in  the  higher  animals  toward 
the  maintenance  of  the  regularity  of  their  cell-life  (metabol= 
ism). 

Pathological  and  Clinical. — It  is  believed  that  in  the  nerves  of 
man,  within  his  living  body,  the  electrotonic  condition  can  be 
induced  as  in  an  isolated  piece  of  nerve.  Hence,  the  value  of 
the  constant  current  in  diminishing  nerve  irritability  in  neu- 
ralgia and  allied  conditions.  Apparatus  of  great  nicety  of  con- 
struction and  capable  of  generating,  accurately  measuring,  and 
conveniently  applying  electrical  currents  of  different  kinds, 
now  adds  to  the  resources  of  the  physician.  But  we  are  prob- 
ably as  yet  only  on  the  threshold  of  electro-therapeutics. 

Law  of  Contraction  (Stimulation). — A  given  piece  of  nerve  is 
stimulated  only  by  the  a]3pearance  of  catelectrotonus,  and  the 
disappearance  of  anelectrotonus ;  but  the  disappearance  of  cat- 
electrotonus and  the  appearance  of  anelectrotonus  are  without 
effect  (Pflliger).  This  so-called  law  is  supposed  to  explain  the 
following  facts,  which  may  be  thus  expressed  in  tabular  form 
(after  Landois) : 


APPLICATIONS  OF  THE  GRAPHIC  METHOD. 


199 


STRENGTH  OF  CURRENT. 


Weak  .. 
Medium. 
Strong  . 


ASCENDING. 

DESCENDING. 

On  closing. 

On  opening. 

On  closing. 

On  opening. 

c 

R 

c 

R 

c 

C 

c 

C 

R 

C 

c 

R 

>  R  =  rest ;  C  =  contraction. 
Electrical  Organs. — Electrical  properties  can  be  manifested 
by  a  large  number  of  fishes ;  and  the  subject  is  of  special 
theoretical  interest.  It  is  now  established  that  the  development 
of  electrical  organs  points  to  their 
being  specially  modified  muscles 
— tissues,  in  fact,  in  which  the 
contractile  substance  has  disap- 
peared and  the  nervous  elements 
become  predominant  and  peculiar. 
No  work  is  done,  but  the  whole  of 
the  chemical  energy  is  represented 
by  electricity.  Functionally  an 
electric  organ  (which  usually  is 
some  form  of  cell,  on  the  walls  of 
which  nerves  are  distributed,  in- 
closing a  gelatinous  substance, 
the  whole  being  very  suggestive 
of  a  galvanic  battery)  closely  re- 
sembles a  muscle-nerve  prepara- 
tion or  its  equivalent  in  the  nor- 
mal body.  The  electric  organs  ex- 
perience fatigue  ;  have  a  latent 
period;  their  discharge  is  tetanic 
(interrupted)  ;  is  excited  by  me- 
chanical, thermal,  or  electrical 
stimuli ;  and  the  effectiveness  of 
the  organs  is  heightened  by  elevation  of  temperature,  and  the 
reverse  by  cooling,  etc. 


Fig.  192.— The  electric  -  fish  torpedo,  dis- 
sected to  show  electric  apparatus 
(Huxley),  h,  branchiae  ;  c,  brain  ;  e, 
electric  organ;  </.  cranium;  me,  spinal 
cord  ;  n.  nerves  to  jiectoral  fins ;  nl, 
nervi  laterales;  np.  branches  of  pneu- 
mogastric  nerves  to  electric  organs  ; 
o,  eye. 


Muscular  Work. 

If  during  a  given  peri(xl  one  of  two  persons  raises  a  weight 
through  the  same  height  but  twice  as  frequently  as  the  other, 
it  is  plain  that  he  does  twice  the  work ;  from  such  a  case  we 
may  deduce  tlie  rule  f(jr  calculating  work,  viz.,  to  multiply  the 
weight  and  height  together. 


200 


ANIMAL  PHYSIOLOGY. 


The  effectiveness  of  a  given  muscle  must,  of  course,  depend 
on  the  degree  to  which  it  shortens,  which  is  from  one  half  to 
three  fifths  of  its  length ;  and  the  number  of  fibers  it  contains 

i.  e.,  upon  its  length  and  the  area  of  its  cross-section,  taking 

into  account  in  connection  with  the  first  factor  the  arrange- 
ment of  the  fibers;  those  muscles  in  which  the  fibers  run 
longitudinally  being  capable  of  the  greatest  total  shortening. 

There  is,  as  shown  by  actual  experimental  trial,  a  relation 
between  the  work  done  and  the  load  to  be  lifted.  With  double 
the  weight  the  contraction  may  be  as  great  as  at  first,  or  even 
greater ;  but  a  limit  is  soon  reached  beyond  which  contraction 
is  impossible.  This  principle  may  be  stated  thus :  Tlie  contrac- 
tion is  a  function  of  the  stimulus,  and  is  illustrated  by  the 
diagram  below  (Fig.  193), 


T'TTT  r  I  ]  TTT-T-r-1 


3: 


^0        10        20        30        40        43        50        55       60        (55       70        75       80        90      100 

Fig.  193. — Diagram  of  muscular  contractions  with  same  stimulus  and  increasing  weights.    The 
numbers  represent  grammes  (McKendrick). 

It  has  been  shown  experimentally  that  the  chemical  inter- 
changes in  a  muscle,  acting  against  a  considerable  resistance, 
are  increased — i.  e.,  the  metabolism  and  the  working  tension  are 
related. 

These  experimental  facts  harmonize  with  our  experience 
of  a  sense  of  satisfaction  and  effectiveness  in  the  use  of  the 
muscles  when  weights  are  held  in  the  hands ;  and  it  must  be  a 
matter  of  practical  importance  that  each  person  should,  in 
taking  systematic  exercise,  keep  to  that  kind  which  does  not 
either  overweight  or  underweight  the  muscles. 

Circumstances  influencing  the  Character  of  Muscular 
AND  Nervous  Activity. 

The  Influence  of  Blood-Supply.  Fatigue. — Fig.  194  shows  at  a 
glance  differences  in  the  curves  made  by  a  contracting  muscle 
suffering  from  increasing  fatigue. 

Suppose  that  in  such  a  case  the  blood  had  been  withheld 
from  the  muscle,  and  that  it  is  now  admitted,  an  almost  im- 
mediate effect  is  seen  in  the  nature  of  the  contractions ;  but 
even  if  only  saline  solution  had  been  sent  through  the  vessels 
of  the  muscle,  a  similar  change  would  have  been  noticeable. 
We  may  fairly  conclude  that  the  blood  and  saline  removed 
something  which  had  been  exercising  a  depressing  effect  on  the 


APPLICATIONS   OF  THE   GRAPHIC    METHODo 


201 


vitality  of  the  muscle.     In  a  working  muscle,  like  all  living 
tissues,  there  are  products  of  vital  action  (metabolism)  tliat  are 


180  DV. 


Fig.  194.— Curves  of  a  muscle  contraction  in  different  stages  of  fatigue  (after  Yeo).  A,  curve 
when  muscle  wa.s  fresh  :  B,  C,  D,  E.  each  .iust  after  muscle  had  alreadj'  contracted  two 
hundred  times.  The  alteration  in  length  of  latent  period  is  not  well  brought  out  in  these 
tracings. 

poisonous.  We  have  already  learned  that  a  working  muscle 
generates  an  excess  of  carbonic  anhydride,  and  something  which 
gives  it  an  acid  reaction ;  and  that  it  uses  up  oxygen  as  well  as 
other  matters  derivable  from  blood. 

Fatigue  will  occur,  it  is  well  known,  if  the  muscles  are  used 
for  an  indefinitely  long  period,  no  matter  how  favorable  the 
blood-supply — another  evidence  that  there  is,  in  all  probability, 
some  chemical  product,  the  result  of  their  own  activity,  depress- 
ing them ;  and  this  is  rendered  all  the  more  likely  when  it  is 
learned  that  the  injection  of  lactic  acid,  to  take  one  example, 
produces  effects  like  ordinary  fatigue. 

It  is  also  a  matter  of  common  exj^erience  that  exercise,  while 
beneficial  to  the  whole  body,  the  muscles  included,  as  shown  by 
their  enlargement  under  it,  becomes  injurious  when  carried  to 
the  point  of  fatigue. 

Why  the  use  of  the  muscles  is  conducive  to  their  welfare  is 
but  a  part  of  a  larger  question.  Why  does  the  use  of  any  tissue 
improve  it  ? 

When  the  nerve  which  supplies  a  muscle  is  stimulated  its 
blood-vessels  dilate,  and  it  has  been  assumed  that  the  same 
happens  when  a  muscle  contracts  normally  in  the  body ;  and 
when  muscular  action  is  increased  there  is  a  corresponding 
augmentation  in  tlie  quantity  of  blood  driven  through  the 
muscles  in  a  given  period,  even  if  there  be  no  actual  increase 
in  the  caliber  of  the  blood-vessels,  for  the  heart-beat  is  greatly 
accelerated. 

But  repose  is  as  necessary  as  exercise  for  the  greatest  effect- 
iveness of  the  muscles,  as  the  experience  of  all,  and  especially 
athletes,  ])rov<'s. 

That  the  nervous  system  plays  a  great  part  in  the  nutrition 
of  muscles  is  evident  from  the  fact,  among  countless  others, 
tliat  it  is  not  possible  to  use  the  brain  to  its  greatest  ca])acity 
and  tlie  muscles  to  their  fullest  at  the  same  time ;  the  individual 


202  ANIMAL   PHYSIOLOGY, 

engaged  in  physical  "  training  "  must  forego  severe  mental  ap- 
plication. Nervous  energy  is  required  for  the  muscles,  and  all 
questions  of  blood-supply  are,  though  important,  subordinate. 
But  it  would  be  premature  to  enter  into  a  full  discussion  of  this 
interesting  topic  now. 

The  sense  of  fatigue  experienced  after  prolonged  muscular 
action  is  complex,  though  there  can  be  no  doubt  that  the  nerve- 
centers  must  be  taken  into  account,  since  any  muscular  work 
that,  from  being  unusual,  requires  closer  attention  and  a  more 
direct  influence  of  the  will,  is  well  known  to  be  more  fatiguing. 
On  the  other  hand,  the  accumulation  of  products  of  fatigue 
doubtless  reports  itself  through  the  local  nervous  mechanism. 

Separation  of  Muscle  from  the  Central  Nervous  System. — When 
the  nerve  belonging  to  a  muscle  is  divided,  certain  histological 
changes  ensue,  which  may  be  briefly  described  as  fatty  degenera- 
tion, followed  by  absorption ;  and  when  regeneration  of  the 
nerve-fibers  takes  place  on  apposition  of  the  cut  ends,  a  more 
or  less  complete  restoration  of  the  functions  of  the  nerve  fol- 
lows, but  the  exact  nature  of  the  process  of  repair  is  not  yet 
fully  agreed  upon ;  it  seems,  in  fact,  to  vary  in  different  cases 
as  to  details,  though  it  is  likely  that,  in  instances  in  which 
there  is  a  complete  return  to  the  normal  functionally,  the  axis- 
cylinders,  at  all  events,  are  reproduced. 

The  degeneration  downward  is  complete ;  upward,  only  to 
the  first  node  of  Ranvier. 

Immediately  after  the  section  the  irritability  of  the  nerve  is 
increased,  but  rapidly  disappears,  from  the  center  toward  the 
periphery  (Ritter-Valli  law). 

In  the  mean  time  the  muscle  has  been  suffering.  Its  irrita- 
bility at  first  diminishes,  then  becomes  greater  than  usual  to 
shocks  from  the  make  or  break  of  the  constant  current ;  but 
finally  all  irritability  is  lost,  and  fatty  degeneration  and  disap- 
pearance of  true  muscular  structure  complete  the  history.  It 
is  theoretically  interesting,  as  well  as  of  practical  importance, 
that  degeneration  may  be  delayed  by  the  use  of  the  constant 
current,  the  significance  of  which  we  have  already  endeavored 
to  explain. 

The  Influence  of  Temperature. — If  a  decapitated  frog  be  placed 
in  water  of  the  ordinary  temperature,  and  heat  be  gradually 
applied,  the  animal  does  not  move  (proving  that  the  spinal  cord 
alone  is  not  conscious),  but  the  muscles,  when  43°  to  50°  C.  is 
reached,  contract  and  become  rigid,  a  condition  known  as  "  heat- 
riaror." 


APPLICATIONS  OF  THE   GRAPHIC   METHOD.  203 

There  are  some  advantages  in  investigating  changes  in  tem- 
perature by  the  graphic  method.  Curves  from  a  muscle-nerve 
preparation  show  that  elevation  of  temperature  shortens  the 
latent  period  and  the  curve  of  contraction.  Lowering  the  tem- 
perature has  an  effect  exactly  opposite,  as  might  be  supposed, 
and  these  changes  take  place  in  the  muscles  of  both  cold-blooded 
and  warm-blooded  animals,  though  more  marked  in  the  latter. 

The  modifications  evident  to  the  eye  are  accompanied  by 
others,  chemical  in  nature,  and  a  comparison  of  these  shows 
that  the  rapidity  and  force  of  the  muscular  contraction  run 
parallel  with  the  rapidity  and  extent  of  the  chemical  changes. 

Certain  drugs  also  modify  the  form  of  the  muscle-curve  very 
greatly,  so  that  it  appears  that  the  molecular  action  which  un- 
derlies all  the  phenomena  of  muscle  and  nerve  (for  what  has 
been  said  of  muscle  applies  also  to  nerve,  if  we  substitute 
nervous  impulse  for  contraction)  can  go  on  only  within  those 
narrow  bounds  which,  one  realizes  more  and  more  in  the  study 
of  physiology,  are  set  to  the  activities  of  living  things. 

What  is  the  Intimate  Nature  of  Muscular  and  Nervous  Action  ? — 
The  answers  to  these  questions,  to  which  some  allusion  has  been 
already  made,  are  by  no  means  certain.  Some  believe  that, 
since  the  nitrogeneous  waste  of  the  body,  if  judged  by  the  urea 
of  the  urine,  is  not  augmented,  some  carbohydrate  breaks  up, 
which  would  be  in  accord  with  the  fact  that  the  gaseous  inter- 
change of  the  body  generally  is  increased  during  exercise,  espe- 
cially the  excretion  of  carbonic  anhydride. 

Upon  the  whole,  however,  such  a  view  does  not  harmonize 
well  with  the  behavior  of  protoplasm  generally,  and  it  is  possi- 
ble to  conceive  of  other  processes  which  would  give  rise  to  car- 
bonic anhydride  and  additional  waste  products. 

It  seems  to  be  likely  that  the  muscle  protoplasm  builds  up 
and  breaks  down  as  a  whole  ;  that  this  is  constantly  going  on ; 
and  that  the  oxygen  which  is  stored,  away  (intra-molecular) 
suffices  for  immediate  use ;  but  that  when  a  contraction  takes 
place  all  the  chemical  processes  are  heightened,  so  that  we 
may  conceive  most  naturally  of  the  various  aspects  of  muscular 
life  as  phases  of  a  whole,  the  parts  of  wliich  are  closely  linked 
together. 

Another  unsettled  point  is  the  explanation  of  the  fact  tliat 
a  nerve,  when  stimulated  nearer  the  nerve-center,  gives  rise  to  a 
more  marked  contraction,  with  the  same  stimulus  than  when 
excited  neanjr  the  muscle. 

Some  suppose  that  the  change  that  in  a  nerve  constitutes  an 


204  ANIMAL  PHYSIOLOGY, 

impulse  gathers  force  as  it  proceeds — tlie  avalanche  theory  of 
Pflliger  ;  but  it  would  seem  more  natural  to  refer  this  effect  to 
the  greater  irritability  of  the  nerve  nearer  the  centers. 

The  chemistry  of  dead  nerves  throws  extremely  little  light 
on  the  nature  of  nervous  processes.  The  latter  seem,  in  fact, 
to  be  accompanied  by  chemical  changes  which  almost  entirely 
elude  our  methods  of  detection  and  estimation.  Relatively  to 
the  chemical  the  electrical  phenomena  are  predominant;  but 
nerve-force  is  not  electrical  force,  nor  are  we  prepared  yet  to 
teach  that  it  is  the  equivalent  of  that  or  any  other  force  known 
to  us. 

The  fact  that  a  nerve  maintained  in  a  condition  approxi- 
mately normal  may  be  stimulated  for  hours  without  exhaus- 
tion, has  led  some  to  adopt  the  tempting  conclusion  that  there 
are  no  invariable  chemical  accompaniments  of  nervous  excita- 
tion. But  in  this  and  all  other  instances  we  think  that  general 
principles  must  not  be  readily  set  aside  by  special  cases,  and 
we  should  ourselves  hesitate  to  adopt  any  opinion  so  contrary 
to  all  that  is  known  of  organic  processes  as  this  theory  implies, 
except  on  the  amplest  and  clearest  evidence ;  and  we  lay  the 
more  stress  on  this,  because  we  think  it  is  a  sample  of  the  sort 
of  reasoning  that  is  apt  to  become  over -potent  with  those  that 
derive  their  conclusions  wholly  or  chiefly  from  laboratory  ex- 
periments, to  the  neglect  of  wider  observations,  which  put  the 
more  limited,  and  possibly  more  accurate,  ones  derived  from 
the  former  source,  in  a  truer  light,  and  enable  us  to  establish 
juster  relations. 

Unstkiped  Muscle. 

This  form  of  muscular  tissue  is  characterized  by  its  long 
latent  period,  its  slow  wave  of  contraction,  its  not  passing  into 
tetanus,  and  the  progress  of  the  contraction  being  in  either  a 
transverse  or  longitudinal  direction,  a  wave  of  contraction  in 
one  cell  being  capable  of  setting  up  a  corresponding  wave  in 
adjoining  cells  even  when  no  nerve-fibers  are  distributed  to 
them.  It  is  excited,  though  less  readily,  by  all  the  kinds  of 
stimuli  that  act  upon  striped  muscle.  In  the  higher  groups  of 
animals  this  tissue  is  chiefly  confined  to  the  viscera  of  the 
chest  and  abdomen,  constituting  in  the  case  of  some  of  them 
the  greater  part  of  the  whole  organ. 

The  slow  but  powerful  and  rhythmical  contraction  of  this 
form  of  muscle  adapts  it  well  to  the  part  such  organs  play  in 


APPLICATIONS  OF  THE   GRAPHIC   METHOD.  205 

the  economy.  There  are  variations,  however,  in  the  rapidity, 
force,  regularity,  and  other  qualities  of  the  contraction  in  dif- 
ferent parts :  thus,  it  is  comi^aratively  rapid  in  the  iris,  and  ex- 
tremely powerful  and  regular  in  the  uterus,  serving  to  produce 
that  prolonged  yet  intermittent  pressure  essential  under  the 
circumstances  (expulsion  of  the  foetus). 

Comparative. — Muscular  contraction  is  relatively  sluggish 
and  prolonged  among  the  invertebrates,  to  which,  however,  the 
movement  of  the  wings  of  insects  is  a  marked  exception,  some 
of  them  having  been  shown  by  the  graphic  method  to  vibrate 
some  hundreds  of  times  in  a  second. 

The  slow  movements  of  the  snail  are  proverbial.  As  a  rule, 
the  strength  of  the  muscles  of  the  invertebrates  is  incomparably 
greater  than  that  of  vertebrates,  as  witness  the  powerful  grasp 
of  a  crab's  claw  or  a  beetle's  jaws. 

These  facts  are  in  harmony  with  the  generally  slow  metab- 
olism of  most  invertebrates  and  the  lower  vertebrates. 

The  muscles  of  the  tortoise  contract  tardily  but  with  great 
power,  resist  fatigue  well,  retain  their  vitality  under  unfavor- 
able conditions,  and  after  death  for  a  very  long  period  (days). 

Without  resorting  to  elaborate  experiments,  the  student 
may  convince  himself  of  the  truth  of  most  of  the  above  state- 
ments by  observing  the  movements  of  a  water-snail  attached 
to  a  glass  vessel ;  the  note  made  by  the  buzzing  of  an  insect, 
and  comparing  it  with  one  approaching  it  in  pitch  sounded  by 
some  instrument  of  music ;  the  force  necessary  to  withdraw 
the  foot  or  tail  of  a  tortoise ;  the  peristaltic  movements  of  the 
intestine  and  other  organs  in  a  freshly  killed  animal ;  or  the 
action  of  a  bee,  wasp,  or  wood-boring  beetle  on  the  cork  of  a 
bottle  in  which  one  of  them  may  be  inclosed. 

Special  Considerations. 

In  the  case  of  weakly  (phthisical)  persons  a  sharp  tap  on 
the  chest  will  often  j^roduce  a  contraction  of  the  muscles  thus 
stimulated ;  but,  in  addition,  a  local  contraction  lasting  some 
little  time,  known  as  a  ivheal  or  idio-muscular  contraction,  fol- 
lows. This  phenomenon  seems  to  be  the  result  of  a  special 
irritability  in  such  muscles. 

Cramp  may  arise  under  a  great  variety  of  circumstances, 
hut  it  seems  to  be  in  all  cases  either  a  complete  prolonged  teta- 
nus, in  which  then^  is  unusual  muscular  shortening  in  severe 
cases,  at  least,  or  the  persistence  of  a  contraction  remainder. 


206  ANIMAL   PHYSIOLOGY. 

The  great  differences  known  to  exist  between  individuals  of 
tlie  same  species  in  strength,  endurance,  fleetness,  and  other 
particulars  in  which  the  muscles  are  concerned,  raise  numer- 
ous interesting  inquiries.  The  build  of  the  greyhound  or  race- 
horse suggests  in  itself  part  of  the  explanation  on  mechanical 
principles,  lung  capacity,  etc.  But  when  it  is  found  that  one 
dog,  horse,  deer,  or  man  excels  another  of  the  same  race  in 
swiftness  or  endurance,  and  there  is  nothing  in  the  form  to 
furnish  a  solution,  we  are  prompted  to  ask  whether  the  muscles 
may  not  contract  more  energetically,  experience  a  shortening 
of  the  latent  period,  or  other  phase  of  contraction;  or  whether 
they  produce  less  of  waste-products  or  get  rid  of  them  more 
rapidly.  The  whole  subject  is  extremely  complicated,  and  we 
may  say  here  that  there  is  some  evidence  to  show  that  in  races 
of  dogs  and  other  animals  which  surpass  their  fellows,  the 
nerve  regulating  the  heart  and  lungs  (vagus)  has  greater  power ; 
but,  leaving  this  and  much  more  out  of  the  account,  it  is  likely 
there  are  individual  differences  in  the  functional  nature  of  the 
muscle.  Of  equal  or  more  importance  is  the  energizing  influ- 
ence of  the  nervous  system,  which  probably  under  great  excite- 
ment (public  boat-races,  etc.)  acts  to  produce  in  man  those 
supermaximal  contractions  which  seem  to  leave  the  muscle 
long  the  worse  of  its  unusual  action.  The  nerve-centers,  it  is 
likely,  suffer  still  more  from  excessive  discharge  of  nerve-force 
(as  we  may  speak  of  it  for  the  present)  necessary  to  originate 
the  muscular  work.  Hence  the  importance  of  training  to 
minimize  the  non-effective  expenditure,  ascertain  the  capacity 
possessed,  learn  the  direction  in  which  weaknesses  lie ;  and 
equally  important  the  much-neglected  period  of  rest  before 
actual  contests — if  such  are  to  be  undertaken  at  all — so  that 
all  the  activities  of  the  body  may  gather  head,  and  thus  be 
prepared  to  meet  the  unusual  demand  upon  them. 

The  law  of  rhythm  in  organic  nature  is  beautifully  illus- 
trated by  the  behavior  of  nerve  and  especially  muscle ;  at  least 
it  is  more  obvious  in  the  case  of  muscle,  at  this  stage  of  our 
progress. 

The  regularity  with  which  one  phase  succeeds  another  in  a 
single  contraction ;  the  essentially  rhythmic  (vibratory)  char- 
acter of  tetanus,  fatigue  and  recovery ;  the  recurrence  of  in- 
crease and  decrease  in  the  muscle  and  nerve  currents — in  fact, 
the  whole  history  of  muscle  is  an  admirable  commentary  on 
the  truth  of  the  law  of  rhythm,  into  which  in  further  detail 
space  will  not  permit  us  to  enter. 


APPLICATIONS   OP   THE  GRAPHIC   METHOD.  207 

It  is  a  remarkable  fact  that  the  endurance  of  man,  especially 
civilized  man,  seems  to  be  greater  than  that  of  any  other  mam- 
mal. It  may  be  hazardous  to  express  a  dogmatic  opinion  as  to 
the  reason  of  this,  but  the  influence  of  the  mind  over  the  body 
is  unquestionably  greater  in  man  than  in  any  other  animal ; 
and,  if  we  are  correct  in  assigning  so  much  importance  to  the 
influence  of  the  nervous  system  in  maintaining  the  proper 
molecular  balance  which  is  at  the  foundation  of  the  highest 
good  of  an  organism,  we  certainly  think  that  it  is  in  this  direc- 
tion we  must  look  for  the  explanation  of  the  above-mentioned 
fact,  and  much  more  that  would  otherwise  be  obscure  in  man's 
functional  life. 

Functional  Variations. — We  have  endeavored,  in  treating  this 
subject  of  muscle,  to  point  out  how  the  phenomena  vary  with 
the  animal,  the  kind  of  muscle,  and  the  circumstances  under 
which  they  are  manifested.  It  may  be  shown  that  every  one 
of  the  qualities  which  a  muscle  possesses,  varies  with  the  tem- 
perature, the  blood-supply,  the  duration  of  its  action,  the  char- 
acter of  the  stimulus,  and  other  modifying  agents.  Not  only 
are  there  great  variations  for  different  groups  of  animals,  but 
lesser  ones  for  individuals ;  though  the  latter  are  made  more 
evident  indirectly  than  when  tested  by  the  usual  laboratory 
methods ;  but  they  must  be  taken  account  of  if  we  would  un- 
derstand animals  as  they  are.  Some  of  these  will  be  referred 
to  later. 

If  a  muscle-cell  be  regarded  in  the  aspect  that  we  are  now 
emphasizing,  its  study  will  tend  to  impress  those  fundamental 
biological  laws,  the  comprehension  of  which  is  of  more  impor- 
tance than  the  acquisition  of  any  number  of  facts,  which,  how- 
ever interesting,  can,  when  isolated,  profit  little. 

Experiment  has  not  done  much  directly,  and  it  seems  can 
not  at  present,  for  the  physiology  of  man,  though  more  may  be 
accomplished  as  regards  muscle  and  nerve  than  some  other 
tissues.  It  is,  of  course,  possible  to  measure  the  rai)idity  of 
the  i>assage  of  a  nervous  impulse  and  to  study  electrical  phe- 
nomena generally  to  some  extent.  Putting  all  that  is  known 
together,  it  would  appear  that,  without  referring  to  minor  dif- 
ferences which  unquestionably  exist,  the  muscle  and  nerve 
physiology  of  man  corresponds  pretty  closely  with  that  of  one 
of  the  highest  mammals,  and,  as  compared  with  the  lower  ver- 
tebrates, his  muscles  and  nerves  possess  an  irritability  of  a 
very  exalted  type,  with,  however,  a  corresponding  loss  or  dif- 
ference in  other  directions. 


208  ANIMAL   PHYSIOLOGY. 

Summary  of  the  Physiology  of  Muscle  and  Nerve. — The  move- 
ments of  a  muscle  are  distinguished  from  those  of  other  forms 
of  protoplasm  by  their  marked  definiteness  and  limitation. 

The  contraction  of  a  muscle-fiber  (cell)  results  in  an  increase 
in  its  short  transverse  diameter,  and  a  diminution  of  its  long 
diameter,  without  appreciable  change  in  its  total  bulk. 

Muscle  and  nerve  are  not  automatic,  but  are  irritable. 
Though  muscle  normally  receives  its  stimulus  through  a  nerve, 
it  possesses  independent  irritability. 

Stimuli  may  be  mechanical,  chemical,  thermal,  electrical,  and 
in  the  case  of  muscle,  nervous ;  and  to  be  effective  they  must 
be  applied  suddenly  and  last  for  a  brief  but  appreciable  time. 

Electrical  stimulation,  especially,  is  only  effective  when 
there  is  a  sudden  change  in  the  force  or  direction  of  the  cur- 
rents.    This  applies  to  both  muscle  and  nerve. 

A  muscular  contraction  consists  of  three  phases :  the  latent 
period,  the  period  of  rising,  and  the  period  of  falling  energy, 
or  of  contraction  and  relaxation. 

When  the  phase  of  relaxation  is  minimal  and  that  of  con- 
traction approaches  continuity,  a  tetanus  results.  The  contrac- 
tions of  the  muscles  in  situ  are  tetanic,  and  are  accompanied 
by  a  low  sound,  evidence  in  itself  of  their  vibratory  character. 

The  prolonged  contraction  of  a  muscle  leads  to  fatigue; 
owing  in  part,  at  least,  to  the  accumulation  of  waste-products 
within  the  muscle  which  depress  its  energies. 

This  is  a  necessary  consequence  of  the  fact  that  all  proto- 
plasmic activity  is  accompanied  by  chemical  change,  and  that 
some  of  these  processes  result  in  the  formation  of  products 
which  are  hurtful  and  are  usually  rapidly  expelled. 

Muscular  contraction  is  accompanied  by  chemical  changes, 
in  which  the  formation  of  carbon  dioxide,  and  some  substance 
that  causes  an  acid  reaction  to  take  the  place  of  an  alkaline  or 
neutral  one.  Since  free  oxygen  is  not  required  for  the  act  of 
contraction,  but  is  still  used  up  by  a  contracting  muscle,  it  may 
be  assumed  that  the  oxygen  that  plays  a  part  in  actual  con- 
traction is  intra-molecular. 

Chemical  changes  are  inseparable  from  the  vital  processes 
of  all  protoplasm,  and  the  phenomena  of  muscle  show  that 
they  are  constantly  in  operation,  but  exalted  during  ordinary 
contraction  and  that  tetanic  condition  which  precedes  and 
may  end  in  coagulation  of  muscle  plasma  and  the  formation  of 
myosin.  The  latter  is  a  result  of  the  disorganization  of  muscle, 
and  has  points  of  resemblance  to  the  coagulation  of  the  blood. 


APPLICATIONS  OF  THE  GRAPHIC  METHOD.  209 

The  contraction  of  a  muscle,  and  the  passage  of  a  nervous 
impulse,  are  accompanied  by  electrical  changes.  Whether  cur- 
rents exist  in  uninjured  muscle  and  nerve  is  a  matter  of  con- 
troversy. All  physiologists  agree  that  they  exist  in  muscle 
(and  nerve)  during  functional  activity.  This  electrical  condi- 
tion is  termed  the  "  negative  variation  "  by  those  believing  in 
currents  of  rest,  and  the  "  current  of  action  "  by  those  holding 
opposite  opinions.  The  current  is  of  momentary  duration,  and 
is  manifested  during  the  latent  period  of  muscle,  in  which  also 
the  chemical  changes  take  place ;  so  that  a  muscular  contrac- 
tion must  be  regarded  as  the  outcome  of  the  events  of  the 
latent  period,  which  is,  therefore,  tliough  the  shortest,  the  most 
important  of  the  phases  of  a  muscular  contraction. 

During  the  passage  of  a  constant  (polarizing)  current  from 
a  battery  through  a  nerve,  it  undergoes  a  change  in  its  irrita- 
bility and  shows  a  variation  in  the  electro-motive  force  of  the 
ordinary  nerve-current  (electrotonus).  This  fact  is  of  thera- 
peutic importance.  The  electrical  phenomena  of  nerve  are  alto- 
gether more  prominent  than  the  chemical,  the  reverse  of  which 
is  true  of  muscle.  The  activity  of  a  muscle  (and  nerve  proba- 
bly) is  accompanied  by  the  generation  of  heat,  an  exaltation  of 
which  takes  place  during  muscular  contraction. 

Rigor  mortis  causes  an  increase  in  temperature  and  the 
chemical  interchanges  which  accompany  the  other  phenomena. 
A  muscle  may  also  become  rigid  by  passing  into  rigor  caloris. 
Living  muscle  is  translucent,  alkaline  or  neutral  in  reaction, 
and  elastic ;  dead  muscle,  opaque,  acid  in  reaction,  and  devoid 
of  elasticity,  but  firmer  than  living  muscle,  owing  to  coagula- 
tion of  the  muscle-plasma.  Dead  nerve  undergoes  similar 
changes. 

The  elasticity  of  muscle  is  restricted  but  perfect  within  its 
own  limits.  It  differs  from  that  of  inorganic  bodies  in  that  the 
increments  of  extension  are  not  directly  proportional  to  the  in- 
crements of  the  weight.  When  overstretched,  muscle  does  not 
return  to  its  original  length  (loss  of  elasticity),  lience  the  serious 
nature  of  sprains. 

It  is  important  to  regard  muscular  elasticity  as  an  expres- 
sion of  vital  properties. 

The  work  done  by  a  muscle  is  ascertained  by  multiplying 
the  load  lifted  by  the  height;  and  the  capacity  of  an  individual 
muscle  will  vary  with  its  hiugth,  the  arrangement  of  its  libers, 
and  the  area  of  its  cross-secti(jn  (i.  e.,  on  the  number  of  fibers). 

The  work  done  may  be  regarded  as  a  function  of  the  resist- 

14 


210  ANIMAL  PHYSIOLOGY. 

ance  (load)^  as  the  contraction  is  also  a  function  of  the  stimulus. 
The  separation  of  a  muscle  from  its  nerve  by  section  of  the  lat- 
ter leads  to  certain  changes^  most  rapid  in  the  nerve;,  which 
show  that  the  two  are  so  related  that  prolonged  independent 
vitality  of  the  muscle  is  impossible,  and  make  it  highly  proba- 
ble that  muscle  is  constantly  receiving  some  beneficial  stimulus 
from  nerve^  which  is  exalted  and  manifest  when  contraction 
takes  place. 

The  study  of  the  development  of  the  electrical  cells  of  cer- 
tain fishes  shows  that  they  are  greatly  modified  muscles  in 
which  contractility,  etc.,  has  been  exchanged  for  a  very  decided 
exaltation  of  electrical  properties.  It  is  likely,  though  not 
demonstrated,  that  all  forms  of  protoplasm  undergo  electrical 
changes — that  these,  in  fact,  like  chemical  phenomena,  are  vital 
constants. 

The  phases  of  the  contraction  of  smooth  muscular  tissue  are 
all  of  longer  duration ;  the  contraction- wave  passes  in  different 
directions,  and  may  spread  into  cells  devoid  of  nerves,  which 
we  think  not  unlikely  also  to  be  the  case,  though  less  so,  for  all 
forms  of  muscle. 

The  smooth  muscle-cell  must  be  regarded  as  a  more  primi- 
tive, less  specialized,  form  of  tissue.  Variations  in  all  the  phe- 
nomena of  muscle  with  the  animal  and  the  circumstances  are 
clear  and  impressive.  Finally,  muscle  illustrates  an  evolution 
of  structure  and  function,  and  the  law  of  rhythm. 


THE  NEEVOUS  SYSTEM.— GENERAL  CONSIDERATIONS. 

Since  in  the  higher  vertebrates  the  nervous  system  is  domi- 
nant, regulating  apparently  every  process  in  the  organism,  it 
will  be  well  before  proceeding  further  to  treat  of  some  of  its 
functions  in  a  general  way  to  a  greater  extent  than  we  have  yet 
done. 

Manifestly  it  must  be  highly  important  that  an  animal  shall 
be  able  to  place  itself  so  in  relation  to  its  surroundings  that  it 
may  adapt  itself  to  them.  Prominent  among  these  adaptations 
are  certain  movements  by  which  food  is  secured  and  dangers 
avoided.  The  movements  having  a  central  origin,  a  peripheral 
mechanism  of  some  kind  must  exist  so  as  to  place  the  centers 
in  connection  with  the  outer  world.  Passing  by  the  evolution 
of  the  nervous  system  for  the  present,  it  is  found  that  in  verte- 
brates generally  there  is  externally  a  modification  of  the  epi- 


THE  NERVOUS  SYSTEM— GENERAL   CONSIDERATIONS.      211 

thelial  covering  of  the  body  (end-organ)  iu  wliich  a  nerve  ter- 
minates, which  latter  may  be  traced  to  a  cell  or  cells  removed 
from  the  surface  [cenier),  and  from  which  in  most  cases  other 
nerves  proceed. 

The  nervous  system,  we  may  remind  the  student,  consists  in 
vertebrates  of  centers  in  which  nerve-cells  abound,  united  by 
nerve-fibers  and  by  the  most  delicate  form  of  connective  tissue 
known,  in  connection  with  which  there  are  incased  strands  of 
protoplasm  or  nerves  as  outgrowths.  The  main  centers  are,  of 
course,  aggregated  in  the  brain  and  spinal  cord. 

It  is  possible  to  conceive  of  the  work  of  a  nervous  system 
carried  on  by  a  single  cell  and  an  afferent  and  efferent  nerve ; 
but  inasmuch  as  such  an  arrangement  would  imply  that  the 
central  cell  should  act  the  part  of  both  receiving  and  origi- 
nating impulses  (except  it  were  a  mere  conductor,  in  which  case 
there  would  be  no  advantage  whatever  in  the  existence  of  a  cell 
at  all),  according  to  the  principle  of  the  physiological  division 
of  labor,  we  might  expect  that  there  would  be  at  least  two  cen- 
tral cells — one  to  receive  and  the  other  to  transmit  impulses — 
or  at  least  that  there  should  be  some  specialization  among  the 
central  cells ;  and  we  shall  have  good  reason  later  to  believe 
that  this  has  reached  a  surprising  degree  in  the  highest  ani- 
mals. 

Moreover^  it  would  be  a  great  advantage  if  the  termination 
of  the  ingoing  (afferent)  nerve  should  not  lie  exposed  on  the 
surface,  but  be  protected  by  some  form  of  cell  that  had  also  the 
power  to  transmit  to  it  the  impressions  received  from  without, 
in  a  form  suitable  to  the  nature  of  the  nerve  and  the  needs  of 
the  organism. 

So  that  a  complete  mechanism  in  its  simplest  form  would 
furnish :  1.  A  peripheral  cell  or  nerve  end-organ.  3.  An  affer- 
ent or  sensory  nerve.  3.  Two  or  more  central  cells.  4.  An 
efferent  nerve,  usually  connected  with — 5.  A  muscle  or  other 
form  of  cell,  the  action  of  which  may  be  modified  by  the  out- 
going nerve,  or,  as  we  should  prefer  to  say,  by  the  central  nerv- 
ous cells  through  the  efferent  nerve.  The  advantages  of  the 
principal  cells  being  within  and  protected  are  obvious. 

When,  then,  an  im^jression  made  on  the  perifjlieral  cell  is 
carrie<l  inward,  there  modified,  and  results  in  an  outgoing  nerv- 
ous impulse  answering  to  tlie  afferent  one,  giving  rise  to  a  mus- 
cular contraction  or  other  effect  not  confined  to  the  recipient 
cells,  the  process  is  termed  reflex  action. 

The  great  size,  the  multiplicity  of  forms,  the  distinct  out- 


212     .  ANIMAL  PHYSIOLOGY. 

line  and  large  nuclei  of  nerve-cells,  suggest  the  probability 
that  they  play  a  very  important  part,  and  such  is  found  to  be 
the  case.  Indeed,  in  some  sense  the  rest  of  the  nervous  system 
may  be  said  to  exist  for  them. 

Probably  nerve-cells  do  sometimes  act  as  mere  conductors 
of  nervous  impulses  originating  elsewhere,  but  such  is  their 
lowest  function.  Accordingly,  it  is  found  that  the  nature  of 
any  reflex  action  depends  most  of  all  on  the  behavior  of  the 
central  cells. 

It  can  not  be  too  well  borne  in  mind  that  nerves  are  con- 
ductors and  such  only.     They  never  originate  impulses. 

The  properties  considered  in  the  last  chapter  are  common  to 
all  kinds  of  nerves  known ;  and  though  we  must  conceive  that 
there  are  some  differences  in  the  form  of  impulses,  these  are  to 
be  traced,  not  to  the  nerve  primarily,  but  to  the  organ  in  which 
it  ends  peripherally  or  to  the  central  cells. 

To  return  to  reflex  action,  it  is  found  that  the  muscular  re- 
sponse to  a  peripheral  irritation  varies  with  the  point  stimu- 
lated, the  intensity  of  the  stimulus,  etc.,  but  is,  above  all,  de- 
termined by  the  central  cells. 

Nerve  influence  may  be  considered  as  following  lines  of 
least  resistance,  and  there  is  much  evidence  to  show  that  an 
impulse  having  once  taken  a  certain  path,  it  is  easier  for  it  to 
pass  in  this  direction  a  second  time,  so  that  we  have  the  founda- 
tion of  the  laws  of  habit  and  a  host  of  interesting  phenomena 
in  this  simple  principle. 

It  is  found  that,  in  a  frog  deprived  of  its  brain  and  sus- 
pended by  the  under  jaw,  there  is  no  movement  unless  some 
stimulus  be  applied ;  but  if  this  be  done  under  suitable  condi- 
tions, instructive  results  follow,  which  we  now  proceed  to  indi- 
cate briefly.  The  experiments  are  of  a  simple  character,  which 
any  student  may  carry  out  for  himself. 

Experimental. — Preparing  a  frog  by  cutting  off  the  whole 
of  the  upper  jaw  and  brain-case  after  momentary  anaesthesia, 
suspend  the  animal  by  the  lower  jaw  and  wait  till  it  is  perfect- 
ly quiet.  Add  to  water  in  a  beaker  sulphuric  acid  till  it  tastes 
distinctly  but  not  strongly  sou'r,  to  be  used  as  a  stimulus.  1. 
Apply  a  small  piece  of  bibulous  paper,  moistened  with  the  acid, 
to  the  inner  part  of  the  thigh  of  the  animal.  The  leg  will  be 
drawn  up  and  the  paper  probably  removed.  Remove  the  paper 
and  cleanse  the  spot.  2.  Apply  a  similar  piece  of  paper  to  the 
middle  of  the  abdomen ;  one  or  both  legs  will  probably  be 
drawn  up,  and  wipe  off  the  offending  body.     3.  Let  the  foot  of 


THE   NERVOUS  SYSTEM— GENERAL  CONSIDERATIONS.      213 

the  frog  hang  in  the  liquid ;  after  a  few  moments  it  will  be 
withdrawn.  4.  Repeat,  holding  the  leg ;  probably  the  other  leg 
will  be  drawn  up.  5.  Apply  stronger  acid  to  the  inside  of  the 
right  thigh ;  the  whole  frog  may  be  convulsed,  or  the  left  leg 
may  be  put  in  action  after  the  right.  Even  if  the  stimulating 
paper  be  applied  near  the  anus,  it  will  be  removed  by  the  hind- 
legs.  6.  Beneath  the  skin  of  the  back  (posterior  lymph-sac) 
inject  a  few  drops  of  liquor  strychniae  of  the  pharmacopoeia ; 
after  a  few  minutes  apply  the  same  sort  of  stimulus  to  the 
thigh  as  before.      The  effects  follow  more  quickly  and   are 


bensory  centre 


INHIBITORY  CENTRE 


SENSORY  CELL  AND 
AFFERENT  NERVE 


Fio.  195.— Diagrram  intended  to  illustrate  nervous  mechanism  of— 1,  automatism;  2.  reflex 
action  :  and  '-i.  how  nervous  impulses  in  the  latter  case  may  pass  into  the  hif?her  parts  of 
brain  and  become  part  of  consciousness,  or  be  wholly  inhibited.  A  reflex  or  automatic 
center  may  for  the  sake  of  simplicity  be  reduced  to  a  single  cell,  as  above  on  the  left. 

much  more  marked — the  animal,  it  may  be,  passing  into  a  gen- 
eral tetanic  spasm. 

These  experiments  may  be  varied,  but  suffice  to  establish 
the  following  conclusions:  1.  The  stimulus  is  not  immediate- 
ly effective,  but  requires  to  act  for  a  certain  variable  period, 
depending  chiefly  on  the  condition  of  the  central  nervous  sys- 
tem. 2.  The  movements  of  the  muscles  harmonize  (are  co-ordi- 
nated), and  t(md  to  acconii)lish  some  end — are  purposive.     If 


214  ANIMAL  PHYSIOLOGY. 

the  nerve  alone  and  not  the  skin  be  stimulated,  there  may  be  a 
spasm  only  and  not  adaptive  movement,  3.  Nervous  impulses, 
when  very  abundant,  may  x^ass  along  unaccustomed  or  less  ac- 
customed paths  (experiments  4  and  5).  This  is  sometimes  spoken 
of  as  the  radiation  of  nervous  impulses. 

The  sixth  experiment  is  very  important,  for  it  shows  that 
the  result  varies  far  more  Avith  the  condition  of  the  nervous 
centers  (cells)  than  the  stimulus,  the  part  excited,  or  any  other 
factor. 

Automatism. — But,  seeing  that  these  central  cells  have  such 
independence  and  controlling  power,  the  question  arises.  Are 
these,  or  are  there  any  such  cells,  capable  of  originating  im- 
pulses in  nerves  wholly  independent  of  any  stimulus  from 
without  ?  In  other  words,  have  the  nerve-centers  any  true 
automatism  ?  Apparently  this  equality  is  manifested  by  uni- 
cellular organisms  of  the  rank  of  Amoeba.  Has  it  been  lost, 
or  has  it  become  a  special  characteristic  developed  to  a  high 
degree  in  nerve-cells  ? 

We  shall  present  the  facts  and  the  opinions  based  on  them 
as  held  by  the  majority  of  physiologists,  reserving  our  own 
criticisms  for  another  occasion :  1.  The  medulla  oblongata  is 
supposed  to  be  the  seat  of  numerous  small  groups  of  cells,  to  a 
large  extent  independent  of  each  other,  that  are  constantly 
sending  out  nervous  impulses  which,  proceeding  to  certain  sets 
of  muscles,  maintain  them  in  rhythmical  action.  One  of  the 
best  known  of  these  centers  is  the  respiratory.  2.  The  poste- 
rior lymph  hearts  of  the  frog  are  supplied  by  nerves  (tenth 
pair),  which  are  connected,  of  course,  with  the  spinal  cord. 
When  these  nerves  are  cut,  the  hearts  for  a  time  cease  to  beat, 
but  later  resume  their  action.  3.  The  heart  beats  after  all  its 
nerves  are  cut,  and  it  is  removed  from  the  body,  for  many  hours, 
in  cold-blooded  animals.  4.  The  contractions  of  the  intestine 
take  place  in  the  absence  of  food,  and  in  an  isolated  piece  of 
the  gut.  The  intestine,  it  will  be  remembered,  is  abundantly 
supplied  with  nerve-elements.  5.  In  a  portion  of  the  ureters, 
from  which  it  is  believed  nerve-cells  are  absent,  rhythmical 
action  takes  place. 

Conclusions.— 1.  Whether  the  action  of  the  respiratory  and 
similar  centers  could  continue  in  the  absence  of  all  stimuli  can 
not  be  considered  as  determined.  2.  That  there  are  regular 
rhythmical  discharges  from  the  spinal  nerve-cells  along  the 
nerves  to  the  lymph  hearts  seems  also  doubtful.  3.  Later  in- 
vestigations render  the  automaticity  of  the  heart  more  uncer- 


THE   XERVOUS  SYSTEM— GENERAL  CONSIDERATIONS.      215 

tain  than  ever,  so  that  the  result  stated  above  (3)  must  not  be 
interpreted  too  rigidly. 

Similar  doubts  hang  about  the  other  cases  of  apparent  au- 
tomatism. 

As  regards  the  various  comparatively  isolated  collections  of 
cells  known  as  ganglia,  the  evidence,  so  far  as  it  goes,  is  against 
their  possessing  either  automatic  or  reflex  action;  and  new 
views  of  their  nature  will  be  presented  in  due  course. 

Nervous  Inhibition.  —  If  the  pneumogastric  nerve  passing 
from  the  medulla  to  the  heart  of  vertebrates  be  divided  and 
the  lower  (peripheral)  end  stimulated,  a  decided  change  in  the 
action  of  the  heart  follows,  which  may  be  in  the  direction  of 
weakening  or  slowing,  or  positive  arrest  of  its  action. 

Assuming,  for  the  present,  that  the  cells  (center)  of  the  me- 
dulla have  the  power  to  bring  about  the  same  result,  it  is  seen 
that  such  nervous  influence  is  preventive  or  inhibitory  of  the 
normal  cardiac  beat,  so  that  the  vagus  is  termed  an  inhibitory 
nerve.  Such  inhibition  plays  a  very  important  part  in  the 
economy  of  the  higher  animals,  as  will  become  more  and  more 
evident  as  we  proceed.  The  nature  of  the  influences  that  pro- 
duce such  remarkable  results  will  be  discussed  when  we  treat 
of  the  heart. 

An  illustration  will  probably  serve  in  the  mean  time  to  make 
the  meaning  of  what  has  been  presented  in  this  chapter  more 
clear  and  readily  grasped. 

In  the  management  of  railroads  a  very  great  variety  of 
complicated  results  are  brought  about,  owing  to  system  and 
orderly  arrangement,  by  which  the  wishes  of  the  chief  mana- 
ger are  carried  out. 

Telegraphing  is  of  necessity  extensively  employed.  Sup- 
pose a  message  to  be  conveyed  from  one  office  to  another,  this 
may  (1)  simply  pass  through  an  intermediate  office,  without 
special  cognizance  from  the  operator  in  charge  ;  (2)  the  operator 
may  receive  and  transmit  it  unaltered  ;  (3)  he  may  be  required 
to  send  a  message  that  shall  vary  from  the  one  he  receives  in  a 
greater  or  less  degree  ;  or  (4)  he  may  arrest  the  command  alto- 
gether, owing  to  the  facts  which  he  alone  knows  and  upon 
which  he  is  empowered  always  to  act  according  to  his  best  dis- 
cretion. 

In  the  first  instance,  we  have  an  analogy  with  the  passage 
of  a  nervous  impulse  through  central  fibers,  or,  at  all  events, 
unafff'cted  by  colls;  in  the  secoiul,  the  resem})lance  is  to  cells 
acting  as  conductors  merely  ;  in  tin;  tliird,  t(j  the  usual  Ijehavior 


216  ANIMAL   PHYSIOLOGY. 

of  the  cells  in  reflex  action ;  and,  in  the  fourth,  we  have  an  in- 
stance of  inhibition.  The  latter  may  also  be  rendered  clear  by 
the  case  of  a  horse  and  its  rider.  The  horse  is  controlled  by  the 
rider,  who  may  be  compared  to  the  center,  through  the  reins 
answering  to  the  nerves,  though  it  is  not  possible  for  either  rider 
or  reins  to  originate  the  movements  of  the  animal,  except  as 
they  may  be  stimuli,  which  latter  are  only  effective  when  there 
are  suitable  conditions — when,  in  fact,  the  subject  is  irritable 
in  the  physiological  sense. 


THE  CIRCULATION  OF  THE  BLOOD. 

Every  tissue,  every  cell,  requiring  constant  nourishment, 
some  means  must  necessarily  have  been  provided  for  the  con- 
veyance of  the  blood  to  all  parts  of  the  organism.  We  now 
enter  upon  the  consideration  of  the  mechanisms  by  which  this 
is  accomplished  and  the  method  of  their  regulation. 

Let  us  consider  possible  mechanisms,  and  then  inquire  into 
their  defects  and  the  extent  to  which  they  are  found  embodied 
in  nature. 

That  there  must  be  a  central  pump  of  some  kind  is  evident. 
Assume  that  it  is  one-chambered,  and  with  an  outflow-pipe 
which  is  continued  to  form  an  inflow-pipe.  This  might  be  pro- 
vided with  valves  at  the  openings,  by  which  energy  would  be 
saved  by  the  prevention  of  regurgitation.  In  such  a  system 
things  must  go  from  bad  to  worse,  as  the  tissues,  by  constantly 
using  up  the  prepared  material  of  the  blood,  and  adding  to  it 
their  waste  products,  would  effect  their  own  gradual  starvation 
and  poisoning. 

It  might  be  conceived,  however,  that  waste  at  all  events  was 
got  rid  of  by  the  blood  being  conducted  through  some  elimi- 
nating organs ;  and  assume  that  one  such  at  least  is  set  aside 
for  respiratory  work.  If  the  blood  in  its  course  anywhere 
passed  through  such  organs,  the  end  would  be  attained  in  some 
degree  ;  but  if  the  division  of  labor  were  considerable,  we  should 
suppose  that,  gaseous  interchange  being  so  very  important  as 
we  have  been  led  to  see  from  the  study  of  the  chapters  on  gen- 
eral biology,  and  on  muscle,  organs  to  accomplish  this  work 
might  receive  the  blood  in  due  course  and  return  it  to  the  cen- 
tral pump  in  a  condition  eminently  fit  from  a  respiratory  point 
of  view. 

Such,  however,  would  necessarily  be  associated  with  a  more 


THE   CIRCULATION  OF  THE   BLOOD.  217 

complicated  pump :  and,  if  this  were  so  constructed  as  to  pre- 
vent the  mixture  of  blood  of  different  degrees  of  functional 
value,  higher  ends  would  be  attained. 

Turning  to  the  channels  themselves  in  which  the  blood 
flows,  a  little  consideration  will  convince  one  that  rigid  tubes 
are  wholly  unfit  for  the  purpose.  Somewhere  in  the  course  of 
the  circulation  the  blood  must  flow  sufficiently  slowly,  and 
through  vessels  thin  enough  to  permit  of  that  interchange  be- 
tween the  blood  and  the  tissues,  through  the  medium  of  the 
lymph,  which  is  essential  from  every  point  of  view.  The  main 
vessels  must  have  a  strength  sufficient  to  resist  the  force  with 
which  the  blood  is  driven  into  them. 

Now,  it  is  possible  to  conceive  of  this  being  accomplished 
with  an  intermittent  flow ;  but  manifestly  it  would  be  a  great 
advantage,  from  a  nutritive  aspect,  that  the  flow  and  therefore 
the  supply  of  tissue  pabulum  be  constant.  With  a  jDump  regu- 
larly intermittent  in  action,  provided  with  valves,  elastic  tubes 
having  a  resistance  in  them  somewhere  sufficient  to  keep  them 
constantly  over-distended,  and  a  collection  of  small  vessels  with 
walls  of  extreme  thinness,  in  which  the  blood-current  is  great- 
ly slackened,  a  steady  blood-flow  would  be  maintained,  as  the 
student  may  readily  convince  himself,  by  a  few  experiments  of 
a  very  simple  kind : 

1.  To  show  the  difference  between  rigid  tubes  and  elastic 
ones,  let  a  piece  of  glass  rod,  drawn  out  at  one  end  to  a  small 
diameter,  have  attached  to  the  other  end  a  Higginson's  (two- 
bulb)  syringe,  communicating  with  a  vessel  containing  water. 
Every  time  the  bulb  is  squeezed,  water  flows  from  the  end  of 
the  glass  rod,  but  the  outflow  is  perfectly  intermittent. 

2.  On  the  other  hand,  with  a  long  elastic  tube  of  India-rub- 
ber, ending  in  a  piece  of  glass  rod  drawn  out  to  a  point  as  be- 
fore, if  the  action  of  the  pump  (bulb)  be  rapid  the  outflow  will 
be  continuous.  An  apparatus  that  every  practitioner  of  medi- 
cine requires  to  use  answers  i)erhaps  still  better  to  illustrate 
these  and  other  principles  of  the  circulation,  such  as  the  pulse, 
the  influence  of  the  force  and  frequency  of  the  heart-beat  on  the 
bloofl-pressure,  etc.  We  refer  to  a  two-bulb  atomizer,  the  bulb 
nearer  the  outflow  serving  to  maintain  a  constant  air-pressure. 

We  may  now  examine  the  most  perfect  form  of  heart 
known,  that  of  the  mammal,  in  order  to  ascertain  how  far  it 
and  its  adjunct  tuljos  answer  to  a  priori  expectations. 

The  Mammalian  Heart. — In  order  that  the  student  may  gain 
a  correct  and  tliorough  knowledge  of  the  anatomy  of  the  heart 


218 


ANIMAL  PHYSIOLOGY. 


and  the  working  of  its  various  parts,  we  recommend  him  to 
pursue  some  such  course  as  the  following  : 

1.  To  consult  a  number  of  plates,  such  as  are  usually  fur- 
nished in  works  on  anatomy,  in  order  to  ascertain  in  a  general 
way  the  relations  of  the  heart  to  other  organs,  and  to  the  chest 
wall,  as  well  as  to  become  familiar  with  its  own  structure. 

2.  To  supplement  this  with  reading  the  anatomical  descrip- 
tions, without  too  great  attention  to  details  at  first,  but  with 
the  object  of  getting  his  ideas  clear  so  far  as  they  go. 

3.  Then,  with  plates  and  descriptions  before  him,  to  examine 
several  dead  specimens  of  the  heart  of  the  sheep,  ox,  pig,  or 
other  mammal,  first  somewhat  generally,  then  systematically, 
with  the  purpose  of  getting  a  more  exact  knowledge  of  the 

various  structures  and 
their  anatomical  as  well 
as  physiological  relations. 

We  would  not  have 
the  student  confine  his 
attention  to  any  single 
form  of  heart,  for  each 
shows  some  one  structure 
better  than  the  others ; 
and  the  additional  advan- 
tages of  comparison  are 
very  great.  The  heart  of 
the  ox,  from  its  size,  is 
excellent  for  the  study  of 
valvular  action,  and  the 
framework  with  which 
the  muscles,  valves,  and 
vessels  are  connected ; 
while  the  heart  of  the  pig 
(and  dog)  resemble  the 
human  organ  more  close- 
ly than  most  others  that 
can  be  obtained. 

It  will  be  found  very 
helpful  to  perform  some 
of  the  dissections  under 

Fia.  196.— The  left  auricle  and  ventricle  opened  and            .                 -\    i       J_^  j? 

part  of  their  walls  removed  to  show  their  cavities  Water,  and.    by  the  USe    01 

(Allen  Thomson).     1,  ri^ht  pulmonary  vein  cut  . ,   .                                    , ,  n     •  -i 

short :  1',  cavity  of  left  auricle ;  3,  thick  wall  of  thlS    Or   SOme    Other    fiuid 

left  ventricle;  4,  portion  of  the  same  with  papillary  ,-,               ,.              j?     /i  ^ 

muscle  attached  ;  5,  5',  the  other  papillary  mus-  tJie    aCtlOU    Ot    tlie  ValVCS 

cles  ;  6,  one  segment  of  the  mitral  valve  ;  7,  in                 t        ^                -i  • , 

aorta  is  placed  over  the  semilunar  valves.  may  06   leameCl    aS  it   Can 


THE  CIRCULATION  OF  THE  BLOOD. 


219 


in  no  other  way.  By  a  little  manipulation  the  heart  may  be  so 
held  that  water  may  be  poured  into  tlie  orifices,  prepared  by  a 
removal  of  a  jiortion  of  the  blood-vessels  or  the  auricles,  when 
the  valves  may  be  seen  closing  together,  and  thus  revealing 
their  action  in  a  way  which  no  verbal  or  pictorial  representa- 
tions can  do  at  all  adequately. 


Fio.  197.— View  of  the  orifices  Oi  the  heart  from  below,  the  whole  of  the  ventricles  having 
been  cut  away  (after  Huxley).  RAV,  right  auriculo-veiitric-ular  orifice,  surrounded  by 
the  three  flaps,  t.  v.  1,  t.  v.  2.  t.  v.  3,  of  the  tricuspid  valve,  which  are  stretched  by  weights 
attached  to  the  chorclrp  terulinere.  LA  T,  left  auriculo-veutricular  orifice,  etc.  PA,  orifice 
of  the  pulmonary  artery,  the  semilunar  valves  represented  as  having  met  and  closed 
together.    AO,  orifice  of  the  aorta. 

A  heart  thoroughly  boiled  and  allowed  to  get  cold  shows, 
on  being  pulled  somewhat  apart,  the  course,  attachment,  and 
other  features  of  the  fibers  very  well,  as  also  the  skeleton  of 
the  organ,  which  may  be  readily  separated. 

When  this  has  all  been  done,  the  half  is  not  yet  accom- 
])li8hed.  A  visit  to  an  abattoir  will  now  repay  amply  for  the 
time  spent.  Animals  are  there  killed  and  eviscerated  so  rapidly 
that  an  observer  may  not  only  gain  a  good  i)ractical  acquaint- 
ance with  the  relations  of  the  heart  to  other  parts,  but  may 
often  see  the  organ  still  living  and  exemplifying  that  action 
peculiar  to  it  as  it  gradually  approaches  quiescence  and  death 
— a  matter  of  the  utmost  importance. 

If  the  student  will  then  compare  what  he  has  learned  of  the 
mammalian  heart  in  this  way  with  the  behavior  of  the  heart 
of  a  frog,  snake,  fish,  turtle,  or  other  animal  that  may  be  killed 
after  brief  ether  narcosis,  without  cessation  of  the  heart's  ac- 


220 


ANIMAL  PHYSIOLOGY. 


tion,  he  will  have  a  broader  basis  for  his  cardiac  physiology 
than  is  usual ;  and  we  think  we  may  promise  the  medical  stu- 
dent, who  will  in  this 
FA  ^^^     -,_  g^j^(j  other  ways  that 

may  occur  to  him 
supplement  the  usual 
work  on  the  human 
cadaver,  a  pleasure 
and  profit  in  the 
study  of  heart  -  dis- 
ease which  come  in 
no  other  way. 

With  the  view  of 
assisting  the  obser- 
vation of  the  student 
as  regards  the  heart 
of  the  mammal,  we 
would  call  special  at- 
tention to  the  follow- 
ing points  among 
others :  Its  method  of 
suspension,  chiefly  by 
its  great  vessels ;  the 
strong  fibrous  frame- 
work for  the  attachment  of  valves,  vessels,  and  muscle-fibers ; 
the  great  complexity  of  the  arrangement  of  the  latter;  the 
various  lengths,  mode  of  attachment,  and  the  strength  of  the 
inelastic  chordse  tendineae  ;  the  papillary  muscles  which  doubt- 
less act  at  the  moment  the  valves  flap  back,  thus  preventing 
the  latter  being  carried  too  far  toward  the  auricles,  the  pocket- 
ing action  of  the  semilunar  valves,  with  their  strong  margin 
and  meeting  nodules  {corpora  aurantii) ;  the  relative  thickness 
of  auricles  and  ventricles,  and  the  much  greater  thickness  of 
the  walls  of  the  left  than  of  the  right  ventricle — differences 
which  are  related  to  the  work  these  parts  perform. 

The  latter  may  be  well  seen  by  making  transverse  sections 
of  the  heart  of  an  animal,  especially  one  that  has  been  bled  to 
death,  which  specimen  also  shows  how  the  contraction  of  the 
heart  obliterates  the  ventricular  cavity. 

It  will  also  be  well  worth  while  to  follow  up  the  course  of 
the  coronary  arteries,  noting  especially  their  point  of  origin. 

The  examination  of  the  valves  of  the  smaller  hearts  of  cold- 
blooded animals  is  a  matter  of  greater  difficulty  and  is  facili- 


ivz 


Fig.  198.— Orifices  of  the  heart  seen  from  above,  after  the 
auricles  and  great  vessels  had  been  cut  away  (after 
Huxley).  PA,  pulmonary  artery,  with  its  semilunar 
valves.  ^4o,  aorta  in  a  similar  condition.  iJ^F,  right 
auriculo  -  ventricular  orifice,  with  m.  v.  1  and  2  flaps 
of  mitral  valve  ;  h,  style  passed  into  coronary  vein. 
On  the  left  part  of  LA  V  the  section  of  the  auricle  is 
carried  through  the  auricular  appendage,  hence  the 
toothed  appearance  due  to  the  portions  in  relief  cut 
across. 


THE  CIRCULATION   OF   THE   BLOOD. 


221 


tated  by  dissection  under  water  with  the  help  of  a  lens  or  dis- 
secting niicroscoj)e ;  but  even  without  these  instruments  much 
may  be  learned,  and  certainly  that  the  valves  are  relatively  to 
those  of  the  mammalian  heart  imperfectly  developed,  will  be- 
come very  clear. 


Circulation  of  the  Blood  in  the  Mammal. 

It  is  highly  important  and  quite  possible  in  studying  the 
circulation  to  form  a  series  of  mental  pictures  of  what  is  trans- 
piring. It  will  be  borne  in  mind  that  there  is  a  set  of  elastic 
tubes  of  relatively  thick  walls,  standing  open  when  cut  across, 
dividing  into  smaller  and  smaller  branches,  and  finally  ending 
in  vessels  of  more  than  cobweb  fineness,  and  opening  out  into 
others,  that  become  larger  and  larger  and  fewer  and  fewer,  till 
they  are  gathered  up  into  two  of  great  size  which  form  the  right 
auricle.  The  larger  pipes  consist 
everywhere  of  elastic  tissue  prop- 
er, muscular  tissue  (itself  elas- 
tic), fibrous  tissue,  and  a  flat  epi- 
thelial lining,  so  smooth  that  the 
friction  therefrom  must  be  mini- 
mal as  the  blood  flows  over  it. 

The  return  tubes  or  veins  are 
like  the  arteries,  but  so  thin  that 
their  walls  fall  together  when  cut 
across.  They  are  different  from 
all  the  other  blood-tubes  in  that 
they  possess  valves  opening  to- 
ward the  heart  throughout  their 
course.  The  veins  are  at  least 
twice  as  numerous  as  the  arte- 
ries, and  their  capacity  many 
times  greater.  The  small  vessels 
or  capillaries  are  so  abundant 
and  wide-spread  that,  as  is  well 
known,  thcj  smallest  cut  any- 
where gives  rise  to  a  flow  of  blood, 
owing  to  section  of  some  of  these 
tubes,  which,  it  will  be  remem- 
bered, are  not  visible  to  the  un- 
aided eye.  It  is  estimated  that  their  united  area  is  several 
hundred  (500  to  800)  times  that  of  the  arteries. 


Fia.  199.— Various  layers  of  ihr  walls  of  a 
small  artery  (Laiidois).  c,  endothelium  ; 
/.  (',  internal  ehislie  lamina  ;  c.  rn,  circu- 
lar mus<Milar  fibers  of  the  middle  coat; 
c.  t.  connective  tissue  of  the  outer  coat, 
or  T.  adventitia. 


222 


ANIMAL  PHYSIOLOGY. 


If  we  suppose  tlie  epithelial  lining  pushed  out  of  a  small 
artery  we  have,  so  far  as  structure  alone  goes,  a  good  idea  of  a 
capillary — i.  e.^  its  walls  are  but  one  cell  thick,  and  these  cells 


Fig.  200. 


Fig.  201. 


Fig.  200. — Vein  with  valves  lying  open  (Dalton). 

Fig.  201.— Vein  with  valves  closed,  the  blood  passing  on  by  a  lateral  branch  below  (Dalton). 

though  long  are  extremely  thin,  so  that  it  is  qnite  easy  to  un- 
derstand how  it  is  that  the  amoeboid  corpuscles  can,  under  cer- 


FiG.  202.— Capillary  blood-vessels  (.Landois).    The  cement-substance  between  the  endothelium 
has  been  rendered  dark  by  silver  nitrate,  and  the  nuclei  made  prominent  by  staining. 


tain  circumstances,  push  their  way  through  its  probably  semi- 
fluid walls. 

From  what  has  been  said,  it  will  be  seen  that  the  whole  col- 
lection of  vascular  tubes  may  be  compared  to  two  inverted  fun- 


THE   CIRCULATION  OF  THE  BLOOD. 


223 


Fig.  203.— Diagram  to  illustrate  the  relative  proportions  of  the  aggregate  sectional  area  of  the 
different  parts  of  the  vascular  system  (after  Yeo).    A,  aorta  ;  C,  capillaries  ;  V,  veins. 

nels  or  cones  with  the  smaller  end  toward  the  heart  and  the 
widest  portions  representing  the  capillaries. 


The  Action  of  the  Mammalian  Heart. 

Very  briefly  what  takes  place  may  be  thus  stated :  The 
right  auricle  contracting  squeezes  the  blood  through  the  au- 
riculo-ventricular  opening  into  the  right  ventricle,  never  quite 
emptying  itself  probably ;  immediately  after  the  right  ventricle 
contracts,  by  which  its  valves  are  brought  into  sudden  tension 
and  apposition,  thus  preventing  reflux  into  the  auricle ;  while 
the  bloijd  within  it  takes  the  path  of  least  resistance,  and  the 
only  one  open  to  it  into  the  pulmonary  artery,  and  by  its 
branches  is  conveyed  to  the  capillaries  of  the  lungs,  from 
which  it  is  returned  freed  from  much  of  its  carbonic  anhy- 
dride and  replenished  with  oxygen,  to  the  left  auricle,  whence 
it  proceeds  in  a  similar  manner  into  the  great  arterial  main, 
the  aorta,  for  general  distribution  throughout  the  smaTlK' 
arteries  and  the  capillaries  to  the  most  remote  as  well  as  the 
nearest  parts,  from  which  it  is  gathered  up  by  the  veins  and 
retunuid  laden  with  many  impurities,  and  robbed  of  a  large 
proportion  of  its  useful  matters,  to  the  right  side  of  the  heart. 

It  will  be  remembered  that  corresponding  subdivisions  of 
each  side  of  the  heart  act  simultaneously,  and  that  any  decided 


224 


ANIMAL  PHYSIOLOGY. 


departure  from  this  harmony  of  rhythm  would  lead  to  serious 
disturbance. 


Superior  Vena  Cava. 


Inferior  Vena  Cava. 


Capillaries  of  Liver. 
Portal  Vein. 


Capillaries  of  the 
Head,  etc. 


Pulmonary  Capil- 
laries. 


Blain  Arterial  Trunk. 


Capillaries  of 
Splanchnic  Area. 


Capillaries  of  Trunk 
and  Lower  Ex- 
tremities. 


Fig.  804.— Diagram  of  the  circulation.  The  arrows  indicate  the  course  of  the  blood.  Though  the 
pulmonary  and  the  upper  and  the  lower  parts  of  the  systemic  circulation  are  represented 
so  as  to  show  the  distinctness  of  each,  it  will  be  also  apparent  that  they  are  not  independ- 
ent.   Relative  size  of  different  parts  of  the  system  is  only  very  generally  indicated. 


The  Velocity  of  the  Blood  and  Blood-Pressure. 

If  the  relative  capacity  and  arrangement  of  the  various 
parts  of  the  circulatory  system  be  as  has  been  represented,  it 
follows  that  we  may  predict  with  some  confidence,  apart  from 
experiment,  what  the  speed  of  the  flow  and  the  vascular  ten- 
sion must  be  in  different  parts  of  the  course  of  the  circulation. 

We  should  suppose  that,  in  the  nature  of  the  case,  the  ve- 
locity would  be  greatest  in  the  large  arteries,  gradually  dimin- 
ish to  the  capillaries,  in  which  it  would  be  much  the  slowest, 
and,  getting  by  degrees  faster,  would  reach  a  speed  in  the  largest 
veins  approaching  that  of  the  corresponding  arteries. 


THE   CIRCULATION   OP  THE  BLOOD.  225 

The  methods  of  determining  the  velocity  of  the  blood-stream 
have  not  entirely  surmounted  the  difficulties,  but  they  do  give 
results  in  harmony  with  the  above-noted  anticipations. 

The  area  of  the  great  aortic  trunk  being  so  much  less  than 
that  of  the  capillaries,  the  flow  in  that  vessel  we  should  expect  to 
be  very  much  swifter  than  in  the  arterioles  or  the  capillaries. 
Moreover,  there  must  be  a  great  difference  in  the  velocity  during 
cardiac  systole  and  diastole,  and  according  as  the  beat  of  the 
heart  is  forcible  or  otherwise.  But,  apart  from  these  more  ob- 
vious differences,  there  are  variations  depending  on  complex 
changes  in  the  peripheral  circulation,  owing  to  the  frequent 
variations  in  the  diameter  of  the  arterioles  in  different  parts, 
as  well  as  differences  in  the  resistance  offered  by  the  capillaries, 
the  causes  of  which  are  but  ill  understood,  though  less  obscure, 
we  think,  than  they  are  often  represented  to  be.  Since,  for  the 
maintenance  of  the  circulation,  the  quantity  of  blood  enter- 
ing and  leaving  the  heart  must  be  equal,  in  consequence  of  the 
sectional  area  of  the  great  veins  that  enter  the  heart  being 
greater  than  that  of  the  aorta,  it  follows  that  the  venous  flow 
even  at  its  quickest  is  necessarily  slower  than  the  arterial. 

Comparative. — There  must  be  great  variations  in  velocity  in 
different  animals,  as  such  measurements  as  have  been  made 
demonstrate.  Thus,  in  the  carotid  of  the  horse,  the  speed  of 
the  blood-current  is  calculated  as  about  306  mm.,  in  the  dog  at 
from  205  to  357  mm.  These  results  can  not  be  considered  as 
more  than  fair  approximations. 

Highly  important  is  it  to  note  that  the  rate  of  flow  in  the 
capillaries  of  all  animals  is  very  slow  indeed,  not  being  as  much 
as  1  mm.  in  a  second  in  the  larger  mammals.  The  time  occu- 
pied by  the  circulation  is  also,  of  course,  variable,  being  as  a 
rule  shorter  the  smaller  the  animal.  As  the  result  of  a  num- 
ber of  calculations,  though  by  methods  that  are  more  or  less 
faulty,  the  following  law  may  be  laid  down  as  meeting  ajjproxi- 
mately  the  facts  so  far  as  warm-blooded  animals  are  concerned : 

The  circulation  is  effected  by  27  heart-beats;  thus,  for  a 
man  with  a  i>ulse  of  81,  the  time  occupied  in  the  completion  of 
the  course  of  the  blood  from  and  to  the  heart  would  be  f4-  =  3  ; 
i.  e,,  the  circulation  is  completed  three  times  in  one  minute,  or 
its  period  is  twenty  seconds;  and  it  is  to  be  well  borne  in  mind 
that  by  far  the  greater  part  of  this  time  is  occupied  in  travers- 
ing the  capillaries. 


226 


ANIMAL  PHYSIOLOGY. 


The  Circulation  under  the  Microscope. 

There  are  few  pictures  more  instructive  and  impressive  than 
a  view  of  the  circulation  of  the  blood  under  the  microscope. 
It  is  well  to  have  similar  preparations^  one  under  a  low  power 
and  another  under  a  magnification  of  300i:o  500  diameters.  With 
the  former  a  ^ew  of  arterioles,  veins,  and  capillaries  may  be 


Fig.  205.—  Portion  of  the  web  of  a  frog's  foot  as  seen  under  a  low  magnifying  power,  showing 
the  blood-vessels,  and  in  one  corner  the  pigment-spots  (after  Huxley),  a,  small  arteries 
(arterioles) ;  v,  spiall  veins.  The  smaller  vessels  are  the  capillaries.  The  course  of  the 
blood  is  indicated  by  arrows. 

obtained  at  once.  Many  different  parts  of  animals  may  be  used, 
as  the  web  of  the  frog's  foot,  its  tongue,  lung,  or  mesentery ; 
the  gill  or  tail  of  a  small  fish,  tadpole,  etc. 

The  relative  size  of  the  vessels ;  the  speed  of  the  blood-flow ; 
the  greater  velocity  of  the  central  part  of  the  stream ;  the  aggre- 
gation of  colorless  corpuscles  at  the  sides  of  the  vessels,  and  the 
occasional  passage  of  one  through  a  capillary  wall,  when  the 
exposure  has  lasted  some  time ;  the  crowding  of  the  red  cells ; 
their  plasticity ;  the  small  size  of  some  of  the  capillaries,  barely 


THE  CIRCULATION  OF  THE  BLOOD. 


227 


allowing  the  corpuscles  to  be  squeezed  through ;  the  changes  in 
the  velocit)^  of  the  current,  especially  in  the  capillaries ;  its  pos- 
sible arrest  or  retrocession ;  the  velocity  in  one  so  much  greater 
than  in  its  neighbor,  without  very  obvious  cause — all  this  and 
much  more  forms,  as  we  have  said,  a  remarkable  lesson  for  the 
thinking  student.  This,  like  all  microscopic  views,  especially 
if  motion  is  represented,  has  its  fallacies.    It  is  to  be  remem- 


Fio.  206. — Circulation  in  the  web  of  the  frog's  foot  (Wagner).  F,  venous  trunk  composed  of 
the  three  principal  branches  (v,  v,  v),  covered  with  a  plexus  of  smaller  vessels.  The  whole 
is  dotted  over  with  pigment  masses. 

bered  that  the  movements  are  all  magnified,  or  else  one  is  apt 
to  suppose  the  capillary  circulation  extremely  rapid,  whereas 
it  is  like  that  of  the  most  sluggish  part  of  a  stream,  and  very 
irregular. 


The  Characters  op  the  Blood-Flow. 

If  an  artery  be  opened,  the  blood  is  seen  to  flow  from  it  in 
a  constant  stream,  with  periodic  exaggerations,  which,  it  is 
found,  answer  to  the  heart-beats ;  in  the  case  of  veins  and 
capillaries  the  flow  is  also  constant,  but  shows  none  of  the 
spurting  of  the  arterial  stream,  nor  has  the  cardiac  beat  appar- 
ently an  equal  modifying  effect  upon  it. 

We  have  already  explained  why  the  flow  should  be  constant, 
though  it  would  1)0  well  to  be  clearer  as  to  the  peripheral  re- 
sistance.    The  anKJunt  of  friction  from  linings  so  smooth  as 


228  ANIMAL  PHYSIOLOGY. 

those  of  the  blood-vessels  can  not  be  considerable.  Whence, 
then,  arises  that  friction  which  keeps  the  arterial  vessels  always 
distended  by  its  backward  influence  ?  The  microscopic  study 
of  the  circulation  helps  to  answer  this  question.  The  plas- 
ticity of  the  corpuscles  and  of  the  vessel  walls  themselves 
must  be  taken  into  account,  in  consequence  of  which  a  drag- 
ging influence  is  exerted  whenever  the  corpuscles  touch  the 
wall,  which  must  constantly  happen  with  vast  numbers  of 
them  in  the  smallest  vessels  and  especially  in  the  capillaries. 
The  arrangement  of  capillaries  into  a  mesh-work,  must  also,  in 
consequence  of  so  many  angles,  be  a  source  of  much  friction. 

The  action  of  the  corpuscles  on  one  another  may  be  com- 
pared to  a  crowd  of  people  hurrying  along  a  narrow  passage — 
the  obstruction  comes  from  interaction  of  a  variety  of  forces, 
owing  to  the  crowd  itself  rather  than  the  nature  of  the  thor- 
oughfare. We  must  set  down  a  great  deal  to  the  influence  of 
the  corpuscles  on  one  another,  as  they  are  carried  along,  accord- 
ing to  mechanical  principles ;  but,  as  we  shall  see  later,  other 
and  more  subtile  factors  play  a  part  in  the  capillary  circulation. 
Owing  to  the  peripheral  resistance  and  the  pumping  force  of 
the  heart,  the  arteries  become  distended,  so  that,  during  cardiac 
diastole,  their  recoil,  owing  to  the  closure  of  the  semilunar 
valves,  forces  on  the  blood  in  a  steady  stream.  It  follows,  then, 
that  the  main  force  of  the  heart  is  spent  in  distending  the 
arteries,  and  that  the  immediate  propelling  force  of  the  circu- 
lation is  the  elasticity  of  the  arteries  in  which  the  heart  stores 
up  the  energy  of  its  systole  for  the  moment, 

Blood-Pressure. 

Keeping  in  mind  our  schematic  representation  of  the  circu- 
lation, we  should  expect  that  the  blood  must  exercise  a  certain 
pressure  everywhere  throughout  the  vascular  system ;  that  this 
blood-pressure  would  be  highest  in  the  heart  itself ;  considera- 
ble in  the  whole  arterial  system,  though  gradually  diminishing 
toward  the  capillaries,  in  which  it  would  be  feeble ;  lower  still 
in  the  smaller  veins  ;  and  at  its  minimum  where  the  great  veins 
enter  the  heart.  Actual  experiments  confirm  the  truth  of  these 
views ;  and,  as  the  subject  is  one  of  considerable  importance, 
we  shall  direct  attention  to  the  methods  of  estimating  and  re- 
cording an  animal's  blood-pressure. 

First  of  all,  the  well-known  fact  that,  when  an  artery  is  cut, 
the  issuing  stream  spurts  a  certain  distance,  as  when  a  water- 


THE  CIRCULATIOX   OF   THE   BLOOD.  229 

main,  fed  from  an  elevated  reservoir,  bursts,  or  a  hydrant  is 
opened,  is  itself  a  proof  of  the  existence  of  blood-pressure,  and 
is  a  crude  measure  of  tlie  amount  of  the  pressure. 

One  of  the  simplest  and  most  impressive  ways  of  demon- 
strating blood-pressure  is  to  connect  the  carotid,  femoral,  or 
other  large  artery  of  an  animal  by  means  of  a  small  glass  tube 
(drawn  out  in  a  peculiar  manner  to  favor  insertion  and  reten- 
tion by  ligature  in  the  vessel),  known  as  a  cannula,  by  rubber 
tubing,  with  a  long  glass  rod  of  bore  approaching  that  of  the 
artery  opened,  into  which  the  blood  is  allowed  to  flow  through 
the  above-mentioned  connections,  while  it  is  maintained  in  a 
vertical  position. 

To  prevent  the  rapid  coagulation  of  the  blood  in  such  ex- 
periments, it  is  customary  to  fill  the  cannula  and  other  tubes 
to  a  certain  extent,  at  least,  with  a  solution  of  some  salt  that 
tends  to  retard  coagulation,  such  as  sodium  carbonate  or  bicar- 
bonate, magnesium  sulphate,  etc.  If  other  connections  are 
made  in  a  similar  way  with  smaller  arteries  and  veins,  it  may 
be  seen  that  the  height  of  the  respective  columns,  representing 
the  blood-pressure,  varies  in  each  and  in  accordance  with  ex- 
pectations. 

While  all  the  essential  facts  of  blood-pressure  and  many 
others  may  be  illustrated  by  the  above  simple  methods,  it  is 
inadequate  when  exact  measurements  are  to  be  made  or  the 
results  to  be  recorded  for  permanent  preservation ;  hence  appa- 
ratus of  a  somewhat  elaborate  kind  has  been  devised  to  accom- 
plish these  purposes. 

The  graphic  methods  are  substantially  those  already  ex- 
plained in  connection  with  the  physiology  of  muscle;  but, 
since  it  is  often  desirable  to  maintain  blood-pressure  experi- 
ments for  a  considerable  time,  instead  of  a  single  cylinder,  a 
series  so  connected  as  to  provide  a  practically  endless  roll  of 
paper  (Fig,  208)  is  employed. 

When,  in  tlie  sort  of  experiments  referred  to  above,  the 
height  of  the  fluid  used  in  the  glass  tube  to  prevent  coagula- 
tion just  suffices  to  prevent  outflow  from  the  artery  into  the 
connections,  we  have,  of  course,  in  this  a  measure  of  the  blood- 
pressure  ;  however,  it  is  convenient  in  most  instances  to  use 
mercury,  contained  in  a  glass  tube  bent  in  the  form  of  a  U,  for 
a  measure,  as  shown  in  the  subjoined  illustration.  It  is  also 
desirable,  in  order  to  prevent  outflow  of  the  blood  into  the 
apparatus,  to  get  up  a  pressure  in  the  U-tube  or  manomc^ter  as 
near  as  may  be  equal  U)  that  of  the  animal  to  be  employed  in 


230 


ANIMAL  PHYSIOLOGY. 


Fig.  207.— Apparatus  used  in  making  a  blood-pressure  experiment  (after  Foster),  pb^  pressure- 
bottle,  elevated  so  as  to  raise  the  pressure  several  inches  of  mercury,  as  seen  in  the  ma- 
nometer (m)  below.  It  contains  a  saturated  solution  of  sodium  carbonate  ;  r.t.  rubber  tune 
connecting  the  pb  with  the  leaden  tube  ;  U,  tube  made  of  lead,  so  as  to  be  pliable,  Jft  have 
rigid  walls  ;  s.c.a,  stop-cock,  the  top  of  which  is  removable,  to  allow  escape  of  bubbles  ot 
a§  :  »,  the  pen,  writing  on  the  roll  of  paper,  r.  The  former  floats  on  the  mercury  ;  .w.  the 
manoiiieter,  the  shaded  portion  of  the  bent  tube  denoting  the  mercury,  the  rest  is  fUled 
with  a  fluid  unfavorable  to  the  coagulation  of  the  blood,  and  derived  from  the  pressure- 


THE  CmCULATIOX  OF  THE  BLOOD. 


231 


bottle  ;  ca,  the  carotid,  in  which  is  placed  the  canula,  and  below  the  latter  a  forceps,  which 
may  be  removed  when  the  blood-pressure  is  to  be  actuallj'  measured.  The  registration  of 
the  height,  variation,  etc.,  of  blood-pressure,  is  best  made  on  a  continuous  roll  of  paper,  as 
seen  in  Fig  208. 

the  experiment.  This  may  be  effected  in  a  variety  of  ways, 
one  of  the  most  convenient  of  which  is  by  means  of  a  vessel 
containing  some  saturated  sodium  carbonate  or  similar  solu- 
tion in  connection  with  the  manometer. 

It  is  important  that  the  pressure  should  express  itself  as 
directly  and  truthfully  on  the  mercury  of  the  manometer  as 
possible,  hence  the  employment  of  a  tube  with  rigid  walls,  yet 
capable  of  being  bent  readily  in  different  directions  for  the  sake 
of  convenience. 

Mercury,  on  account  of  its  inertia,  is  not  free  from  objec- 
tion ;  and  when  very  delicate  variations  in  the  blood-pressure — 
e.  g.,  feeble  pulse-beats — are  to  be  indicated,  it  fails  to  express 
them,  in  which  case  other  fluids  may  be  employed. 


Fio.  208.— Large  kj-mograph,  with  continuous  roll  of  paper  (Foster).  The  clock-work  ma- 
chinery unroU.s  the  paper  from  the  roll  C,  carries  it  smoothly  over  the  cylinder  B,  and  then 
wind.s'it  up  int<^)  the  roll  A.  Two  electro-magnetic  markers  are  seen  in  position  recording 
Intervals  of  time  on  the  moving  roll  of  paper.  A  manometer  may  be  fixed  in  any  con- 
venient position. 

It  will  be  noted  that  when  an  ordinary  cannula  is  used,  in- 
serted as  it  is  lengthwise  into  the  blood-vessel,  the  i)ressure 
recorded  is  not  that  on  the  side  of  the  vessel  into  which  it  is 
inserted  as  when  an-  piece  is  used,  but  of  the  vessel,  of  which 
the  one  in  question  is  a  branch.  The  blood-pressure,  in  the 
main  arterial  trunk  for  example,  must  depend  largely  on  the 
force  of  the  heart-beat ;  consequently  it  would  be  expected,  and  it 


232  ANIMAL  PHYSIOLOGY. 

is  actually  found,  that  the  pressure  varies  for  different  animals, 
size  having,  of  course,  in  most  instances  a  relation  to  the  result. 
It  has  been  estimated  that  in  the  carotid  of  the  horse  the  arte- 
rial pressure  is  150  to  200  mm.  of  mercury,  of  the  dog  100  to  175, 
of  the  rabbit  50  to  90.  Man's  blood-pressure  is  not  known,  but 
is  probably  high,  we  may  suppose  not  less  than  150  to  200  mm. 
After  the  fact  that  there  is  a  certain  considerable  blood- 
pressure,  the  other  most  important  one  to  notice  is  that  this 
blood-pressure  is  constantly  varying  during  the  experiment, 
and,  as  we  shall  give  reason  to  believe,  in  the  normal  animal ; 
and  to  these  variations  and  their  causes  we  shall  presently  turn 
our  attention. 

THE  HEART. 

The  heart,  being  one  of  the  great  centers  of  life,  to  speak 
figuratively,  it  demands  an  unusually  close  study. 

The  Cardiac  Movements. 

There  is  no  special  difficulty  in  ascertaining  the  outlines  of 
the  heart  by  means  of  percussion  on  either  the  dead  or  the 
living  subject.  Quite  otherwise  is  it  with  the  changes  in  form 
which  accompany  cardiac  action.  Attempts  have  been  made  to 
ascertain  the  alterations  in  position  of  the  heart  with  respect 
to  other  parts,  and  especially  its  own  alterations  in  shape  dur- 
ing a  systole,  the  chest  being  unopened,  by  the  use  of  needles 
thrust  into  its  substance  through  the  thoracic  walls  ;  but  the 
results  have  proved  fallacious.  Again,  casts  have  been  made 
of  the  heart  after  death,  in  a  condition  of  moderate  extension, 
prior  to  rigor  mortis  ;  and  also  when  contracted  by  a  hardening 
fluid.  These  methods,  like  all  others  as  yet  employed,  are  open 
to  serious  objections. 

Following  the  rapidly  beating  heart  of  the  mammal  with 
the  eye  produces  uncertainty  and  confusion  of  mind.  We  look 
to  instantaneous  photography  to  furnish  a  possible  way  out  of 
the  difficulty. 

It  may  be  very  confidently  said  that  the  mode  of  contrac- 
tion of  the  hearts  of  different  groups  of  vertebrates  is  variable, 
though  it  seems  highly  probable  that  the  divergences  for  mam- 
mals are  slight.  The  most  that  can  be  certainly  affirmed  of 
the  mammalian  heart  is,  that  during  contraction  of  the  ventri- 
cles they  become  more  conical ;  that  the  long  diameter  is  not 
appreciably   altered ;  that    the   antero  -  posterior   diameter  is 


THE   CIRCULATION   OP   THE   BLOOD.  233 

lengthened ;  and  that  the  left  ventricle  at  least  turns  on  its  own 
axis  from  left  to  right.  This  latter  may  be  distinctly  made  out 
by  the  eye  in  watching  the  heart  in  the  opened  chest. 

The  Impulse  of  the  Heart. 

When  one  places  his  hand  over  the  region  of  the  heart  in 
man  and  other  mammals,  he  experiences  a  sense  of  pressure 
varying  with  the  part  touched,  and  from  moment  to  moment. 
Instruments  constructed  to  convey  this  movement  to  recording 
levers  also  teach  that  certain  movements  of  the  chest  wall  cor- 
respond with  the  propagation  of  the  pulse,  and  therefore  to  the 
systole  of  the  heart.  It  can  be  recognized,  whether  the  hand 
or  an  instrument  be  used,  that  all  parts  of  the  chest  wall  over 
the  heart  are  not  equally  raised  at  the  one  instant.  If  the  beat- 
ing heart  be  held  in  the  hand,  it  will  be  noticed  that  during 
systole  there  is  a  sudden  hardening.  The  relation  of  the  apex 
to  the  chest  wall  is  variable  for  different  mammals,  and  with 
different  positions  of  the  body  in  man. 

As  a  result  of  the  investigation  which  this  subject  has  re- 
ceived, it  may  be  inferred  that  the  sudden  tension  of  the  heart, 
owing  to  the  ventricle  contracting  over  its  fluid  contents,  causes 
in  those  cases  in  which  during  diastole  the  ventricle  lies  against 
the  chest  wall,  a  sense  of  pressure  beneath  the  hand,  which  is 
usually  accompanied  by  a  visible  movement  upward  in  some 
part  of  the  thoracic  wall,  and  downward  in  adjacent  parts. 
The  exact  characters  of  the  cardiac  impulse  are  very  variable 
with  different  human  subjects.  The  term  "  apex-beat "  is  fre- 
quently employed  instead  of  cardiac  impulse,  on  the  assump- 
tion that  the  apex  of  the  heart  is  brought  into  sudden  contact 
with  the  thoracic  walls  from  which  it  is  supposed  to  recede 
during  diastole.  But,  in  some  positions  of  the  body  at  all 
ev^ents  in  a  certain  proportion  of  cases,  the  apex  of  the  heart 
lies  against  the  chest  wall  during  diastole,  so  that  in  these 
instances  certainly  such  a  view  would  not  be  wholly  correct. 
But  we  would  not  deny  that  in  some  subjects  there  may  be  a 
genuine  knock  of  the  apex  against  the  walls  of  the  chest  during 
the  ventricular  systole. 

It  will  not  be  forgotten  that  the  heart  lies  in  a  pericardial 
sac,  moistened  with  a  small  quantity  of  allmminous  fluid ;  and 
that  by  this  sac  the  organ  is  tethered  to  the  walls  of  tin;  chest 
by  its  mediastinal  fastenings;  so  that  in  receding  from  the 
chest  wall  the  latter  may  be  drawn  after  it ;  though  this  might 


234 


ANIMAL  PHYSIOLOGY. 


also  follow  from  the  intercostal  muscles  being  simply  unsup- 
ported when  the  heart  recedes. 

Investigation  of  the  Heart-Beat  from  within. 

By  the  use  of  apparatus  introduced  within  the  heart  of  the 
mammal  and  reporting  those  changes  susceptible  of  graphic 
record,  certain  tracings  have  been  obtained  about  the  details  of 


Fig.  209.— Marey's  cardiac  sound  which  may  be  used  to  explore  the  chambers  of  the  heart 
(after  Foster),  a,  is  made  of  rubber  stretched  over  a  wire  framework,  with  metallic 
supports  above  and  below  ;  6,  is  a  long  tube. 

which  there  are  uncertainty  and  disagreement,  though  they 
seem  to  establish  the  nature  of  the  main  features  of  the  cardiac 
beat  clearly  enough.     An  interpretation  of  such  traciijgs  in  the 


Right  auricle. 


Right  ventricle. 


Cardiac  impulse. 


Fig.  210.— Simultaneous  tracings  from  the  interior  of  the  right  auricle,  from  the  interior  of  the 
right  ventricle,  and  of  the  cardiac  impulse,  in  the  horse  (after  Chauveau  and  Marey). 
Tracings  to  be  read  from  left  to  right,  and  the  references  above  are  in  the  order  from  top 
to  bottom.  A  complete  cardiac  cycle  is  included  between  the  thick  vertical  lines  I  and  II. 
The  thin  vertical  lines  indicate  tenths  of  a  second.  The  gradual  rise  of  pressure  within  the 
ventricle  (middle  tracing)  during  diastole,  the  sudden  rise  with  the  systole,  its  maintenance 
with  oscillations  for  an  appreciable  time,  its  sudden  fall,  etc.,  are  all  well  shown.  There  is 
disagreement  as  to  the  exact  meaning  of  the  minor  curves  in  the  larger  ones. 


light  of  our  general  and  special  knowledge  warrants  the  fol- 
lowing statement. 


THE  CIRCULATION  OF  THE  BLOOD.  235 

1.  Both  auricular  and  ventricular  systole  are  sudden,  but 
the  latter  is  of  very  much  greater  diiration. 

2.  While  the  chest  wall  feels  the  ventricular  systole,  the  au- 
riculo-ventricular  valves  shield  the  auricle  from  its  shock. 

3.  During  diastole  in  both  chambers  the  pressure  rises 
gradually  from  the  inflow  of  blood ;  and  the  auricular  contrac- 
tion produces  a  brief,  decided,  though  but  slight  rise  of  press- 
ure in  the  ventricles. 

4.  The  onset  of  the  ventricular  systole  is  rapid,  its  maximum 
pressure  suddenly  reached,  and  its  duration  considerable. 

The  relations  of  these  various  events,  their  duration,  and  the 
corresponding  movements  of  the  chest  wall,  may  be  learned  by 
a  study  of  the  above  tracing  which  the  student  will  find  worthy 
of  his  close  attention. 

The  Cardiac  Sounds. 

Two  sounds,  differing  in  pitch,  duration,  and  intensity,  may 
be  heard  over  the  heart,  when  the  chest  is  opened  and  the 
heart  listened  to  by  means  of  a  stethoscope.  These  sounds  may 
also  be  heard,  and  present  the  same  characters  when  the  heart 
is  auscultated  through  the  chest  wall ;  hence  the  cardiac  im- 
pulse can  take  no  essential  part  in  their  production. 

The  sounds  are  thought  to  be  fairly  well  represented,  so  far 
as  the  human  heart  is  concerned,  by  the  syllables  lub,  chqj; 
the  first  sound  being  longer,  louder,  lower-pitched,  and  "  boom- 
ing "  in  quality ;  the  second  short,  sharp,  and  high-pitched. 

In  the  exposed  heart,  the  first  sound  is  heard  most  distinct- 
ly over  the  base  of  the  organ  or  a  little  below  it ;  while  the  sec- 
ond is  communicated  most  distinctly  over  the  roots  of  the  great 
vessels — that  is  to  say,  both  sounds  are  heard  best  oyer  the 
auriculo- ventricular  and  semilunar  valves  respectively.  When 
the  chest  wall  intervenes  between  the  heart  and  the  ear,  it  is 
found  that  the  second  sound  is  usually  heard  most  distinctly 
over  the  second  costal  cartilage  on  the  right ;  and  the  first  in 
the  fifth  costal  interspace  where  the  heart's  impulse  is  also 
often  most  distinct.  In  these  situations  the  arch  of  the  aorta 
in  the  one  case,  and  the  ventricular  walls  in  the  other,  are  close 
to  the  situations  referred  to  during  the  cardiac  systole;  hence 
it  is  inferred  that,  though  the  sounds  do  not  originate  directly 
beneath  these  spots,  they  are  best  propagated  to  the  chest  wall 
at  these  points. 

There  are,  however,  individual  differences,  owing  to  a  va- 


236  ANIMAL   PHYSIOLOGY. 

riety  of  causes,  which  it  is  not  always  possible  to  explain  fully 
in  each  case,  but  owing  doubtless  in  great  part  to  variations  in 
the  anatomical  relations. 

The  Causes  of  the  Sounds  of  the  Heart. — There  is  general  agree- 
ment in  the  view  that  the  second  sound  is  owing  to  the  closure 
of  the  semilunar  valves  of  the  aortic  and  pulmonary  vessels ; 
the  former,  owing  to  their  greater  tension  inconsequence  of  the 
higher  blood-pressure  in  the  aorta,  taking  much  the  larger  share 
in  the  production  of  the  sound,  as  may  be  ascertained  by  listen- 
ing over  these  vessels  in  the  exposed  heart.  When  these  valves 
are  hooked  back,  the  second  sound  disappears,  so  that  there  can 
be  no  doubt  that  they  bear  some  important  relation  to  the  cau- 
sation of  the  sound. 

In  regard  to  the  first  sound  of  the  heart  the  greatest  diver- 
sity of  opinion  has  prevailed  and  still  continues  to  exist.  The 
following  among  other  views  have  been  advocated  by  physi- 
ologists : 

1.  The  first  sound  is  caused  by  the  tension  and  vibration  of 
the  auriculo-ventricular  valves. 

2.  The  first  sound  is  owing  to  the  contractions  of  the  large 
mass  of  muscle  composing  the  ventricles. 

3.  The  sound  is  directly  traceable  to  eddies  in  the  blood. 

In  favor  of  the  first  view  it  was  argued  that  by  agreement 
the  second  sound  was  valvular,  and  why  not  the  first  ? — And 
again  that  malformations  of  the  valves  gave  rise  to  "  murmurs  " 
("  bruits"),  which  either  obscured  or  replaced  the  true  sound. 

The  second  opinion  was  supported  by  the  fact  that  the  larger 
the  heart  the  more  powerful  the  sound ;  that  when  the  blood 
was  cut  off  from  the  heart  by  ligature  of  the  vessels  success- 
ively, the  sound  could  still  be  heard ;  that  with  fatty  degenera- 
tion of  the  muscle-fibers  of  the  heart,  it  had  been  found  that 
the  sound  was  weak — and  similar  arguments. 

Recently  it  has  been  contended  very  strongly  that  the  first 
sound  may  be  heard  by  a  double  stethoscope  placed  over  an  ex- 
cised, bloodless,  mammalian  heart,  or  even  ventricle,  while  it 
still  beats. 

The  third  opinion  was  less  vigorously  upheld,  but  certain 
experiments  and  physical  phenomena  were  pointed  to  in  sup- 
port of  it. 

Against  the  arguments  adduced  above  it  may  be  stated  that 
the  first  sound  may  be  conceived  as  overpowered  by  a  bruit 
without  being  replaced  by  it  in  the  proper  sense  of  the  word. 
It  is  well  known  that  the  cardiac  muscle  is  peculiar,  occupying 


THE   CIRCULATIOX   OF   THE   BLOOD. 


237 


in  structure  a  position  intermediate  between  the  striped  vol- 
untary fibers  and  tlie  smooth  muscle-cells.  Numerous  investi- 
gations have  shown  that  the  heart  is  not  susceptible  of  true 


Fig.  2n. 


Fig.  212. 


Fig.  211.— Microscopic  appearances  of  fibers  from   the  heart.      The  cross-striae,  divisions 

(branching),  and  junctures  are  visible  (Landois). 
Fig.  212.— Muscular  fiber-cells  from  the  heart.    (.1  x  425.)    a,  line  of  juncture  between  two 

cells  ;  6,  c,  branching  cells. 


tetanic  contraction,  certainly  not  the  heart  of  the  mammal ;  so 
that  it  is  customary  to  term  the  cardiac  contraction  peristaltic. 
If  this  view  be  correct,  how  could  there  be  a  sound  produced  by 
muscular  contraction  alone  ?  To  this  it  has  been  replied  that 
the  sudden  tension  of  the  ventricular  wall  when  tightened  over 
the  blood  may  give  rise  to  vibrations  that  account  for  the 
sound ;  and  recent  investigations  have  shown  that  the  vibrations 
that  give  rise  to  the  sound  emitted  by  a  contracting  skeletal 
muscle  may  be  fewer  than  was  once  supposed.  The  statement 
that  a  sound  may  be  heard  from  the  excised  ventricle  under  the 
circumstances  above  mentioned  has  not  been  denied ;  but  its 
source  has  been  traced  to  the  action  of  the  heart  wall  against  the 
stethoscope — i.  e.,  some  believe  the  sound  to  be,  in  this  case, 
of  extrinsic  origin.  Most  physicians  would  be  very  loath  to 
abandon  the  view  that  the  valves  are  always  to  be  taken  into 
serious  account  as  a  factor  in  the  causation  of  the  sound. 

But,  looking  at  the  whole  question  broadly,  is  it  not  unrea- 
sonable to  exphiin  the  sound  resulting  from  such  a  complex  act 
as  the  contraction  of  the  heart  and  what  it  implies  in  the  light 
of  any  single  factor  ?  That  such  narrow  and  exclusive  views 
should  liave  been  })ro[)agatod,  even  by  eminent  j)hysi()logists, 
should  admonisli  tlie  student  to  receive  witli  great  caution  ex- 


238  ANIMAL  PHYSIOLOGY. 

planations  of  the  working  of  complex  organs,  based  on  a  single 
experiment,  observation,  or  argument  of  any  kind. 

The  view  we  recommend  the  student  to  adopt  in  the  light  of 
our  present  knowledge  is,  that  the  first  sound  is  the  result  of 
several  causative  factors,  prominent  among  which  are  the  sud- 
den tension  of  the  auriculo-ventricular  valves,  and  the  contrac- 
tion of  the  cardiac  muscle,  not  leaving  out  of  the  account  the 
possible  and  probable  influence  of  the  blood  itself  through 
eddies  or  otherwise ;  nor  would  we  ridicule  the  idea  that  in 
some  cases,  at  all  events,  the  sound  may  be  modified  in  quality 
and  intensity  by  the  shock  given  to  the  chest  wall  during  sys- 
tole. 

Endo-Cardiac  Pressures. 

Bearing  in  mind  the  relative  extent  of  the  pulmonary  and 
systemic  portions  of  the  circulation,  we  should  suppose  that 
the  resistance  to  be  overcome  in  opening  the  aortic  valves  and 
lifting  the  column  of  blood  that  keeps  them  pressed  together, 
would  be  much  greater  in  the  left  ventricle  than  in  the  right ; 
or,  in  other  words,  that  the  intra-ventricular  pressure  of  the 
left  side  of  the  heart  would  greatly  exceed  that  of  the  right, 
and  this  is  confirmed  by  actual  experiment. 

By  means  of  an  instrument  known  as  the  maximum  and 
minimum  manometer,  the  highest  and  lowest  pressure  within 
any  chamber  of  the  heart  may  be  learned  approximately.  As 
a  specimen  measurement  it  may  be  stated  that  it  has  been 
found  that  in  a  dog  the  greatest  pressure  was  140  mm.  of  mer- 
cury for  the  left  ventricle,  for  the  right  only  60,  and  for  the 
right  auricle  20.  But  it  is  also  found — a  matter  not  quite  so 
obvious — that  a  minimum  pressure  proportionate  to  the  maxi- 
mum may  exist  in  all  the  chambers  of  the  heart ;  and  the  press- 
ure may  fall  below  that  of  the  atmosphere,  or  be  negative.  By 
the  same  method  it  was  found  that  in  a  dog  the  negative  pressure 
varied  between  —52  and  —20  mm.  of  mercury  for  the  left  ven- 
tricle and  —17  to  —16  mm.  for  the  right,  with  —12  to  —7  mm.  for 
the  right  auricle.  As  will  be  shown  later,  part  of  this  diminished 
pressure  is  due  to  the  effect  of  the  respiratory  movements ;  and, 
indeed,  more  recent  experiments  seem  to  show  that  ordinarily, 
with  the  heart  beating  with  its  usual  rate  and  force,  the  nega- 
tive pressure  or  suck  from  its  own  action  is  comparatively 
slight.  The  discussion  of  the  cause  of  this  negative  pressure, 
like  the  related  subject  of  the  cause  of  the  heart's  diastole,  has 
given  rise  to  much  difference  of  opinion. 


THE  CIRCULATION   OP   THE  BLOOD. 


239 


Some  find  it  difficult  to  understand  how  the  heart  after  sys- 
tole may  regain  its  original  form  apart  from  the  assistance  of 
diastolic  muscles,  which  are  assumed  to  act  so  as  to  antagonize 
those  causing  systole. 

Others  think  the  elasticity  of  the  heart's  muscle  sufficient  of 
itself  to  account  for  the  organ's  return  to  its  original  form. 

But  there  is  surely  a  misconception  involved  in  both  of 
these  views. 

If  small  portions  of  the  heart  of  the  frog,  tortoise,  or  other 
cold-blooded  animal,  just  removed  from  the  body,  be  observed 
under  a  microscope  it  will  be  seen  that  they  alternately  con- 
tract and  relax.  Now,  it  is  only  necessary  to  sujjpose  that  the 
relaxation  of  the  heart  is  complete  after  each  systole,  to  under- 
stand how  even  an  empty  heart  regains  its  diastolic  form. 

That  there  should  be  a  negative  pressure  in,  say,  the  left 
ventricle,  follows  naturally  enough  from  the  fact  that  not  only 
are  the  contents  of  the  ventricle  expelled  with  great  sudden- 
ness, but  that  its  walls  remain  (see  Figs.  210  and  214)  pressed 
together  for  a  considerable  portion  of  the  time  occupied  by  the 
whole  systole ;  so  that  in  relaxation  it  follows  that  there  must 


FlO.  213.— Diajrram  showing  Die  relative  lieitclif,  of  the  hlood-pressure  in  (lifTereiif  ])art8  of  the 
vfttwjiilar  svHtem  (after  Yeo).  /(,  heart  ;  ii,  art-erioles  ;  v,  Ktnall  veins  ;  ,(,  arterieH  ;  c,  cap- 
illarieH  ;  I  ,  liirge  veins  :  //.  V,  representing  Uio  zero-line,  i.  e.,  atrnoHjilieric  pressure  ;  the 
>)lo<Kl-preKSure  is  indicattnl  by  the  heijrht  of  the  curve.  The  numbers  on  the  left  K've  the 
preHsure,  approximaUily,  in  mm.  of  mercury. 

be  an  empty  cavity  to  fill,  or  that  there  must  be  an  aspiratory 
efiFect  toward  the  ventricle ;  hence  also  one  factor  in  the  closure 
of  the  semilunar  valves. 


240 


ANIMAL  PHYSIOLOGY. 


It  tliTis  appears  that  the  heart  is  not  only  a  force-pump  but 
also  to  some  extent  a  suction-pump ;  and,  if  so,  the  aspirating 
effect  must  express  itself  on  the  great  veins,  lacking  valves  as 
they  do,  at  their  entrance  into  the  heart ;  hence,  with  each  dias- 
tole the  hlood  would  be  sucked  on  into  the  auricles,  a  result 
that  is  intensified  by  the  respiratory  movements  of  the 
thorax. 

Relative  Time  occupied  by  the  Various  Phases  of  the  Cardiac  Cycle. 
— The  old  and  valuable  diagram  reproduced  below  is  meant  to 
convey  through  the  eye  the  relations  of  the  main  events  in  a 
complete  beat  of   the  heart  or  cardiac  cycle.     The  relative 

length  of  the  sounds ;  the 
long  period  occupied  by  the 
pause ;  the  duration  of  the 
ventricular  systole,  which 
it  is  to  be  observed  is  in 
excess  of  that  of  the  first 
sound,  are  among  the  chief 
facts  to  be  noted. 

The  tracings  of  Chau- 
veau  and  Marey,  obtained 
from  the  heart  of  the  horse, 
which  has  a  very  slow 
rhythm,  show  that  of  the 
whole  period,  the  auricular 
systole  occupies  ^  or  ^-^  of 
a  second  ;  the  ventricular 
systole,  f  or  ^  of  a  sec- 
ond ;  and  the  diastole,  f  or  ^^  of  a  second. 

With  the  more  rapid  beat  in  man  (70  to  80  per  minute),  the 
duration  of  the  cardiac  cycle  may  be  estimated  at  about  j^q-  of 
a  second,  and  the  probable  proportions  for  each  event  are  about 
these:  The  auricular  systole,  ^  of  a  second;  the  ventricular 
systole,  -^  of  a  second ;  and  the  pause,  yV  of  a  second. 

It  will  be  noted  that  the  pause  of  the  heart  is  equal  in  dura- 
tion to  the  other  events  put  together ;  and  even  assuming  that 
there  is  some  expenditure  of  energy  in  the  return  (relaxation) 
of  the  heart  to  its  passive  form,  there  still  remains  a  consider- 
able interval  for  rest,  so  that  this  organ,  the  very  type  of  cease- 
less activity,  has  its  periods  of  complete  repose. 


Fig.  214.  —  Diagram  representing  the  movements 
and  sounds  of  the  heart  during  a  cardiac  cycle 
(after  Sharpey). 


THE   CIRCULATION  OF  THE   BLOOD.  241 

The  Work  of  the  Heart. 

Since  the  pressure  against  "svhich  the  heart  works  must,  as 
we  shall  see,  vary  from  moment  to  moment,  and  sometimes  very 
considerably,  the  work  of  the  heart  must  also  vary  within  wide 
limits,  even  making  allowance  for  large  adaptability  to  the  bur- 
den to  be  lifted ;  for  it  will  be  borne  in  mind  that  the  degree 
to  which  the  heart  empties  its  chambers  is  also  variable. 

If  one  knew  the  quantity  of  blood  ejected  by  the  left  ven- 
tricle, and  the  rate  of  the  beat,  the  calculation  of  the  work 
done  would  be  an  easy  matter,  since  the  former  multiplied  by 
the  latter  would  represent,  as  in  the  case  of  a  skeletal  muscle, 
the  work  of  the  muscles  of  the  left  ventricle ;  from  which  the 
work  of  the  other  chambers  might  be  approximately  calculated. 

The  work  of  the  auricles  must  be  slight,  considering  that  the 
filling  of  the  ventricles  is  not  dependent  solely  upon  their  con- 
traction, that  they  empty  themselves  very  imperfectly,  and 
that  the  tracing  on  Marey's  curves  (Fig.  210),  representing  the 
effect  of  their  contraction  on  the  intraventricular  pressure  is 
but  small.  Notwithstanding,  as  they  largely  determine  by 
their  contraction  and  the  quantity  they  throw  into  the  ventri- 
cles how  full  the  latter  shall  be  in  a  given  instance,  they  really 
have  a  very  large  share  in  determining  the  total  work  of  the 
ventricles  and  the  whole  heart. 

The  right  ventricle,  it  is  estimated  does  from  one  fourth  to 
one  third  the  work  of  the  left ;  not,  of  course,  because  it  throws 
out  less  blood,  for  if  this  were  the  case  the  left  side  of  the  heart 
must  soon  become  empty,  not  to  mention  other  disturbances  of 
the  vascular  equilibrium,  but  because  of  the  relatively  less 
resistance  offered  by  the  pulmonary  vessels. 

All  attempts  to  estimate  exactly  the  quantity  ejected  by  the 
left  ventricle  seem  to  show  that  this  varies  very  greatly,  after 
due  allowance  is  made  for  the  imperfection  of  the  methods  and 
the  great  discrepancies  in  the  results  of  different  observers. 
Perhaps  six  ounces,  or  about  180  grammes,  may  be  taken  as  an 
average  for  the  left  ventricle  of  man.  Assuming  that  his  aortic 
blood-pressure  is,  say  200  mm.  of  mercury  or  3*21  metres  of 
blood,  the  work  of  this  chamber  for  each  beat  would  be  180  X 
3"21,  or  578  gramme-metres.  If  the  heart  beats  seventy  times  per 
minute,  the  wr^rk  for  tin;  day  wcmld  })e  578  X  70  X  GO  X  24  =  58,- 
202,400  gramme-metres.  Or,  upon  the  same  basis,  and  assuming 
that  the  lilood  makes  up  about  the  one  thirteenth  of  the  weight 
of  tlie  individual,  in  a  man  of  14.'J  pounds,  the  whole  of  the 

16 


242  ANIMAL  PHYSIOLOGY. 

blood  would  pass  through  the  heart  in  about  thirty  beats,  or 
in  less  than  half  a  minute. 

When  we  calculate  the  work  done  by  the  heart  for  certain 
intervals,  as  the  day,  the  week,  month,  year,  and  especially  for 
a  moderate  lifetime,  and  compare  this  with  that  of  any  ma- 
chine it  is  within  the  highest  modern  skill  to  construct,  the 
great -superiority  of  the  vital  pump  in  endurance  and  working 
capacity  will  be  very  apparent ;  not  to  take  into  the  account  at 
all  its  wonderful  adaptations  to  the  countless  vicissitudes  of  life, 
without  which  ^t  would  be  absolutely  useless,  even  destructive 
to  the  organism. 

Some  of  these  variations  in  the  working  of  the  heart  we  may 
now  to  advantage  consider. 

Variations  in  the  Cardiac  Pulsation. 

These  may  be  ascertained  either  by  the  investigation  of  the 
arteries  or  of  the  heart,  for  every  considerable  alteration  in  the 
working  of  the  heart  expresses  itself  also  through  the  arterial 
system.  In  speaking  of  the  pulse,  the  reference  is  principally 
to  the  arteries,  but  in  each  case  we  may  equally  well  think  of 
the  heart  primarily  as  acting  upon  the  arteries. 

1.  The  frequency  of  the  heart-beat  varies,  as  might  be  sup- 
posed, with  a  great  multitude  of  conditions,  the  principal  of 
which  are :  age,  being  most  frequent  at  birth,  when  it  may  be 
140  per  minute,  gradually  slowing  to  old  age,  when  it  may  fall 
to  60.  In  feeble  old  age  the  heart-beat  may,  like  many  other  of 
the  functions  of  the  body,  approximate  the  infantile  condition, 
being  very  frequent,  small,  feeble,  and  easily  disturbed  in  its 
rhythm.  ^^ 

It  is  a  matter  of  no  small  importance  to  the  medical  student 
to  be  aware  of  the  normal  rate  for  different  periods  of  life, 
hence  we  give  below  a  pretty  full  statement  of  the  variations 
with  age.  It  will  be  understood  that  the  numbers  are  only  ap- 
proximative, and  that  large  allowance  must  be  made  for  indi- 
vidual deviations : 
At  birth,  130-140     At  4  years,  96-94         At  20  years,  78-72 

lyear,    120-130  5      "       94-90  30      "       75-70 

2  years,  100-110         10      "       90-85  50      "       70-65 

3  "      100-  96         15      "       80-75 

Sex. — The  cardiac  beat  is  more  frequent  in  females  ;  stature, 
more  frequent  in  the  short ;  posture,  most  rapid  in  the  standing 
position,  slower  when  sitting,  and  slowest  in  the  recumbent 


THE  CIRCULATION   OP   THE   BLOOD.  243 

posture ;  season,  more  frequent  in  summer ;  period  of  the  day, 
more  frequent  in  the  afternoon  and  evening ;  elevation  of  tem- 
perature, the  inspiratory  act,  emotions  and  mental  activity,  eating, 
muscular  exercise,  etc.,  render  the  heart-beats  more  frequent. 

2.  The  length  of  the  systole,  though  variable,  is  more  con- 
stant than  that  of  the  diastole.  The  estimated  limits  of  the 
systole  may  be  stated  as  '327  to  'SOI  second. 

3.  The  force  of  the  i^ulsation  varies  very  greatly  and  exer- 
cises an  important  influence  on  the  blood-pressure,  and  the 
velocity  of  the  blood-stream.  As  a  rule,  when  the  heart  beats 
rapidly,  especially  for  any  considerable  length  of  time,  the  force 
of  the  individual  jDulsations  is  diminished. 

4.  The  heart-beat  may  vary  much  and  in  ways  it  is  quite 
possible  to  estimate,  both  directly  by  the  hand  placed  over  the 
organ  on  the  chest,  by  the  modifications  of  the  cardiac  sounds, 
and  by  the  use  of  instruments.  It  is  wonderful  how  much  in- 
formation may  be  conveyed,  without  the  employment  of  any 
instruments,  through  palpation  and  auscultation,  to  one  who 
has  long  investigated  the  heart  and  the  arteries  with  an  intelli- 
gent, inquiring  mind ;  and  we  strongly  recommend  the  student 
to  commence  personal  observations  early  and  to  maintain  them 
persistently. 

Physicians  recognize  the  pulse  (and  heart)  as  "  slow  "  as  dis- 
tinguished from  "  infrequent,"  "  slapping,"  "  heaving,"  "  thrill- 
ing," "bounding,"  etc. 

NoAv,  if  with  these  terms  there  arise  in  the  mind  correspond- 
ing mental  pictures  of  the  action  of  the  heart  under  the  cir- 
cumstances, well ;  if  not,  there  is  a  very  undesirable  blank. 
How  the  student  may  be  helped  to  a  knowledge  of  the  actual 
behavior  of  the  heart  under  a  variety  of  conditions  we  shall 
endeavor  to  explain  later. 

Apart  from  all  the  above  peculiarities,  the  heart  may  cease 
its  action  at  regular  intervals,  or  at  intervals  which  seem  to 
possess  no  definite  relations  to  each  other — that  is,  the  heart 
may  be  irregular  in  its  action,  which  may  be  made  evident 
either  to  the  hand  or  the  ear. 

There  are  certain  deviations  from  tlie  quicker  rhythm  which 
occur  with  such  regularity  and  are  so  dependent  on  events  that 
takes  place  in  other  parts  of  the  body  that  they  may  l)e  con- 
sidered normal.  Reference  will  shortly  bo  made  to  these  and 
the  causes  of  the  variations  enumerated  in  this  section. 

Comparative. — The  following  table  gives  the  mean  number  of 
cardiac  i>ulsations  \Hir  minute  (after  Gamgee)  : 


244 


ANIMAL  PHYSIOLOGY. 


SPECIES. 

Adult. 

Youth. 

Old  age. 

Horse  

36-  40 
46-  50 
45-  50 
70-  80 
70-  80 
90-100 
120-140 

60-  72 

65-  75 

60-  70 

85-  95 

100-110 

110-120 

120-140 

32-  88 

Ass  and  irnile 

55-  60 

Ox 

40-  45 

Sheep  and  goat 

55-  60 

Pig' 

55-  60 

i^^fe • 

Doff 

60-  70 

Cat 

100-120 

The  variations  with,  age,  for  the  horse  and  the  ox,  are  as  fol- 
lows, according  to  Kreutzer : 


Horse. 

At  birth 100-120 

When  14  days  old 80-96 

When  3  months  old 68-76 

When  6  months  old 64-72 

When  1  year  old 48-  56 

When  2  years  old 40-48 

When  3  years  old 38-48 

When  4  years  old 38-50 

When  aged 32-40 


Ox. 

At  birth 92-132 

When  4-5  days  old 100-120 

When  14  days  old 68 

When  4-6  weeks  old 64 

When  6-12  months  old 56-68 

For  the  young  cow 46 

For  the  four-year-old  ox 40 


The  Pulse. 

Naturally  the  intermittent  action  of  the  heart  gives  rise  to 
corresponding  phenomena  in  the  elastic  tubes  into  which  it 
may  be  said  to  be  continued,  for  it  is  very  desirable  to  keep  in 
mind  the  complete  continuity  of  the  vascular  system. 

The  following  phenomena  are  easy  of  observation :  When  a 
finger-tip  is  laid  on  any  artery,  an  interrupted  pressure  is  felt ; 
if  the  vessel  be  laid  bare  (or  observed  in  an  old  man),  it  may 
be  seen  to  be  moved  in  its  bed  forward  and  upward ;  the  press- 
ure is  less  the  farther  the  artery  from  the  heart ;  if  the  vessel 
be  opened,  blood  flows  from  it  continuously,  but  in  spurts ;  if 
one  finger  be  laid  on  the  carotid  and  another  on  a  distant  ves- 
sel, as  one  of  the  arteries  of  the  foot,  it  may  be  observed  (thou^ 
it  is  not  easy,  from  difficulty  in  attending  to  two  events  hap- 
pening so  very  close  together)  that  the  beat  in  the  nearer  ves- 
sel precedes  by  a  slight  interval  that  in  the  more  distant. 

Investigating  the  latter  phenomenon  with  instruments,  it  is 
found  that  an  appreciable  interval,  depending  on  the  distance 
apart  of  the  points  observed,  intervenes. 

What  is  the  explanation  of  these  facts  ? 

The  student  may  get  at  this  by  a  few  additional  observa- 
tions that  can  be  easily  made. 


THE  CIRCULATION  OF  THE  BLOOD. 


245 


If  water  be  seut  through  a  long  elastic  tube  (so  coiled  that 
points  near  and  remote  may  be  felt  at  the  same  time)  by  a  bulb 
syringe,  imitating  the  heart,  and  against  a  resistance  made  by 
drawing  out  a  glass  tube  to  a  fine  point  and  inserting  it  into 
the  terminal  end  of  the  rubber  tube,  an  intermittent  pressure 
like  that  occurring  in  the  artery  may  be  observed ;  and  further 


Fig.  215. — Marej-'s  apparatus  for  showing  the  mode  in  which  the  pulse  is  propagated  in  the 
arteries.  B,  a  rubber  pump,  with  valves  to  prevent  regurgitation.  The  working  of  the 
apparatus  will  be  apparent  from  the  inspection  of  the  figure. 

that  it  does  not  occur  at  precisely  the  same  moment  at  the  two 
points  tested. 

Information  more  exact,  though  possibly  open  to  error,  may 
be  obtained  by  the  use  of  more  elaborate  apparatus,  and  the 
graphic  method. 

Fig.  210  gives  an  idea  of  the  main  features  of  the  pulse-trac- 
ings of  an  arterial  scheme  or  arrangement  of  tubes  in  supposed 
imitation  of  the  conditions  existing  in  the  vascular  system  of 
the  mammalian  body.  Attention  is  especially  directed  to  the 
abrupt  ascent,  the  more  gradual  descent,  and  the  secondary 
waves,  which  are  either  waves  of  oscillation  or  reflex  waves. 

It  may  also  be  noticed  that  the  rise  is  later  as  the  part  of 
the  tube  at  which  it  occurs  is  more  distant  from  the  pump ; 
also  that  it  gets  gradually  less  in  height  and  at  the  same  time 
that  all  the  secondary  waves  are  diminished  or  totally  disap- 
pear; and  with  the  exception  of  the  latter  these  results  hold 
g<^)od  of  the  pulse  in  the  arteries  of  a  living  animal. 

By  measurement  it  has  been  ascertained  that  in  man  the 
puLse- wave  travels  at  the  rate  of  from  five  to  ten  metres  per  sec- 
ond, being  of  course  very  variable  in  velocity.  It  would  seem 
that  the  more  rigid  the  arteries  the  m<^re  rapid  the  rate,  for  in 


246 


ANIMAL  PHYSIOLOGY. 


children  with  their  more  elastic  arteries  the  speed  is  slower ; 
and  the  same  principle  is  supposed  to  explain  the  higher  veloci- 


jn 
0.20  < 


Fig.  316.— Pulse-curves  described  by  a  series  of  sphygmographic  levers  placed  20  cm.  apart 
along  an  elastic  tube  into  which  fluid  is  forced  by  the  sudden  stroke  of  a  pump.  The 
arrows  indicate  the  onward  and  the  reflected  waves.  The  gradual  flattening  and  total  or 
partial  extinction  of  the  waves  are  noteworthy  (after  Marey). 

ty  noticed  in  the  arteries  of  the  lower  extremities.  But  with 
such  a  speed  as  even  five  metres  a  second  it  is  evident  that  with 
a  systole  of  moderate  duration  (say  '3  second)  the  most  distant 
arteriole  will  have  been  reached  by  the  pulse-wave  before  that 
systole  is  completed. 

It  is  known  that  the  blood- current  at  its  swiftest  has  no 
such  speed  as  this,  never  perhaps  exceeding  in  man  half  a  metre 
per  second,  so  that  the  pulse  and  the  blood-current  must  be  two 
totally  distinct  things. 


THE  CIRCULATIOX  OF  THE   BLOOD. 


247 


The  student  may  very  simply  illustrate  this  matter  for  him- 
self. By  tapping  sharply  against  a  pipe  through  which  a 
stream  is  flowing  slowly  and.  quietly,  a  wave  may  be  seen  to 
arise  and  pass  with  considerable  velocity  along  the  moving 
water,  and  with  a  speed  far  in  excess  of  the  rapidity  of  the  main 
current.  When  the  left  ventricle  throws  its  six  ounces  of  blood 
into  vessels  already  full  to  distention,  there  must  be  consider- 
able concussion  in  consequence  of  the  rapid  and  forcible  nature 
of  the  cardiac  systole,  and  this  gives  rise  to  a  wave  in  the  blood 
which,  as  it  passes  along  its  surface,  causes  each  part  of  every 
artery  in  succession  to  respond  by  an  elevation  above  the  gen- 
eral level,  and  it  is  this  which  the  finger  feels  when  laid  upon 
an  artery. 

That  there  is  considerable  distention  of  the  arterial  system 
with  each  pulse  may  be  realized  in  various  ways,  as  by  watch- 
ing and  feeling  an  artery  laid  bare  in  its  course,  or  in  very 
thin  or  very  old  people,  and  by  noticing  the  jerking  of  one  leg 
crossed  over  the  other,  by  which  method  in  fact  the  pulse-rate 
may  be  ascertained.  And  that  not  only  the  whole  body  but 
the  entire  room  in  which  a  person  sits  is  thrown  into  ^'ibration 
by  the  heart's  beat,  may  be  learned  by  the  use  of  a  telescope  to 
observe  objects  in  the  room,  which  may  thus  be  seen  to  be  in 
motion. 

Features  of  an  Arterial  Pulse-Tracing. — In  order  to  judge  of  the 
nature  of  arterial  tracings,  it  is  important  that  the  circum- 
stances under  which  they  are  obtained  should  be  known. 

The  movements  of  the  vessel  wall  in  most  mammals  suit- 


Fio.  217.— Mar^-y's  improved  sphypmoj?raph  arranKfl  for  taking  a  tracing.  ^,  stwl  spring; 
H.  first  l<-v»-r  ;  C,  »Titintf-lt;vt-r  ;  C.  it.s  free  writintf  end  :  I),  screw  for  WxnantR  h  m  con- 
ta/t  with  C:  fi.  slide  with  sinoke<l  i>a|)er ;  //.  cl<K;k-work  :  L.  screw  for  intreasinK  the 
pn-Hsiire  :  .W.  ilial  indieating  tlie  amount  of  pressure  :  K.  K.  straps  for  (Ixint;  rhe  instru- 
Uient  Ui  the  ann,  and  the  latter  to  the  double-inclined  plane  or  .support  (Byroin  Bramwell). 


248 


ANIMAL   PHYSIOLOGY. 


Fig.  218.— Diagrammatic  schema  showing 
the  essential  part  of  the  instrument 
when  in  working  order.  The  knife-edge, 
B" ,  of  the  short  lever  is  in  contact  with 
the  writing-lever,  C.  Every  movement 
of  the  steel  spring  at  A",  communica- 
ted by  the  arteries,  will  be  imparted  to 
the  writing-lever  (Byrom  Bramwell). 


able  for  experiment  and  in  man  is  so  slight  that  it  becomes  ne- 
cessary to  exaggerate  them  in  the  tracing,  hence  long  levers  are 
used  to  accomplish  this. 

The  sphygmograph  is  the  usual  form  of  instrument  em- 
ployed for  the  purpose.  It  consists,  essentially,  of  a  clock-work 
for  moving  a  smoked  surface  (mica  plate  commonly)  on  which 

the  movements  of  a  lever-tip, 
answering  to  those  of  a  button 
placed  on  the  artery,  are  re- 
corded. 

Considering  the  nature  of  the 
pulse  and  the  apparatus  em- 
ployed to  write  its  characters,  it 
will  be  seen  that  the  possible 
sources  of  error  are  numerous. 

Different  observers  have,  as 
a  matter  of  fact,  even  with  the 
same  sort  of  instrument  obtained  tracings  differing  not  a  little 
in  character.  As  the  subjoined  figures  show,  the  pressure  ex- 
erted upon  a  vessel  may  so  alter  the  result  that  entire  features 
of  the  tracing  may  actually  disappear.  The  sphygmograph, 
even  in  the  most  skillful  hands,  has  proved  somewhat  disap- 
pointing as  a  physiological  and  especially  as  a  clinical  instru- 
ment, though  it  is  not  without  a  certain  value. 

We  shall  do  well  to  inquire  whether  there  are  any  features 
in  common  in  tracings  obtained  in  various  ways,  and  which 
have  therefore  in  all  probability  a  real  foundation  in  nature. 

An  inspection  of  a 
large  number  of  pulse- 
tracings,  taken  under 
diverse  conditions, 
seems  to  show  that  in 
all  of  them  there  oc- 
curs, more  or  less 
marked,  the  follow- 
ing :  1.  An  upward 
curve.  2.  A  downward 
curve,  rendered  irreg- 
ular by  the  occurrence 
of  peaks  or  crests  and 
notches.  The  first  of  these  are  termed  the  predicrotic  notch  and 
crest,  and  the  succeeding  ones  the  dicrotic  notch  and  crest. 
The  latter  seem  to  be  the  more  constant. 


Fig.  219.— Pulse-tracing  from  carotid  artery  of  healthy 
man  (after  Moens).  x,  commencement  of  expansion 
of  artery ;  A,  summit  of  first  rise  ;  C,  dicrotic  second- 
ary wave  ;  B,  predicrotic  secondary  wave  ;  p,  notch 
preceding  this  ;  D,  succeeding  secondary  wave.  Curve 
above  is  that  made  by  a  tuning-fork  with  ten  double 
vibrations  in  a  second. 


THE  CIRCULATION  OF  THE  BLOOD. 


249 


That  these  are  genuine,  answer  of  real  and  corresponding 
elevations  of  the  arterial  wall  and  of  the  blood-current  itself, 
seems  probable  from 
the  study  of  a  hcemau- 
iogram.  The  latter  may 
be  obtained  by  allowing 
the  blood  from  a  cut 
artery  to  spurt  against 
a  piece  of  paper  drawn 
in  front  of  the  blood- 
stream. It  is  also  as- 
serted that  by  a  tele- 
phonic connection  with 
an  artery  both  the  pri- 
mary pulse-wave  and 
the  dicrotic  wave  may 
})e  heard.  More  rarely 
there  are  interruptions 
in    the     first     upward 

curve,  termed  anacrotic  curves,  as  distinguished  from  those  in 
the  downward  curve  known  as  katacrotic. 

It  has  been  generally  admitted  that  the  first  marked  upward 

curve  is  due  to  the  systolic 

shock. 

The    following    are,   in 

brief,   some   of   the    views 

that  have  been  entertained 
in  regard  to  the  minor  features  of  the  tracings : 

(a.)  That  the  predicrotic  wave-crest  is  owing  to  the  sudden 
arrest  of  the  flow  from  the  ventricle. 

(b.)  That  the  dicrotic  wave  is  a  wave  of  oscillation. 


Fig.  220.— Piilse-curve  from  radial  of  man.  Taken  with 
an  extra-vascular  pressm^e  of  70  mm.  of  raercm^y. 
The  curved  interrupted  lines  show  the  distance  from 
one  another  in  time  of  the  chief  phases  of  the  pulse- 
wave.  X,  the  commencement,  and  A,  the  close  of  ex- 
pansion of  artery  ;  p,  predicrotic  notch  ;  d,  dicrotic 
notch  ;  C,  dicrotic  crest ;  D,  post-dicrotic  crest ;  /, 
the  post-dicrotic  notch. 


Zai. — Anacrotic  pulse-tracing  from  carotid  of 
rabbit. 


F'lO.  222. — Two  grade.s  of  marked  dicrotLsm  in  radial  pulse  of  man  (typhoid  fever). 

(c.)  That  it  is  a  wave  of  reflection  from  the  periphery. 

(d.)  That  it  is  caused  by  the  sudden  closure  of  th(i  aortic 
valves. 

It  appears  to  be  now  pretty  well  agreed  that  the  the(jry  of 
r(*fl(;ction  is  untenable  on  physical  principles;  that  a  high 
blood-pressure   tends  to  render  the  katacrotic  markings   less 


250 


ANIMAL   PHYSIOLOGY. 


distinct,  and  the  reverse  when  the  pressure  is  low,  as  after 
hsemorrhages.      These  features  are   especially  marked  in  the 


Fig.  224.— Anacrotic  sphyg- 
mograph  tracing  from 
the  ascending  aorta  in  a 
case  of  aneruism. 


:^ :^ 

Fig.  223.— Normal  pulse-curve  in  the  aorta  from  the  dog. 

dicrotic  pulse  of  fever,  etc.,  when  the  blood-pressure  is  low  and 
may  be  recognized  even  by  the  hand.     The  anacrotic  crests 
and  notches  are  abnormal,  and  probably 
due  to  excessive  rigidity  of  the  arteries. 

Certain  it  is  that,  without  any  change 
in  the  heart-beat,  changes  in  the  tracings 
may  arise,  owing  to  modifications  in  the 
periphery  of  the  vascular  system.  We  do 
not  propose  to  discuss  the  above-men- 
tioned views  of  the  causation  of  the  minor 
features  of  the  tracings  in  detail,  about 
which  the  greatest  differences  of  opinion 
still  prevail.  Even  if  all  the  characteristics  of  an  arterial 
tracing  could  be  ob- 
tained from  an  arti- 
ficial schema,  it 
would  not  follow 
that  the  conditions 
in  each  case  were 
the  same  ;  in  fact, 
as  we  view  the  mat- 
ter, it  would  be  all 
but  impossible  that 
such  should  be  the 
case. 

Rubber  tubes  are 
not  comparable  to 
arteries ;  and  espe- 
cially not  to  arteri- 
oles and  capillaries. 
Bearing  in  mind  the 
peculiar  nature  of  the  blood-corpuscles;  their  relation  to  the 
walls  of  the  vessels  in  which  they  flow;   the  relation  of  the 


Fig.  225.— Influence  of  changes  in  the  pressure  applied  to 
the  exterior  of  the  vessel  (extra-vascular)  on  the  form  of 
the  curve,  a,  from  the  radial  of  a  man  of  twenty-seven 
years,  with  an  extra-arterial  pressure  of,  in  a,  70  mm., 
in  a',  to  50  mm.,  and  in  a",  to  30  mm.  mercury. 


THE  CIRCULATION   OF  THE   BLOOD.  251 

blood  to  the  nutrition  of  the  tissues ;  the  fact  that  all  the  tubes 
that  compose  the  vascular  system  are  made  up  of  living  cells ; 
that  some  of  these 
cells  (in  arterioles  and 
capillaries)  are  in  a 
semi-fluid  condition — 
in  a  word,  that  the 
conditions  of  the  cir- 
culation  as    a   whole 

■1  Fig.  226. — Dicrotic  pulse-curve  clue  to  hieinorrha^e.    From 

are      sin     generis,     be-  carotid  of  rabWt,  wnth  extra- vascular  pressure  of,  in  a, 

P  ,  1      .         -J.    I'i.  50  mm.,  b,  of  40  mm.,  c,  of  20  mm.,  and  d,  of  10  mm. 

cause  OI  tneir  vitality  mercury.    (This  and  the  preceding  six  tracings  from 

•  i                    I  Foster.) 

— it  seems  to  us  amaz- 
ing that  purely  physical  explanations,  such  as  would  answer 
for  a  pump  and  set  of  rubber  tubes,  should  ever  have  been 
deemed  satisfactory.  The  whole  subject  seems  to  be  involved 
in  a  gross  misconception,  and  should  be  regarded,  we  must 
think,  from  an  entirely  new  standpoint. 

Venous  Pulse. — Apart  from  the  variations  in  the  caliber  of 
the  great  veins  near  the  heart,  constituting  a  sort  of  pulse, 
though  due  to  variations  in  intra-cardiac  pressure,  a  venous 
pulse  proper  is  rare  as  a  normal  feature.  One  of  the  best- 
known  examples  of  such  occurs  in  the  salivary  gland.  When, 
during  secretion,  the  arterioles  are  greatly  dilated,  a  pulse  may 
be  witnessed  in  the  veins  into  which  the  capillaries  open  out, 
owing  to  diminution  in  the  resistance  which  usually  is  suffi- 
ciently great  to  obliterate  the  pulse-wave. 

Pathological. — In  severe  cases  of  heart-disease,  owing  to 
cardiac  dilatation  or  other  conditions,  giving  rise  to  incompe- 
tency of  the  tricuspid  valves,  there  may  be  with  each  ventricu- 
lar systole  a  back-flow,  visible  in  the  veins  of  the  neck. 

A  venous  jjulse  is  a  phenomenon,  it  will  be  evident,  that 
always  demands  special  investigation.  It  means  that  the  usual 
bounds  of  nature  are  for  some  good  reason  being  over-stepped. 

Comparative. — Before  entering  on  the  consideration  of  phe- 
nomena that  all  are  agreed  are  purely  vital,  we  call  attention  to 
the  circulation  in  forms  lower  than  the  mammal,  in  order  to 
give  breadth  to  the  student's  views  and  prepare  him  for  the 
special  investigations,  which  must  be  referred  to  in  subsequent 
chapters ;  and  which,  owing  to  the  previous  narrow  limits  (re- 
searches upon  the  frog  and  a  few  well-known  mammals)  having 
at  last  been  overleaped,  have  opened  up  entirely  new  asfxHits  of 
cardiac  physiology — one  might  almost  say  revolutionized  the 
subject. 


252  ANIMAL  PHYSIOLOGY^ 

Owing  to  the  limitations  of  our  space,  the  references  to  lower 
forms  must  be  brief. 

We  recommend  the  student,  however,  to  push  the  subject 
further,  and  especially  to  carry  out  some  of  the  experiments  to 
which  attention  will  be  directed  very  shortly. 

In  the  lowest  organisms  (Infusorians)  represented  by  Amoe- 
ba, Vorticella,  etc.,  there  are,  of  course,  no  circulatory  organs, 
unless  the  pulsating  vacuoles  of  some  forms  mark  the  crude 
beginnings  of  a  heart.  It  will  be  borne  in  mind,  however,  that 
there  is  a  constant  streaming  of  the  protoplasm  itself  within 
the  organism. 

Among  Coelenterates  (Figs.  254, 355)  the  digestive  system,  as 
yet  but  imperfectly  developed,  seems  to  embody  in  itself  a  sort 
of  combination  of  the  functions  of  the  preparation  and  distribu- 
tion of  elaborated  food ;  and  it  is  worth  while  to  note  that  even 
in  the  highest  animals  the  digestive  tract  remains  in  close  con- 
nection with  the  circulatory  system. 

The  heart  is  first  represented,  as  in  worms,  by  a  pulsatile 
tube,  which  may,  as  in  the  earth-worm,  extend  throughout  the 
greater  part  of  the  length  of  the  animal,  and  has  usually  dorsal 
and  ventral  and  transverse  connections. 

The  dilatations  of  the  transverse  portions  in  one  division 
(metamere)  of  the  animal  seem  to  foreshadow  the  appearance  of 
auricles. 

The  pulsation  of  the  dorsal  vessel  in  a  large  earth-worm  is 
easy  of  observation. 

In  the  mollusks  the  heart  consists  of  a  ventricle  and  one  or 
more  auricles,  and  these  chambers  give  off  and  receive  large 
vessels  (Fig.  327). 

These  hearts  may  be  observed  pulsating  with  the  naked  eye 
or  a  lens  in  the  clam,  oyster,  or  snail,  and  are  to  be  looked  for 
in  the  first  two  on  the  side  of  the  animal  toward  the  hinge  of 
the  shell. 

It  is  worthy  of  note  that  in  cephalopod  mollusks  (Cuttle- 
fish, Poulpe)  there  are  branchial  hearts,  which  may  be  re- 
garded in  the  light  of  pulsatile  venous  expansions,  a  remnant, 
perhaps,  of  conditions  found  in  lower  forms,  in  which  we  have 
seen  that  the  rhythmically  contracting  tube  plays  a  prominent 
role. 

In  amphioxus,  which  is  often  instanced  as  the  lowest  verte- 
brate, the  blood-vessels,  including  the  portal  vein,  are  pulsatile, 
while  there  is  no  distinct  and  separate  heart ;  but,  in  connection 
with  the  above  observations  in  cephalopods,  it  is  to  be  re- 


THE   CIRCULATION  OP  THE  BLOOD. 


253 


marked  that  in  this  creature  there  are  contractile  dilatations  at 
the  bases  of  the  branchial  arteries. 


Fig.  227.— Circulatory  and  excretory  organs  of  the  cuttle-fish  (Sepia  officinalis),  viewed  from 
the  dorsal  side  (after  Hunter).  Br,  gills  ;  C,  ventricle  ;  Ao  and  Ao\  anterior  and  poste- 
rior aorta  ;  V.  lateral  vein  ;  Ft'',  anterior  vena  cava  ;  Vc".  posterior  vena  cava  :  N,  renal 
appendages  of  the  veins  ;  Vlr,  advehent  branchial  vessels  (branchial  arteries) ;  Kh, 
branchial  heart ;  Ap,  appendage  of  the  same  ;  At,  At',  auricles  receiving  the  revehent 
branchial  vessels  (brancnial  veins). 


In  some  Ascidians  the  heart  is  of  a  somewhat  crescentic 
form,  and  has  the  remarkable  property  of  beating  for  a  time  in 
one  direction,  then  stopping  and  reversing  its  rhythm.  In  a 
transparent  specimen,  under  the  microscope,  this  can  be  seen 
admirably. 

In  the  crab  the  heart  lies  within  a  pericardium,  loosely  at- 
tached, the  main  vessels  being  connected  with  the  pericardium 
and  not  directly  with  the  heart.  The  heart  sucks  its  blood 
from  the  pericardial  cavity  through  four  valvular  openings. 

In  such  a  creature  as  the  scorpion  there  is  a  chambered 
heart,  with  a  division  for  each  principal  segment  of  the  animal's 
body  (Fig.  308). 

While  in  mollusk.s,  crustaceans,  and  other  groups,  the  vas- 
cular system  does  not  form  a  connected  whole,  the  scorpion  is 
exceptionally  advanced  in  this  respect,  being  provided  with 
capillaries,  or  tuVjes  closely  representing  them.  Among  most 
of  the  invertebrates  the  blood,  after  leaving  the  arteries,  passes 
into  rather  wide,  irregular  spaces  among  the  various  tissues, 
from  which  it  is  taken  up  by  the  veins  without  the  intervention 
of  an  int(;rmediate  sot  of  vosseLs. 

The  circulatory  system  of  an  insect  or  crustacean  may  be 


254 


ANIMAL  PHYSIOLOGY. 


viewed  microscopically  in  aquatic  forms,  which  are  often  quite 
transparent,  especially  in  the  larval  condition. 


S-3  frl  ^  3 

".,_o 


(N'S,'^  c3  C  o 
oj.if  tS  s-  3  ti 


Although  the  respiratory  system  will  be  treated  from  the 
comparative  point  of  view,  the  student  will  do  well  to  note  now 


THE  CIRCULATION  OF  THE  BLOOD. 


255 


Ba      r  Pc  I 

Fig.  229.— Diagrram  of  the  circulation  of  a  Teleostean  fish  (Claus).  V,  ventricle  ;  Ba,  bulbus 
arteriosus,  with  the  arterial  arches  which  carry  the  blood  to  the  gills  ;  Ab.  arterial  arches  ; 
Ao,  aorta  descendens,  into  which  the  epibranchial  arteries  passing  out  from  the  gills 
unite  ;  A',  kidneys  ;  /,  intestine  ;  J'c,  portal  circulation. 

(in  the  figures)  the  close  relation  between  the  organs  for  dis- 
tributing and  aerating  the  blood. 


Fio.  230. 


Fig.  231. 


Fio.  230.— The  arterial  trunks  and  their  main  branches  in  the  frog  (Rana  escnlenta).  1  x  IJ. 
(Howes.  I  i,  lingual  ve8.sel ;  c.  c,  common-carotid  artery  ;  p.  cu,  pulmo-cutaneous  artery  ; 
c.  gl.  carotid  gland  ;  au',  right  auricle  ;  au",  left  auricle  ;  v.  ventricle  ;  tr.  a,  truncus  ar- 
terifjKus  ;  p?ii',  pulmonary  ;  If/",  left  lung  ;  ao'  ,  left  aortic  arch  ;  for,  brachial ;  en.  cuta- 
neous ;  d.  no,  dorsal  aorta ;  ctit.  creliaco-mesenteric  ;  ai''.  creliac  ;  lip,  hepatic  ves.sel8  ; 
fj.  gastric  ;  pc'.  pancreas  ;  m,  mesenteric ;  «p,  splenic  ;  du',  duodenal ;  h,  hfemorrhoidal ; 
il',  ileal  ;  hy.  hypogastric  ;  c.  il.  common-ih'ac  ;  re,  renal  ;  k,  kidney  ;  ts,  spermatic. 

Fig.  231.— Venous  trunks  and  their  main  branches  in  the  frog  {Rana  CKCtilcnta).  1  x  ]J. 
(Howes.)  /,  lingual  vein;  p.J,  external  jugular;  in,  innominate;  i.J,  internal  jugular; 
n.  Kc,  subsfiapular  ;  pr.  c,  vena  cava  superior  ;  h.  v,  sinus  venosus  ;  hp,  hepatic  ;  lv\  right 
lobe  of  liver  ;  Iv".  left  lobe  of  liver  ;  pt.  r.  vena  cava  inferior  ;  ov.  ovarian  ;  d.  I,  dorso- 
lurnbar  ;  od.  ovlflucal  ;  r.p,  renal-portal;  fin,  femoral:  hc,  sciatic;  «,  feinoro  sciatic 
anastomosis  ;  pv',  right  jk-IvIc  ;  vn,  vesical  ;  tint,  ah,  anterior  abdominal  ;  a',  abdominal- 
I>ortal  anastomosis  ;  il' .  ileal  ;  np,  splenic  ;  du',  duodenal  ;  I.  int,  lieno-intestliial  ;  y,  gas- 
trie  ;  J),  portal ;  /y",  left  lung  ;  jnd,  pulmonary  ;  m.  cu,  niusculo-cutaueous  ;  br,  brachial. 


'256 


ANIMAL   PHYSIOLOGY. 


Passing  on  to  the  vertebrates,  in  the  lowest  group,  the  fishes, 
the  heart  consists  of  two  chambers,  an  auricle  and  a  ventricle, 
the  latter  being  supplemented  by  an  extension  (buTbus  arterio- 
sus) pulsatile  in  certain  species;  and  an  examination  of  the 
course  of  the  circulation  will  show  that  the  heart  is  through- 
out venous,  the  blood  being  oxidized  in  the  gills  after  leaving 
the  former. 

Among  the  amphibians,  represented  by  the  frog,  there  are 
two  auricles  separated  by  an  almost  complete  septum,  and  one 


Fig.  233. 


Fig   233. 


Fig.  232. — The  frog's  heart,  seen  from  the  front,  the  aortic  arches  of  the  left  side  having  been 

removed.    (1  x  4.)    ca,  carotid  ;  c.  gl,  carotid  gland  ;  ao,  aorta  ;  au',  right  auricle  ;  au". 

left  auricle  ;  pr.  c,  vena  cava  superior  ;  p^.  c.  vena  cava  inferior  ;  p.  cu,  pulmo-cutaneous 

trunk  ;  ^^,  truncus  arteriosus  ;  v,  ventricle  (Howes). 
Fig.  233.— The  same,  seen  from  behind,  the  sinus  venosus  having  been  opened  up  to  show  the 

slnu-auricular  valves.    (1  x  4.)    p.  v.  pulmonary  vein  ;  s.v,  sinus  venosus  ;  va",  sinu-au- 

ricular  valve.    Other  lettering  as  in  Fig.  232  (Howes). 

ventricle  characterized  by  a  spongy  arrangement  of  the  mus- 
cle-fibers of  its  walls. 

In  the  reptiles  the  division  between  the  auricles  is  complete, 
and  there  is  one  ventricle  which  shows  imperfect  subdivisions. 

In  the  crocodile,  however,  the  heart  consists  of  four  per- 
fectly divided  chambers.  Of  the  two  aortic  arches,  one  arises 
together  with  the  pulmonary  artery  from  the  right  ventricle, 
and,  as  it  crosses  over,  the  left  communicates  with  it  by  a  small 
opening,  so  that,  although  the  arterial  and  the  venous  blood 
are  completely  separated  in  the  heart,  they  intermingle  outside 
of  this  organ. 

In  birds  the  circulatory  system  is  substantially  the  same  as 
in  mammals ;  but  in  all  vertebrate  forms  below  birds  the  blood 
distributed  to  the  tissues  is  imperfectly  oxidized  or  is  partially 
venous. 


THE  CIRCULATION   OF   THE   BLOOD. 


257 


As  an  example  of  the  influence  of  valves  and  of  blood-press- 
ure on  the  distribution  of  the  blood  we  may  take  the  case  of  the 
turtle,  in  which  the  subject  has  been  most  carefully  studied. 


Fig.  2:U. 


Fig.  :i35. 


Fig.  234.— The  heart,  dissected  from  the  front,  the  ventral  wall  and  one  of  the  aurieulo-ven- 
tricular  valves  having  been  removed.  (1  x  6.)  The  rod,  passin;^  from  the  ventricle  into 
the  i)ylangiuni,  shows  the  course  taken  by  the  blood  flowing  into  the  carotid  and  aortic 
trunks,  sy,  synangium  ;  p.  v\  aperture  of  entry  of  pulmonary  vein  ;  va'\  sinu-auricular 
valve  ;  «.  .v,  inter-auricular  septum  ;  ra'.  aiiriculo-ventricular  valve  ;  va.  s.  semi-lunar 
valves  :  jjij.  pylangium  :  ra.  I.  longitudinal  valve  (septum)  of  pylangium  ;  p.  cu'.  point  of 
origin  of  pulmn-cutaneous  trunk  (Ho\v('.«.) 

Fig.  23.5. —Heart  and  arteries  of  a  reptile  (hoai.  r,  right,  and  I,  left  auricle  ;  c,  carotid  artery; 
ra.  right  aortic  arch  ;  la,  left  aortic  arch  ;  p,  pulmonary  artery  ;  rv,  right  vena  cava  ;  Iv, 
left  vena  cava  superior  ;  vi.  vena  cava  inferior.  The  arrows  indicate  the  course  of  the 
circulation  i  after  Gegeubaur). 


The  structure  of  the  heart  and  the  relations  of  its  main  ves- 
sels, etc.,  will  probably  be  sufficiently  clear  upon  an  examina- 
tion of  the  accompanying  figures  and  the  descriptions  beneath 
them. 

The  right  and  left  auricles  pour  their  blood,  kept  somewhat 
apart  by  valves,  into  the  eavum  venosum. 

Two  arterial  arches  arise  from  the  right-hand  part  of  this 
region,  while  the  pulmonary  artery  is  a  branch  carrying  off 
blood  to  the  lungs  from  the  cnvum  puhnnup.  No  vessels  arise 
from  the  f-avum  arteriosum. 

Since  the  blood  flows  in  the  direction  of  least  resistance 
when  the  ventricle  contracts,  the  venous  blood  of  the  cavum 
venosum  passes  on  into  the  pulmonary  artery  in  which  the 
pressure  is,  of  course,  lower  tlian  in  tlic  aortic  arches,  but,  as 
the  systoh;  f:ontinues, the  arterial  ldo(jd  of  the  cavum  arterio- 
17 


258 


ANIMAL  PHYSIOLOGY. 


sum  crowds  on  the  venous  blood,  and  passes  itself  with,  some  of 
the  darker  blood  into  the  aortic  vessels,  in  which  the  arrange- 


BAih 


Fig.  236. 


Fig.  237. 

Fig.  236.— Heart  and  arteries  of  a  turtle  (Chelydrd).  rp,  right  pulmonary,  and  Zp,  left  pul- 
monary artery  ;  other  letters  the  same  signification  as  in  the  previous  figure  (after  Gegen- 
baur). 

Fig.  237. — Heart  of  a  turtle  {Chelone  midas).  A.  Drawing  from  nature,  the  ventral  face  of 
the  ventricle  being  laid  open.  B.  Diagram  explanatory  of  the  circulation.  Everywhere 
the  arrows  indicate  the  course  the  blood  takes.  R.  A.,  L.  A.,  right  and  left  auricles. 
V,  the  right,  w',  the  left  median  auriculo-ventricular  valves.  C.  v,  cavum  venosum.  C.  p, 
cavum  pulmonale,  a,  the  incomplete  septum  which  divides  the  cavum  pulmonale  from 
the  rest  of  the  cavity  of  the  ventricle.  P.  A,  pulmonary  artery.  R.  Ao,  L.  Ao,  right  and 
left  aortse  (after  Huxley). 

ment  of  the  valves  assists  materially.  Note  that,  as  the  systole 
advances,  the  imperfect  septum  between  the  cavum  pulmonum 
and  cavum  venosum  approaches  the  back  of  the  heart  wall,  and 
thus  tends  to  shut  off  the  cavum  pulmone  from  the  purer  blood. 

As  a  result  of  the  entire  arrangement,  the  least  oxidized 
blood  passes  to  the  lungs,  and  the  most  aerated  to  the  head  and 
anterior  parts  of  the  animal. 

In  the  frog  and  other  creatures,  with  three  imperfectly  sepa- 
rated heart  cavities,  a  similar  result  is  attained. 

The  resemblances  in  such  cases  to  the  foetal  conditions  in 
mammals,  including  man,  will  be  apparent,  and  it  is  especially 


THE  CIRCULATION  OF  THE   BLOOD.  259 

to  be  observed  that  in  the  case  of  the  foetus  and  these  lower 
groups  of  vertebrates  the  brain  and  anterior  parts — that  is, 
the  most  important  portions  of  the  animal  functionally, 
the  parts  on  which  the  rest  depend  for  their  well-being  (since 
the  brain  is  the  seat  of  all  the  main  directive  centers) — are 
fed  with  the  best  blood  the  organism  possesses,  a  fact  which 
probably  explains  in  part  the  relatively  large  size  of  these 
portions  of  the  body  early  in  foetal  life  and  throughout  its 
duration. 

We  now  urge  upon  the  student  the  importance  of  making 
some  observations  for  himself  upon  the  heart  of  the  frog,  tur- 
tle, snake,  fish,  or  other  of  the  cold-blooded  animals.  At- 
tention should  be  given  chiefly  to  the  functions  of  the  heart, 
though  to  do  this  intelligently  it  must  be  preceded  by  some 
study  of  the  anatomy  of  the  organ.  It  will  be  understood  that 
any  directions  we  may  give  for  the  manipulative  part  of  the 
work  will  be  of  the  simplest  kind,  and  rather  suggestive  of  the 
general  method  of  procedure  than  intended  to  illustrate  the 
best  methods. 

In  reality,  it  is  better  for  exact  investigation  of  the  heart 
that  no  anaesthetic  be  given,  and  an  animal  may  be  rendered 
insensible  by  a  sudden  blow  upon  the  head,  which,  as  we  shall 
show  later,  may  be  painless.  However,  it  will  be,  upon  the 
whole,  perhaps,  best  that  the  animal  be  given  a  few  whiffs  of 
ether  beneath  some  (glass)  vessel,  and  as  soon  as  it  becomes 
insensible,  to  withdraw  the  anaesthetic,  remove  or  crush  the 
head  (brain),  so  that  throughout  the  investigation  there  may 
be  neither  interference  with  the  heart  from  this  organ  nor  any 
doubt  about  the  animal's  insensibility. 

It  is  well  to  open  the  abdomen  a  little  below  the  heart,  so 
that  the  latter  may  be  exposed,  with  its  pericardium  intact, 
when  the  relations  of  the  heart  to  the  surrounding  parts  may 
be  noticed. 

What  strikes  every  observer  is  the  sluggish  action  of  the 
hearts  of  these  animals — a  great  advantage  in  attempting  to 
estimate  roughly  the  relative  time  occupied  by  the  systole  and 
diastole  of  tlie  different  chambers;  the  peculiar  vermiform 
nature  of  the  contraction ;  the  changes  of  color  dependent  on 
the  degree  to  which  any  chamber  is  filled  with  blood;  and 
many  of  those  minor  details  important  in  making  u])  a  total 
general  impression,  but  not  readily  (expressed  in  words." 

After  the  animal  has  been  bled,  the  heart's  action  may  still 
be  profitably  studi(jd ;  and,  finally,  it  may  be  learned  that  the 


260  ANIMAL  PHYSIOLOGY. 

heart  will  pulsate  when  removed,  either  entire  or  after  being 
divided  into  sections. 

In  another  specimen  it  would  be  desirable  to  allow  the 
heart,  to  be  kept  bathed  in  serum  or  physiological  saline  solu- 
tion, to  beat  as  long  as  it  will,  and  to  note  the  various  phases 
of  irregularity,  weakening,  and  cessation  of  action  in  its  dif- 
ferent parts. 

It  is  also  highly  instructive  to  observe  the  eif ect  of  ligating 
oif  certain  of  the  chambers  from  the  rest  of  the  organ. 

Any  one  who  makes  a  few  such  observations  will  be  pre- 
pared to  comprehend  readily  any  of  the  experiments  on  the 
hearts  of  the  cold-blooded  animals,  and  w^U  be  able,  especially 
if  he  has  followed  out  earlier  recommendations  as  to  the  study 
of  the  heart  of  the  mammal,  to  form  a  mental  picture  of  what 
is  transpiring  within  his  own  breast,  which  is  one  of  the  most 
desirable  accomplishments — in  fact,  the  best  test  of  real  knowl- 
edge. 

Whatever  ground  for  differences  of  opinion  there  may  be 
as  to  the  extent  to  which  the  phenomena  we  have  as  yet  been 
describing  are  mechanical  in  their  nature,  all  are  agreed  that 
such  explanations  are  insufficient  when  applied  to  the  facts 
with  which  we  have  yet  to  deal.  They,  at  all  events,  can  be 
regarded  only  as  the  result  of  vitality. 

When  one  reflects  upon  the  vicissitudes  through  which  an 
animal  must  pass  daily  and  hourly,  necessitating  either  that 
they  be  met  by  modified  action  of  the  organs  of  the  body  or 
that  the  destruction  of  the  organism  ensue,  it  becomes  clear 
that  the  varying  nutritive  needs  of  each  part  must  be  met  by 
changes  in  the  circulatory  system.  These  changes  may  affect 
any  part  of  the  entire  arrangement,  and  it  rarely  happens,  as 
will  appear,  that  one  part  is  modified  without  a  correspond- 
ing one,  very  frequently  of  a  different  kind,  taking  place  in 
some  other.  What  these  various  correlated  modifications  are, 
and  how  they  are  brought  about,  we  shall  now  attempt  to 
describe,  and  it  will  greatly  assist  in  the  comprehension  of  the 
whole  if  the  student  will  endeavor  to  keep  a  clear  mental  pict- 
ure of  the  parts  before  his  mind  throughout,  using  the  figures 
and  verbal  descriptions  only  to  assist  in  the  construction  of 
such  a  mental  image.  We  shall  begin  with  the  vital  pump — 
the  heart. 


THE  CIRCULATION   OF   THE   BLOOD.  261 

The  Beat  of  the  Heart  and  its  Modifications. 

As  lias  been  already  noted,  the  cardiac  muscle  lias  features 
peculiar  to  itself,  and  occupies  histologically  an  intermediate 
place  between  the  plain  and  the  striped  muscle-cells,  and  that 
the  contraction  of  the  heart  is  also  intermediate  in  character, 
and  is  best  seen  in  those  forms  of  the  organ  which  are  some- 
what tubular  and  beat  slowly.  But  the  contraction,  though 
peristaltic,  is  more  rapid  than  is  usually  the  case  in  other 
organs  with  the  smooth  form  of  muscle-fiber. 

The  heart  behaves  under  a  stimulus  in  a  peculiar  manner. 
The  effect  of  a  single  induction  shock  depends  on  the  phase  of 
contraction  in  which  the  heart  is  at  the  moment  of  its  applica- 
tion. Thus  at  the  commencement  of  a  systole  there  is  no  visi- 
ble effect,  while  beats  of  unusual  character  result  at  other 
times.  But  tetanus  can  not  be  induced  by  any  form  or  method 
of  stimulation.     The  latent  period  of  cardiac  muscle  is  long. 

In  a  heart  at  rest  a  single  stimulus  (as  the  prick  of  a  needle) 
usually  calls  forth  but  one  contraction. 

The  Nervous  System  in  Relation  to  the  Heart. 

The  attempts  to  determine  just  why  the  heart  beats  at  all, 
and  especially  the  share  taken  by  the  nervous  system,  if  any 
direct  one,  are  beset  with  great  difficulty ;  though,  as  we  shall 
attempt  to  show  later,  this  subject  also  has  been  cramped  within 
too  narrow  limits,  and  hence  regarded  in  a  false  light. 

Till  comparatively  recently  the  frog's  heart  alone  received 
much  attention,  if  we  except  those  of  certain  well-known  mam- 
mals. In  the  heart  of  the  frog  there  are  ganglion-cells  in  vari- 
ous parts,  especially  numerous  in  the  sinus  venosus  (or  expan- 
sion of  the  great  veins  where  they  meet  the  auricles) ;  also  in 
the  auricles,  more  especially  in  the  septum  (ganglia  of  Remak), 
while  they  are  absent  from  the  greater  part  of  the  ventricle, 
though  found  in  the  auriculo-ventricular  groove  (ganglia  of 
Bidder). 

Recently  it  has  been  found  that  ganglion-cells  occur  in  the 
ventricles  of  warm-blood  animals.  In  the  hearts  of  the  dog, 
calf,  sheep,  and  pig,  which  are  those  lately  subjected  to  investi- 
gation, it  is  found  tliat  the  nerve-cells  do  not  occur  near  the 
apex  of  the  ventricles,  but  mainly  in  the  middle  and  basal  por- 
tions, being  most  abundant  in  the  anterior  and  ])osterior  inter- 
ventricular furrows  and  in  the  left  ventricle.     But  there  are 


262  ANIMAL  PHYSIOLOGY. 

differences  for  each  group  of  animals;  thus,  these  ganglion- 
cells  are  most  abundant,  so  far  as  the  mammals  as  yet  inves- 
tigated are  concerned,  in  the  ventricles  of  the  pig,  and  least  so 
in  those  of  the  dog.  In  the  cat  they  are  also  scanty.  Ganglion- 
cells  occur  in  the  auricles,  and  are  especially  abundant  near  the 
terminations  of  the  great  veins. 

It  has  long  been  known  that  the  heart  of  a  frog  removed 
from  the  body  will  pulsate  for  hours,  especially  if  fed  with 
serum,  blood,  or  similar  fluids ;  and  that  it  may  be  divided  in 
almost  any  conceivable  way,  even  when  teased  up  into  minute 
particles,  and  still  continue  to  beat.  The  apex,  however,  when 
separated  does  not  beat.  Yet  even  this  quiescent  apex  may  be 
set  pulsating  if  tied  upon  the  end  of  a  tube,  through  which  it 
may  be  fed  under  pressure. 

We  may  here  point  out  that  the  whole  heart  or  a  part  of  it 
may  be  made  to  describe  its  action  by  the  graphic  method  in 
various  ways,  the  principles  underlying  which  are  either  that 
the  heart  pulls  upon  a  recording  lever  (lifts  it)  acts  against  the 
fluid  of  a  manometer ;  or,  inclosed  in  a  vessel  containing  oil  or 
similar  fluid,  moves  a  piston  in  a  cylinder. 

It  has  also  long  been  known  that  a  ligature  drawn  around 
the  sinus  venosus  (in  the  frog)  at  its  junction  with  the  auricles 
stopped  the  heart  for  a  certain  period,  and  this  experiment  (of 
Stannius)  was  thought  to  demonstrate  that  the  heart  was  ar- 
rested because  the  nervous  impulses  proceeding  to  the  ganglion- 
cells  along  the  cardiac  nerves  or  ganglia  of  this  region  were 
cut  off  by  the  ligature ;  in  other  words,  the  heart  ceased  to  beat 
because  the  outside  machinery  on  which  the  action  of  the  inner 
depended  was  suddenly  disconnected.  Other  explanations  have 
been  offered  of  this  fact. 

Within  the  last  few  years  great  light  has  been  thrown  upon 
the  whole  subject  of  cardiac  physiology  in  consequence  of  in- 
vestigators having  studied  the  hearts  of  various  cold-blooded 
animals  and  of  several  invertebrates.  The  hearts  of  the  Clie- 
lonians  (tortoises,  turtles)  have  received  special  attention,  and 
their  investigation  has  been  fruitful  of  results,  to  the  general 
outcome  of  which,  as  well  as  those  accruing  from  recent  com- 
parative studies  as  a  whole,  we  can  alone  refer. 

Very  briefly,  the  following  are  some  of  the  main  facts : 

1.  In  all  cold-blooded  animals  the  order  in  which  the  sub- 
divisions of  the  heart  cease  to  pulsate  when  kept  under  the 
same  conditions  is  invariable,  viz.,  ventricle,  auricles,  sinus. 

2.  The  sinus  and  auricles,  when  separated  by  section,  liga- 


THE  CIRCULATION  OF   THE   BLOOD.  263 

ture,  or  otherwise,  either  together  or  singly,  continue  to  beat, 
whether  amply  provided  with  or  surrounded  by  blood. 

3.  The  ventricle  thus  separated  displays  less  tendency  to 
beat  independent  of  some  stimulus  (as  feeding  under  pressure), 
though  a  very  weak  one  usually  suffices — i.  e.,  its  tendency  to 
spontaneous  rhythm  is  less  marked  than  is  the  case  with  the 
other  parts  of  the  heart.  These  remarks  apply  to  the  hearts 
of  Chelonians — fishes,  snakes,  and  some  other  cold-blooded 
animals. 

4.  In  certain  fishes  (skate,  ray,  shark)  the  beat  may  be  re- 
versed by  stimulation,  as  a  prick  of  the  ventricle.  This  is 
accomplished  with  more  difficulty  in  other  cold-blooded  animals, 
and  still  more  so  in  the  mammal. 

5.  In  certain  invertebrates,  notably  the  Poulpe  (Octopus),  a 
careful  search  has  revealed  no  nerve-cells,  yet  their  hearts  con- 
tinue to  beat  when  their  nerves  are  severed,  on  section  of 
parts  of  the  organ,  etc. 

6.  A  strip  of  the  muscle  from  the  ventricle  of  the  tortoise, 
when  placed  in  a  moist  chamber  and  a  current  of  electricity 
passed  through  it  for  some  hours,  will  commence  to  pulsate  and 
continue  to  do  so  after  the  current  lias  been  withdrawn ;  and 
this  holds  when  the  strip  is  wholly  free  from  nerve-cells. 

From  the  above  facts  certain  inferences  have  been  drawn : 
1.  It  has  been  concluded  that  the  sinus  is  the  originator  and 
director  of  the  movements  of  the  rest  of  the  heart.  2.  That  this 
is  owing  to  the  ganglia  in  its  walls.  While  all  recognize  the 
importance  of  the  sinus,  some  physiologists  hold  to  the  gangli- 
onic influence  as  essential  to  the  heart-beart,  still ;  while  others, 
influenced  by  the  facts  mentioned  above,  are  disposed  to  regard 
them  as  of  very  doubtful  importance — at  all  events,  as  origina- 
tors of  the  movements  of  the  heart. 

The  tendency  now  seems  to  be  to  attach  undue  imj^ortance 
to  the  spontaneous  contractility  of  the  heart-muscle ;  for  it  by 
no  means  follows  Logically  that,  because  a  muscle  treated  by 
electricity,  when  cut  off  from  the  usual  nerve  influence  that  we 
]>elieve  is  being  constantly  exerted  on  the  heart  like  other  or- 
gans, will  contract  and  continue  to  do  so  in  the  absence  of  the 
stimulus,  it  does  so  normally;  or,  because  some  hearts  beat  in 
the  absence  of  nerve-cells,  that  therefore  nerve-cells  are  of  no 
account  in  any  case.  Such  views,  when  pressed  to  the  extreme, 
lead  to  as  na?-rf)\v  conceptions  as  those  they  are  intended  to  re- 
place 

Taking  into  account  the  facts  mentioned  and  others  wo  have 


264  ANIMAL  PHYSIOLOGY. 

not  space  to  enumerate,  we  submit  the  following  as  a  safe  view 
to  entertain  of  the  beat  of  the  heart  in  the  light  of  our  present 
knowledge : 

Recent  investigations  show  clearly  that  there  are  great  dif- 
ferences in  the  hearts  of  animals  of  diverse  groups,  so  that  it 
is  not  possible  to  speak  of  "the  heart"  as  though  our  remarks 
applied  equally  to  this  organ  in  all  groups  of  animals. 

It  must  be  admitted  that  our  understanding  of  the  hearts  of 
the  cold-blood  animals  is  greater  than  of  the  mammalian  heart ; 
while,  so  far  as  exact  or  experimental  knowledge  is  concerned, 
the  human  heart  is  the  least  understood  of  all,  though  there  is 
evidence  of  a  pathological  and  clinical  kind  and  subjective 
experience  on  which  to  base  conclusions  possessing  a  certain 
value;  but  it  is  clear  to  those  who  have  devoted  attention  to 
(Comparative  physiology  that  the  more  this  subject  is  extended 
the  better  prepared  we  shall  be  for  taking  a  broad  and  sound 
view  of  the  physiology  of  the  human  heart  and  man's  other 
organs. 

Whatever  may  be  said  of  the  invertebrates,  among  which 
greater  simplicity  of  mechanism  doubtless  jjrevails,  there  can 
be  no  doubt  that  the  execution  of  a  cardiac  cycle  of  the  heart 
in  all  vertebrates,  and  especially  in  the  higher,  is  a  very  com- 
plex process  from  the  number  of  the  factors  involved,  their  in- 
teraction, and  their  normal  variation  with  circumstances ;  and 
we  must  therefore  be  suspicious  of  any  theory  of  excessive  sim- 
plicity in  this  as  well  as  other  parts  of  physiology. 

We  submit,  then,  the  following  as  a  safe  provisional  view  of 
the  causation  of  the  heart-beat : 

1.  The  factors  entering  into  the  causation  of  the  heart-beat 
of  all  vertebrates  as  yet  examined  are :  (a)  A  tendency  to  spon- 
taneous contraction  of  the  muscle-cells  composing  the  organ ; 
(5)  intra-cardiac  blood-pressure ;  (c)  condition  of  nutrition  as 
determined  directly  by  the  nervous  supply  of  the  organ  and  in- 
directly by  the  blood. 

2.  The  tendency  to  spontaneous  contraction  of  muscle-cells 
is  most  marked  in  the  oldest  parts  of  the  heart  (e.  g.,  sinus), 
ancestrally  (phylogenetically)  considered. 

3.  Intra-cardiac  pressure  exercises  an  influence  in  determin- 
ing the  origin  of  pulsation  in  probably  all  hearts,  though  like 
other  factors  its  influence  varies  with  the  animal  group.  In 
the  mollusk  (and  allied  forms)  and  in  the  fish  it  seems  to  be  the 
controlling  factor. 

4.  We  must  recognize  the  power  one  cell  has  to  excite  when 


THE  CIRCULATION   OF   THE    BLOOD.  265 

in  action  neighboring  heart-cells  to  contraction.  The  ability 
that  one  protoplasmic  cell-mass  has  to  initiate  in  others,  under 
certain  circumstances,  like  conditions  with  its  own,  is  worthy 
of  more  serious  consideration  in  health  and  disease  than  it  has 
yet  received. 

5.  The  influence  of  the  cardiac  nerves  becomes  more  pro- 
nounced as  we  ascend  the  animal  scale.  Their  share  in  the 
heart's  beat  will  be  considered  later. 

6.  Apparently  in  all  hearts  there  is  a  functional  connection 
leading  to  a  regular  sequence  of  beat  in  the  difit'erent  parts,  in 
which  the  sinus  or  its  representatives  (the  terminations  of  great 
veins  in  the  heart)  always  takes  the  initiative.  One  part  hav- 
ing contracted,  the  others  must  necessarily  follow ;  hence  the 
rapid  onset  of  the  ventricular  after  the  auricular  contraction  in 
tlie  mammal,  and  the  long  wave  of  contraction  that  seems  to 
pass  evenly  over  the  whole  organ  in  cold-blooded  animals. 

The  basis  of  all  these  factors  is  to  be  sought  finally  in  the 
natural  contractility  of  protoplasm.  A  heart  in  its  most  devel- 
oped form  still  retains,  so  to  speak,  the  inherited  but  modified 
Amoeba  in  its  every  cell. 

Whether  the  intrinsic  nerve -cells  of  the  heart  take  any 
share  directly  in  the  cardiac  beat  must  be  considered  as  yet 
undetermined.  Possibly  they  do  modify  motor  impulses  from 
nerves,  while  again  it  may  be  that  they  have  an  influence  over 
nutritive  processes  only.  The  subject  requires  further  study, 
both  anatomical  and  physiological. 

Influence  of  the  Vagus  Nerve  upon  the  Heart. 

The  principal  facts  in  this  connection  may  be  stated  as  fol- 
lows, and  apply  to  all  the  animals  thus  far  examined : 

L  In  all  cases  the  action  of  the  heart  is  modified  by  stimu- 
lation of  the  medulla  oblongata  or  the  vagus  nerve, 

2.  The  modification  may  consist  in  prompt  arrest  of  thfj 
heart,  in  slowing,  in  enfeeblement  of  the  beat,  or  a  combination 
of  the  two  latter  effects. 

3.  After  the  application  of  the  stimulation  there  is  a  latent 
period  before  the  effect  is  manifest,  and  the  latter  may  outlast 
the  stimulation  by  a  considerable  period. 

4.  In  most  animals  the  sinus  venosus  and  auricles  are  af- 
fected >>efore  the  ventricles,  and  the  vagus  may  influence  these 
parts  when  it  is  powerless  over  the  ventricle. 

5.  After  vagus  inhibition,  the  action  of  the  heart  is  (almost 


266 


ANIMAL   PHYSIOLOGY. 


unexceptionally)  different,  the  precise  result  being  variable,  but 
generally  the  beat  is  both  accelerated  and  increased  in  force. 


FiGf.  238.— Inhibition  of  frog's  heart  by  stimulation  of  the  vagus  nerve.  To  be  read  from  right 
to  left.  The  contractions  of  the  ventricle  are  registered  by  a  simple  lever  resting  on  it. 
The  interrupted  current  was  thrown  in  at  a.  Note  that  one  beat  occurred  before  arrest 
(latent  period),  and  that  when  standstill  of  the  heart  did  take  place  it  lasted  for  a  consider- 
able period  (Foster). 

We  may  say  that  the  working  capacity  of  the  heart  is  tem- 
porarily increased. 

6.  The  improvement  in  the  efficiency  of  the  heart  is  in  pro- 
portion to  its  previous  working  power,  and  in  cases  when  the 


stimulation  Vagufi. 


Fig.  239.— Effects  of  vagus  stimulation,  illustrated  by  a  form  of  sphygmographic  curve  derived 
•    from  the  carotid  of  a  rabbit  (Foster). 


action  is  feeble  and  irregular  (abnormal)  it  might  be  said  to  be 
in  proportion  to  its  needs.  This  is  a  very  important  law  that 
deserves  to  receive  a  general  recognition. 

7.  Section  of  both  vagi  nerves  results  in  histological  altera- 
tions in  the  heart's  structure,  chiefly  fatty  degeneration,  which 
must,  of  course,  impair  its  working  capacity  and  expose  it 
to  rupture  or  other  accidents  under  the  frequently  recurring 
strains  of  life. 


THE  CIRCULATION   OF   THE   BLOOD.  267 

8.  In  the  cold-blooded  animals  the  heart  may  be  kept  at  a 
standstill  by  vagus  stimulation  till  it  dies,  a  period  of  hours 
(one  case  of  six  hours  reported  for  the  sea-turtle). 

9.  Certain  drugs  (as  atropine),  applied  directly  to  the  heart, 
or  injected  into  the  blood,  prevent  the  usual  action  of  the 
vagus. 

10.  During  vagus  arrest  the  heart  substance  undergoes  a 
change,  resulting  in  an  unusual  dilatation  of  the  organ.  This 
may  be  witnessed  whether  the  heart  contains  blood  or  not. 

11.  The  heart  may  be  arrested  by  direct  stimulation,  espe- 
cially of  the  sinus,  and  at  the  points  at  which  the  electrodes  are 
applied  there  is  apparently  a  temporary  paralysis.  The  same 
alteration  in  the  beat  may  be  noticed,  as  when  the  main  trunk 
of  the  vagus  is  stimulated. 

12.  The  heart  may  be  inhibited  through  stimulation  of  vari- 
ous parts  of  the  body,  both  of  the  surface  and  internal  organs 
(reflex  inhibition), 

13.  One  vagus  being  divided,  stimulation  of  its  upper  end 
may  cause  arrest  of  the  heart. 

14.  Stimulation  of  a  small  part  of  the  medulla  oblongata 
will  produce  the  same  result,  provided  one  or  both  vagi  be 
intact. 

15.  Section  of  both  vagi  in  some  animals  (the  dog  notably) 
increases  the  rate  of  the  cardiac  beat.  The  result  of  section  of 
one  pneumogastric  nerve  is  variable.  The  heart's  rhythm  is 
usually  to  some  extent  quickened. 

16.  During  vagus  inhibition  from  any  cause  in  mammals 
and  many  other  animals,  the  heart  responds  to  a  single  stimu- 
lus, as  the  prick  of  a  needle,  by  at  least  one  beat.  An  observer 
studying  for  himself  the  behavior  of  the  heart  in  several  groups 
of  animals  with  an  open  mind,  for  the  purpose  of  observing 
all  he  can  rather  than  proving  or  disproving  some  one  point, 
becomes  strongly  impressed  with  the  variety  in  unity  that  runs 
through  cardiac  physiology,  including  the  influence  of  nerve- 
cells  (centers)  through  nerves;  for  it  will  not  be  forgotten  that 
normally  nerves  originate  nothing,  being  conductors  only,  so 
that  when  the  vagus  is  stimulated  by  us  we  are  at  the  most 
but  imitating  in  a  rough  way  the  work  of  central  nerve-cells. 
We  can  only  mention  a  few  points  to  illustrate  this. 

In  the  frog  a  succession  of  light  taps,  or  a  single  sharp  one 
("  Klopfversuch"  of  Ooltz),  will  usually  arnjst  tlie  heart  re- 
flexly;  though  sometimes  it  is  V(;ry  diflicult  to  acconii)lish. 
But  in  the  fisli  the  ease  with  which  tlio  heart  may  be  reflexly 


268 


ANIMAL   PHYSIOLOGY. 


inhibited  by  gentle  stimulation  of  almost  any  portion  of  the 
animal  is  wonderful.    Again,  in  some  animals  the  vagus  arrests 


R.  Vagus. 


Heart. 


Brain  above  Medulla. 


Cardio-inhibitory  Center 
in  Medulla  Oblongata. 


-Afferent  Nerve. 


Outlying  Area  with  its 

Nerves. 


Fig.  840.— Diagram  of  the  inhibitory  mechanism  of  the  heart.  The  arrows  indicate  in  all 
cases  the  path  the  nervous  impulses  take.  I.  Path  of  afferent  impulses  from  the  heart 
itself,  n.  Path  from  parts  of  the  brain  above  (or  anterior  to)  the  vaso-motor  center.  A 
similar  one  might,  of  course,  be  mapped  out  along  the  spinal  cord.  III.  Path  from  some 
peripheral  region.  The  downward  arrows  indicate  the  course  of  efferent  impulses,  which 
probably  usually  pass  by  both  vagi. 

the  heart  for  only  a  brief  period,  when  it  breaks  away  into  its 
usual  (but  increased)  action. 

In  the  fish,  menobranchus,  and  probably  other  animals,  the 
irritability  of  some  subdivision  of  the  heart  is  lost  during  the 
vagus  inhibition — i.  e.,  it  does  not  respond  to  a  mechanical 
stimulus. 

There  is  usually  a  certain  order  in  which  the  heart  recom- 
mences after  inhibition  (viz.,  sinus,  auricles,  ventricles) ;  but 
there  are  variations  in  this,  also,  for  different  animals.     It  is 


THE  CIRCULATION   OF   THE   BLOOD.  269 

also  a  fact  that  in  most  of  the  cold-blooded  animals  the  right 
vagus  is  more  efficient  than  the  left,  owing,  we  think,  not  to  the 
nerves  themselves  so  much  as  to  their  manner  of  distribution 
in  the  heart — the  greater  portion  of  the  driving  part  of  the 
organ,  so  to  speak,  being  supplied  by  the  right  nerve ;  for,  when 
even  a  small  part  of  the  heart  is  arrested,  it  may  be  overcome 
by  the  action  of  a  larger  portion  of  the  same,  or  a  more  domi- 
nant region  (the  sinus  mostly). 

Conclusions. — The  inferences  from  the  facts  stated  in  the 
above  paragraphs  are  these :  1.  There  is  in  the  medulla  a  col- 
lection of  cells  (center)  which  can  generate  impulses  that  reach 
the  heart  by  the  vagi  nerves  and  influence  its  muscular  tissue, 
though  whether  directly  or  through  the  intermediation  of 
nerve-cells  in  its  substance  is  uncertain.  It  may  possibly  be  in 
both  ways.  2.  This  center  (cardio-inhibitory)  may  be  influ- 
enced reflexly  by  influences  ascending  by  a  variety  x>f  nerves 
from  the  periphery,  including  paths  in  the  brain  itself,  as 
shown  by  the  influence  of  emotions  or  the  behavior  of  the 
heart.  3.  The  cardio-inhibitory  center  is  the  agent,  in  part, 
through  which  the  rhythm  of  the  heart  is  adapted  to  the  needs 
of  the  body.  4.  The  arrest,  on  direct  stimulation  of  the  heart, 
is  owing  to  the  effect  produced  on  the  terminal  fibers  of  the 
vagi,  as  shown  by  the  dilation,  etc.,  corresponding  to  what 
takes  place  when  the  trunk  of  the  nerve  or  the  center  is  stimu- 
lated. 5.  The  quickening  of  the  heart,  following  section  of  the 
vagi,  seems  to  show  that  in  some  animals  the  inhibitory  center 
exercises  a  constant  regulative  influence  over  the  rhythm  of 
the  heart,  6.  The  irritability  and  dilatability  of  the  cardiac 
tissue  may  be  greatly  modified  during  vagus  inhibition.  Some- 
times this  is  evident  before  the  rhythm  itself  is  appreciably 
altered.  7.  The  heart-muscle  has  a  latent  period,  like  other 
kinds  of  muscle ;  and  cardiac  effects,  when  initiated,  last  a 
variable  jjeriod. 

There  are  many  other  obvious  conclusions,  which  the  stu- 
dent will  draw  for  himself. 

But  a  question  arises  in  regard  to  the  significance  of  the 
f-ardiac  arrest  under  these  circumstances,  and  the  altered  action 
that  follows.  The  fact  that,  when  the  heart  is  severed  from  the 
central  nervous  system  by  section  of  its  nerves,  profound 
changes  in  the  minute  structure  of  its  cells  ensue,  points  un- 
mistakably to  some  nutritive  influence  that  must  have  operated 
through  the  vagi  nerves.  That  stimulation  of  the  vagus  re- 
stores regularity  of  rhythm  and  strengthens  the  beat  of  the 


270  ANIMAL   PHYSIOLOGY. 

failing  heart,  is  also  very  suggestive.  That  many  disorders  of 
the  heart  are  coincident  with  periods  of  mental  anguish  or 
worry,  and  that  in  certain  cases  of  severe  mental  application 
the  heart's  rhythm  has  become  very  slow,  also  point  to  influ- 
ences of  a  central  origin  as  greatly  affecting  the  life-processes 
of  this  organ. 

It  has  been  shown  that  the  vagus  nerve  in  some  cold-blooded 
animals,  as  is  probable  also  in  the  higher  vertebrates,  consists 
of  two  sets  of  fibers — those  which  are  inhibitory  jproi^er  and 
those  which  are  not,  but  belong  to  the  sympathetic  system. 

Separate  stimulation  of  the  former  favors  nutritive  pro- 
cesses, is  preservative;  of  the  latter,  destructive.  This  has 
been  expressed  by  saying  that  the  former  favors  constructive 
(anabolic)  metabolism ;  the  latter  destructive  (katabolic)  me- 
tabolism. It  is  assumed  that  all  the  metabolism  of  the  body 
may  be  represented  as  made  up  of  katabolic  following  anabolic 
processes. 

Whether  such  a  view  of  metabolism  expresses  any  more 
than  a  sort  of  general  tendency  of  the  chemistry  of  the  body 
is  doubtful.  It  is  a  very  simple  representation  of  what  in  all 
probability  is  extremely  complex ;  and  if  it  be  implied  that 
throughout  the  body  certain  steps  are  always  taken  upward  in 
construction  to  be  always  afterwards  followed  by  certain  down- 
ward destructive  changes,  we  must  reject  it  as  too  rigid  and 
artificial  a  representation  of  natural  processes. 

We  think,  however,  that,  upon  all  the  evidence,  pathological 
and  clinical  as  well  as  physiological,  the  student  may  believe 
that  the  vagus  nerve,  like  the  other  nerves  of  the  body,  accord- 
ing to  our  own  theory,  exercises  a  constant  beneficial,  guiding 
— let  us  say  determining — influence  over  the  metabolism  of  the 
organ  it  supplies ;  and  we  here  suggest  that,  if  this  view  were 
applied  to  the  origin  and  course  of  cardiac  disease,  it  would 
result  in  a  gain  to  the  science  and  art  of  medicine. 

The  Accelerator  (Augmentor)  Nerves  op  the  Heart. 

It  has  been  known  for  many  years  that  in  the  dog,  cat,  rab- 
bit, and  some  other  mammals,  there  were  nerves  proceeding 
from  certain  of  the  ganglia  of  the  sympathetic  chain  high  up, 
stimulation  of  which  led  to  an  acceleration  of  the  heart-beat. 
Very  recently  these  nerves  have  been  traced  in  a  number  of 
cold-blooded  animals,  and  the  whole  subject  placed  on  a  broader 
and  sounder  basis. 


THE   CIRCULATION   OF   THE   BLOOD. 


271 


There  are  variations  in  the  distribntion  of  these  nerves  for 
different  groups  of  animals,  but  it  will  suffice  if  we  indicate 
their  course  in  a  general  way,  without  special  reference  to  the 
variations  for  each  animal  group :  1.  These  nerves  emerge  from 
the  spinal  cord  (upper  dorsal  region),  and  proceed  upward 
before  being  distributed  to  the  heart,  2.  They  may  leave  for 
their  cardiac  destination  either  at  (a)  the  first  thoracic  (or  basal 
cardiac  ganglion,  as  it  might  be  named  in  this  case),  (b)  the  in- 
ferior cervical  ganglion,  (c)  the  annulus  of  Vieussens,  or  {d)  the 
middle  cervical  ganglion. 


2  n Middle  Cervical  Ganglion. 


Spinal  Cord. 


Accelerator  Center  in  Medulla. 


Superior  Cervical  Ganglion. 


3  Q- 1 —     Inferior  Cervical  Ganglion. 


Region  of  First  Rib. 


Accelerator  Nerves. 


Heart. 


Fio.  211.— Diagram  to  illustrate  the  origin,  course,  etc.,  of  accelerator  impulses.  It  will  be 
understood  that  this  is  inU'tided  to  iiidi<;ate  the  general  plan,  and  not  preciselv  what  takes 
pla<'e  in  any  one  atiiinal.  Thus,  while  the  accel<Tatf)r  nerves  ina.v  arise  in  tnis  way,  it  is 
not  meant  to  be  iinpNed  that  IIk-  heart  is  actually  supplied  by  ihrcr  nei'ves  of  such  origin 
in  any  cas*-.     The  arrows,  as  l)efor<'.  indicate  the  path  of  the  impulses. 


Their  course  has  been  traced  by  lihysiological  iindhods;  thus 
it  has  been  foiiiid  that,  in  all  animals  examined,  stimulation 
of  the  spinal  cf>rd  or  tlu;  various  parts  mentioned  al)()ve,  or 
nerve  brandies  from  tliem,  gave  rise  either  to  ac^celcsration  of 


272  ANIMAL   PHYSIOLOGY. 

the  cardiac  beat  or  augmentation  of  its  force^  or  to  both,  as  is 
commonly  the  case.  In  every  instance  the  work  of  the  heart 
is  increased,  so  that  they  may  be  called  more  appropriately 
augmentor  nerves;  and  their  effect  may  be  more  evident  on 
one  part  of  the  heart,  as  regards  increase  of  the  force  of  the 
beat,  than  on  another. 

They  require  for  their  fullest  effect  a  rather  strong  and  con- 
tinuous stimulation  (interrupted  current),  and  the  augmenta- 
tion outlasts  the  stimulus  a  considerable  period.  The  same  law 
applies  to  them  as  to  the  vagus  nerve,  viz.,  that  the  result  is 
inversely  proportional  to  the  rhythm  of  the  heart  at  the  period 
of  stimulation ;  a  slow-beating  heart  will  be  more  augmented 
proportionally  than  a  rapidly-pulsating  organ. 

It  is  noticeable  that  after  one  or  more  experiments  the  heart 
often  falls  into  an  irregular  or  weakened  action  quite  the  re- 
verse of  what  ensues  when  the  vagus  is  stimulated.  But  it  has 
also  been  observed  that  certain  of  the  vagus  fibers  on  stimula- 
tion give  rise  to  a  like  result. 

Further,  it  is  found  that  the  electrical  condition  of  the  heart 
is  different,  according  as  the  inhibitory  or  other  fibers  of  the 
heart  are  stimulated.  The  latter  fact  seemed  to  point  strongly 
to  a  fundamental  difference  in  their  effect  on  cardiac  metabo- 
lism ;  hence  it  is  proposed  to  speak  of  the  vagus  as  a  vago- 
sympathetic nerve,  containing  inhibitory  fibers  proper  and 
sympathetic  or  motor  fibers  to  be  classed  with  the  nerves  that 
were  formerly  known  as  "  accelerators,"  and  to  be  compared 
in  their  action  to  the  ordinary  motor  nerves  of  voluntary 
muscles. 

Indeed,  these  conceptions  will  probably  give  rise  to  a  broader 
view  of  the  whole  nervous  system,  especially  as  regards  the 
relations  of  the  nerves  themselves. 

Certainly  the  augmentor  nerves  to  which  we  are  now  refer- 
ring exhaust  the  heart,  lead  it  to  expend  its  nutritive  capital, 
and  leave  it  worse  than  before.  One  can  understand  the  ad- 
vantage in  the  heart  having  a  double  supply  of  nerve-fibers 
with  opposite  action ;  and  it  is  worthy  of  special  note  in  this 
connection  that,  when  the  vagus  (vago-sympathetic)  is  stimu- 
lated at  the  same  time  as  the  augmentors,  the  inhibitory  effect, 
preservative  of  nutritive  resources,  prevails. 

It  will  be  seen  that  the  heart  may  be  made  to  do  increased 
work  in  three  ways :  Firstly,  the  relaxation  of  a  normal  inhibi- 
tory control  through  the  vagus  nerve  by  the  cardio-inhibitory 
center;  secondly,  through  the  sympathetic  (motor)  fibers  in 


THE  CIRCULATION   OF   THE   BLOOD.  273 

the  vagus  itself ;  and,  finally,  through  fibers  with  similar  action 
in  the  sympathetic  system,  usually  so  called. 

The  share  taken  by  these  factors  is  certainly  variable  in  dif- 
ferent species  of  animals,  and  it  is  likely  that  this  is  true  of  the 
same  animals  on  difl^erent  occasions.  It  is  also  conceivable, 
and  indeed  probable,  that  they  act  together  at  times,  the  inhibi- 
tory action  being  diminished  and  the  augmentor  influence  in- 
creased. 

Human  Physiology. — Of  the  three  cardiac  nerves — superior, 
middle,  and  inferior — the  strongest,  which  is  the  middle  one, 
passes  from  the  inferior  cervical  ganglion  to  the  middle,  from 
which  it  proceeds  to  the  heart,  and  the  inferior,  may  be  re- 
garded as  the  chief  augmentor  cardiac  nerves. 

That  man's  pneumogastric  contains  inhibitory  fibers  is  evi- 
dent from  the  experiment  of  Czermak,  who,  by  pressing  a  bony 
tumor  in  his  neck  against  his  vagus  nerve,  could  arrest  his 
heart.  Another  individual  could  arrest  his  heart-beat  at  will, 
and  if  not  through  the  vagus,  how  ? 

We  are  probably  all  aware  of  alterations  in  the  rhythm  of 
the  heart  from  emotions.  During  a  period  of  intense,  brief, 
sympathetic  anxiety,  as  in  watching  two  competitors  during  a 
severe  struggle  for  supremacy,  a  change  in  the  rhythm  of  the 
heart,  amounting,  it  may  be,  to  momentary  arrest,  may  be 
observed. 

Enough  has  been  said,  we  trust,  to  show  that  the  nerves  of 
the  heart  can  no  longer  be  regarded  merely  as  the  reins  for 
bridling  the  cardiac  steed;  but  that  all  the  phenomena  of  accel- 
eration, slowing,  or  other  changes  of  rhythm,  are  only  the  out- 
ward evidences  of  profound  vital  changes  accompanied  by  cor- 
responding chemical  and  electrical  effects.  If  tliese  views  be 
correct,  nervous  influence  must  play  no  small  part  in  the  causa- 
tion and  modification  of  disordered  conditions ;  and  we  would 
extend  such  a  view  to  all  the  organs  of  the  body,  and  especially 
in  the  case  of  man.  The  heart's  rhythm  can,  however,  be 
modified  in  other  ways  than  we  have  as  yet  described. 

Th(;ugh  an  isolated  heart,  fed  by  serum  or  some  artificial 
nutritive  fluid,  may  beat  well  for  a  time,  it  is  liable  to  peri- 
odic interruptions,  which  are  probably  owing  to  its  imperfect 
nutrition. 

Many  drugs  greatly  modify  the  heart-beat;  but,  in  attempt- 
ing to  exjjlain  how  the  result  is  accomplished,  the  difficulty  is 
in  UMi-av<'ling  tluj  i)art  each  anatomical  element  plays  in  the 
total   result.     Does  the  drug  act  on  the  muscular  tissue,  the 

18 


2T4  ANIiVlAL   PHYSIOLOGY. 

nerve  terminals,  or  the  ganglia;   or  does  it  affect  the  heart 
through  the  central  nervous  system  ? 

Resort  to  comparative  physiology  is  important  in  such  cases, 
if  only  to  foster  caution  and  avoid  narrow  views. 

The  Heart  in  Relation  to  Blood- Pressure. 

It  is  plain  that  all  the  other  conditions  throughout  the  cir- 
culatory system  remaining  the  same,  an  increase  in  either  the 
force  or  the  frequency  of  the  heart-beat  must  raise  the  blood-press- 
ure. But,  if  the  pressure  were  generally  raised  when  the  heart 
beats  rapidly,  it  would  fare  ill  with  the  aged,  the  elasticity  of 
their  arteries  being  usually  greatly  impaired.  As  a  matter  of 
fact  any  marked  rise  of  pressure  that  would  thus  occur  is  pre- 
vented as  a  rule,  and  in  different  ways,  as  will  be  seen ;  but,  so 
far  as  the  heart  is  concerned,  its  beat  is  usually  the  weaker  the 
more  rapid  it  is,  so  that  the  cardiac  rhythm  and  the  blood- 
pressure  are  in  inverse  proportion  to  each  other. 

By  what  method  is  the  heart's  action  tempered  to  the  condi- 
tions prevailing  at  the  time  in  the  other  parts  of  the  vascular 
system  ? 

The  matter  is  complex.  It  is  possible  to  conceive  that  there 
is  a  local  nervous  apparatus  which  regulates  the  beat  of  the 
heart  according  to  the  intra-cardiac  pressure,  which  latter  again 
will  depend  on  conditions  outside  of  the  heart  itself — the  arte- 
rial pressure,  in  fact.  It  is  possible  to  understand  that,  apart 
from  any  nervous  elements  at  all,  the  cardiac  cells  regulate 
their  own  action  in  obedience  to  the  impressions  made  upon 
them. 

But,  inasmuch  as  the  heart  is  not  regulated  perfectly  in  the 
mammal  according  to  the  blood -pressure,  when  the  vagi  nerves 
are  cut,  and  considering  the  dominance  of  the  central  nervous 
system,  it  does  not  seem  likely  that  it  should  resign  the  con- 
trol of  so  important  a  matter.  Experiment  bears  this  out. 
There  is  some  evidence  for  believing  that  not  only  may  the 
vagus  itself  act  as  an  afferent  sensory  nerve,  but  that  the  de- 
pressor nerve,  to  be  shortly  referred  to  more  particularly,  is 
also  such  a  sensory  nerve. 

However,  such  a  view  does  not  exclude  previously  men- 
tioned factors,  and  there  can  be  little  doubt  that  in  forms  below 
mammals  the  muscular  tissue  is  to  some  degree  self -regulative ; 
and  it  is  not  likely  that  this  quality  is  wholly  lost  even  in  the 
highest  mammals. 


THE   CIRCULATION  OP  THE   BLOOD. 


275 


V^y 


The  effect  of  vagus  stimulation  on  the  blood-pressure  is 
always  very  marked,  as  would  be  supposed.  To  examine  an 
extreme  case,  suppose  the  heart  arrested  for  a  few  seconds,  the 
elastic  recoil  of  the  arteries  continues  to  maintain  for  a  time 
the  blood-pressure,  though  there  is,  of  course,  an  immediate 
and  pronounced  fall.  And  it  may  be  remarked,  by-the-way, 
that  in  cases  of  fainting,  when  the  heart  ceases  to  beat,  or  beats 
in  the  feeblest  man- 
ner, the  importance 
of  this  arterial  elas- 
ticity as  a  force, 
maintaining  the 
circulation  for  sev- 
eral seconds  at 
least,  is  of  great 
importance. 

As  seen  in  the 
tracing,  the  beats, 
when      the     heart 

commences    its    aC-     Fig.  242. —Tracing  from  a  rabbit,  showing  the  influence  of  car- 
diac inhibition  on  blood-pressure.     The  fall  in  this  case 
tion    ao"ain     tell    on  ^^^  very  rapid,  owing  to  sudden  cessation  of  the  heart- 

^         '         .  beat.    The  relative  emptiness  of  the  vessels  accounts  for 

the      comparatively  the  pecuUar  character  of  the  curve  of  rising  blood-pressure 

slack'  walls  of  the 

arteries,  distending  them  greatly,  and  this  may  be  made  evident 
by  the  sphygmograph  as  well  as  the  manometer ;  indeed,  may 
be  evident  to  the  finger,  the  pulse  resembling  in  some  features 
that  following  excessive  loss  of  blood. 

If  the  heart  has  been  merely  slowed,  or  its  pulsation  weak- 
ened, the  effects  will  of  course  be  less  marked. 

The  Quantity  of  Blood. — The  blood-pressure  may  also  be 
augmented,  the  cardiac  frequency  remaining  the  same,  by 
the  quantity  of  blood  ejected  from  the  ventricles,  which  again 
depends  on  the  quantity  entering  them,  a  factor  determined 
by  the  condition  of  the  ves.sels,  and  to  this  we  shall  presently 
turn. 

In  consequence  of  changes  in  different  X)arts  of  the  system 
by  way  of  compensation,  results  follow  in  an  animal  which 
might  not  have  been  anticipated. 

Thus,  ble(;ding,  unless  to  a  dangerous  extreme,  does  not 
lower  the  blood -pressure  except  temy)orarily.  It  is  estimated 
that  the  body  can  adapt  itself  to  a  loss  of  as  much  as  3  per 
cent  of  the  body-weight. 

The  adaptation  is  probably  not  through  absorption  chiefly, 


276  ANIMAL   PHYSIOLOGY. 

but  through,  constriction  of  the  vessels  by  the  vaso-motor 
nerves. 

Again,  an  injection  of  fluid  into  the  blood  does  not  cause  an 
appreciable  rise  of  blood-pressure,  so  long  as  the  nervous  sys- 
tem is  intact ;  but,  if  by  section  of  the  spinal  cord  the  vaso- 
motor influences  are  cut  off,  then  a  rise  may  take  place  to  the 
extent  of  2  to  3  per  cent  of  the  body-weight,  the  extra  quan- 
tity of  fluid  seeming  to  be  accommodated  in  the  capillaries  and 
smaller  veins.  These  facts  are  highly  significant  in  illustrat- 
ing the  adaptive  power  of  the  circulatory  system  (protective  in 
its  nature),  and  are  of  practical  importance  in  the  treatment  of 
disease. 

We  think  the  benefit  that  sometimes  follows  bleeding  has 
not  as  yet  received  an  adequate  explanation,  but  we  shall  not 
attempt  to  tackle  the  problem  now.  Changes  in  the  circulation 
depend  on  variations  in  the  size  of  the  blood-vessels. 

It  is  important  in  considering  this  subject  to  have  clear  no- 
tions of  the  structure  of  the  blood-vessels.  It  will  be  borne  in 
mind  that,  while  muscular  elements  are  perhaps  not  wholly 
lacking  in  any  of  the  arteries,  they  are  most  abundant  in  the 
smallest,  the  arterioles,  which  by  their  variations  in  size  are 
best  fitted  to  determine  the  quantity  of  blood  reaching  any 
organ.  It  is  well  known  that  nerves  derived  chiefly  from  the 
sympathetic  system  pass  to  blood-vessels,  though  their  exact 
mode  of  termination  is  obscure. 

We  may  now  examine  into  the  nature  of  certain  facts,  which 
may  be  stated  briefly  thus : 

1.  In  certain  vascular  areas  of  some  vertebrates,  as  in  the 
vessels  of  the  ear  of  the  rabbit  and  this  animal's  saphena 
artery,  rhythmical  variations  in  the  size  of  the  small  arteries 
may  be  observed ;  also  in  the  veins  of  the  bat's  wing  and  of  the 
fins  of  certain  fishes  (e.  g.,  caudal  vein  of  the  eel),  as  well  as  in 
certain  arteries  of  some  groups  of  the  cold-blooded  animals. 

2.  Under  the  microscope  the  arterioles  of  various  parts  of 
the  frog,  including  those  of  the  muscles,  may  be  seen  to  vary 
apparently  spontaneously,  and  may  through  stimulation  be 
made  to  depart  widely  from  their  usual  size. 

3.  Section  of  a  large  number  of  nerves  is  followed  by  red- 
dening of  the  parts  to  which  they  are  distributed.  This  is  well 
seen  when  the  cervical  sympathetic  of  the  rabbit  is  divided ;  the 
ear  becomes  redder,  owing  to  obvious  dilatation  of  its  blood- 
vessels ;  and  warmer,  owing  to  the  increased  quantity  of  blood 
in  it,  etc.     It  has  also  been  noticed  in  cases  of  paralysis,  and 


THE  CIRCULATION  OF  THE   BLOOD.  277 

especially  in  gunshot  and  other  wounds  involving  nerves,  that 
vaso-motor  effects  have  followed. 

4.  Section  of  certain  nerves,  as  the  nervi  erigentes  of  the 
penis,  is  not  followed  by  dilatation ;  but  these  nerves  and  the 
chorda  tympani  supplying  the  salivary  gland  are  examples  of 
so-called  vaso-dilators,  inasmuch  as  their  stimulation  gives  rise 
to  enlargement  of  the  caliber  of  the  arterioles  in  their  area  of 
distribution. 

5.  On  the  other  hand,  such  a  nerve  as  the  cervical  sympa- 
thetic, as  may  be  readily  shown  in  the  rabbit,  when  its  periph- 
eral end  is  stimulated,  gives  rise  to  constriction,  and  hence  is 
termed  a  vaso-consiricior. 

6.  When,  however,  the  divided  sciatic  nerve  is  stimulated 
peripherally,  the  result  may  be  either  constriction  or  dilata- 
tion. 

7.  When  the  spinal  cord  of  an  animal  is  divided  across, 
there  is  vascular  dilatation  of  all  the  parts  below  the  section 
(loss  of  arterial  tone) ;  but  in  time  the  vessels  return  to  their 
usual  size  (restoration  of  arterial  tone). 

8.  On  destruction  of  a  certain  minute  portion  of  the  medulla 
oblongata,  there  is  a  general  loss  of  arterial  tone.  This  area 
(center)  extends  in  the  rabbit  from  a  short  distance  below  the 
corpora  quadrigemina  (1  to  2  mm.)  to  within  4  to  5  of  the 
calamus  scriptorius,  as  ascertained  by  the  effects  on  the  vessels 
of  cutting  away  the  medulla  in  thin  transverse  sections.  At 
the  spot  indicated  there  is  a  collection  of  large  multipolar 
nerve-cells  (antero-lateral  nucleus  of  Clarke). 

Conclusions. — 1.  There  are  vaso-motor  nerves  of  two  kinds — 
vaso-constrictors  and  vaso-dilators — which  may  exist  in  nerve- 
trunks  either  alone  or  mingled. 

Examples  of  the  former  are  found  in  the  cervical  sympa- 
thetic, splanchnic,  etc.,  of  the  latter  in  the  chorda  tympani, 
nerves  of  the  muscles  and  nervi  erigentes  (from  the  first,  second, 
and  third  sacral  nerves),  while  the  sciatic  seems  to  contain 
both.  2.  Impulses  are  constantly  passing  from  the  medullary 
vaso-motor  center  along  the  nerves  to  the  blood-vessels,  hence 
their  dilatation  after  section  of  the  nerves. 

The  nerves  are  traceable  to  the  spinal  cord,  and  in  some 
part  of  their  course  run,  as  a  rule,  in  the  sympathetic  system. 
'.i.  Impulses  j>ass  at  intervals  to  the  areas  of  (listri})utif)n  of 
vaso-dilators  along  these  nerves,  the  effect  of  which  is  to  dilate 
the  vessels  through  their  influence,  as  in  other  cases,  on  the 
muscular  coat. 


278 


ANIMAL  PHYSIOLOGY. 


It  is  stated  that  in  course  of  time  the  vessels  of  the  rabbit's 
ear  regain  their  tone,  notwithstanding  that  the  influence  of  the 


Spinal  Cord 


Vaso-motor  Center  in 

\/'^\    /  Medulla. 


Depressor  Nerve. 


Efferent  Vaso-raotor 
Nerve. 


Outlying  Vascular 
Area. 


Afferent  Nerve  from 
Periphery. 


Fig.  243. — Diagram  of  nervous  vasomotor  mechanism.  I.  Course  of  afferent  impulses  from 
the  heart  itself  along  the  depressor  nerve.  II.  Course  from  some  other  part  of  the  brain. 
ni.  Course  from  some  peripheral  region  along  a  nerve  joining  the  spinal  cord.  The  effer- 
ent impulses  are  represented  as  passing  to  a  vascular  area,  reduced  for  the  sake  of  sim- 
plicity to  a  single  arteriole. 

central  nervous  system  has  been  cut  off  by  section  of  the  vaso- 
motor nerves. 

To  explain  this  result,  a  local  nervous  mechanism  has  been 
assumed  to  exist,  though  not  demonstrated  either  anatomically 
or  physiologically.  Interesting  experiments  have  lately  shown 
that  both  in  mammals  and  cold-blooded  animals  the  effect  on 
the  blood-vessels  varies  with  the  intensity  and  character  of  the 
stimulus,  and  not  only  with  the  group  of  animals  tested,  but 
even  with  the  same  individuals  at  different  periods  during  the 
experiment ;  and  we  take  the  opportunity  to  renew  our  expres- 
sion of  opinion  with  this  fresh  evidence  that  the  laws  of  physi- 
ology can  not  be  laid  down  in  the  rigid  way  that  has  prevailed 


THE  CIRCULATION  OF  THE  BLOOD.  279 

to  so  large  an  extent  up  to  the  present  time ;  but  that  our  widen- 
ing experience  shows  (what  ought  to  have  been  expected)  that 
the  greatest  allowance  mast  be  made  for  group  if  not  individ- 
ual variations  everywhere.  There  is  also  evidence  to  show  that 
the  mode  of  stimulation  in  experimental  cases  causes  the  result 
to  vary.  From  such  facts  as  are  stated  in  paragraph  seven,  it 
is  inferred  that  there  are  vaso-motor  centers  in  the  si3inal  cord 
which  are  usually  subordinated  to  the  main  center  in  the  me- 
dulla, but  which  in  the  absence  of  the  control  of  the  chief  cen- 
ter in  the  medulla  assume  an  independent  regulating  influence. 

A  local  vaso-motor  mechanism  does  not  seem  to  us  neces- 
sary to  explain  the  changes  which  the  blood-vessels  undergo, 
and  should  not  be  adopted  as  an  article  of  physiological  faith 
till  demonstrated  to  exist.  If  we  assume  that  the  independent 
contractility  of  muscle-cells  is  retained  in  the  blood-vessels, 
and  that,  when  freed  from  the  influence  of  the  central  nervous 
system,  which  becomes  more  and  more  dominant  as  we  ascend 
the  animal  scale,  there  is  a  reversion  to  an  ancestral  condition, 
a  new  light  is  thrown  upon  the  facts.  It  is  a  case  of  old  habits 
gaining  sway  when  the  check-rein  of  nervous  influence  is  re- 
moved ;  and,  as  we  shall  show  from  time  to  time,  this  law  applies 
to  every  organ  of  the  body.  Moreover,  not  to  go  beyond  the 
vascular  system,  this  independent  rhythmic  activity  is  seen  in 
the  isolated  sections  of  the  pulsatile  veins  of  the  bat's  wing, 
devoid,  so  far  as  we  know,  of  nervous  cells.  Such  facts  lend 
some  color  to  the  view  that,  after  distention  of  the  vessels  by 
the  cardiac  systole,  the  return  to  their  previous  size  is  aided  by 
rhythmical  contractions  of  the  muscle-cells. 

Let  us  now  consider  certain  other  well-known  experimental 
facts : 

1.  There  is  a  nerve  with  variable  origin,  course,  etc.,  in  dif- 
ferent mammals,  but  in  the  rabbit  given  off  from  either  the 
vagus,  the  superior  laryngeal,  or  by  a  branch  from  each, 
which,  running  near  the  sympathetic  nerve  and  the  carotid 
artery,  reaches  the  heart,  to  which  it  is  distributed.  This  is 
known  as  the  deprefisor  nerve. 

2.  The  vagi  nerves  having  been  divided,  stimulation  of  the 
central  end  of  the  cut  depressor  nerve  is  followed  by  a  fall  in 
blood-prf!ssure,  which  may  not  be  accompanied  by  any  altera- 
tion in  the  cardiac  rliythm. 

3.  This  effect  may  in  great  part  be  prevented  if  the  splancli- 
nic  nerves  be  divided  previous  to  stimulation  of  the  depressor. 

4.  If  the  splanchnic  area  (region  of  the  main  abdominal 


280 


ANIMAL  PHYSIOLOGY. 


viscera)  be  inspected  during  the  fall  in  blood-pressure,  it  may- 
be noticed  that  there  is  vascular  fullness  under  these  circum- 
stances. 

These  results  are  interpreted  as  being  due  to  afferent  im- 
pulses ascending  the  depressor,  acting  on  the  vaso-motor  center^ 


Fig.  244. — Curve  of  blood-pressure  resulting  from  stimulation  of  the  central  end  of  the  de- 
pressor nerve.  To  be  read  from  right  to  left.  T  indicates  the  rate  at  which  the  recording 
surface  moved,  the  intervals  denoting  seconds.  At  C  the  current  was  thrown  into  the 
nerve,  and  shut  off  at  O.  The  result  appears  after  a  period  of  latency,  and  outlasts  the 
stimulus  (Foster). 

and  interfering  with  (inhibiting)  the  outflow  of  efferent,  con- 
strictive, or  tonic  impulses,  which  start  from  the  vaso-motor 
center,  descend  the  cord,  and  find  their  way  to  the  organs  of 
the  region  in  question,  in  consequence  of  which  the  mus- 
cular coats  of  the  arterioles  relax,  more  blood  flows  to  this 
area  which  is  very  large,  and  the  general  blood-pressure  is 
lowered. 

Again,  if  the  central  end  of  one  of  the  main  nerves — e.  g., 
sciatic — be  stimulated,  a  marked  change  in  the  blood-pressure 
results,  but  whether  in  the  direction  of  rise  or  fall  seems  to 
depend  upon  the  condition  of  the  central  nervous  system,  for, 
with  the  animal  under  the  influence  of  chloral,  there  is  a  fall ; 
if  under  urari,  a  rise. 

It  is  not  to  be  supposed  that  the  change  in  any  of  these 
cases  is  confined  to  any  one  vascular  area  invariably,  but  that 
it  is  this  or  that,  according  to  the  nerve  stimulated,  the  condi- 
tion of  the  centers,  and  a  number  of  other  circumstances. 
Moreover,  it  is  important  to  bear  in  mind  that  with  a  fall  of 
blood-pressure  in  one  region  there  may  be  a  corresponding  rise 
in  another.  With  these  considerations  in  mind,  it  will  be  ap- 
parent that  the  changes  in  the  vascular  system  during  the 


THE  CIRCULATION   OF   THE  BLOOD.  281 

course  of  a  single  hour  are  of  the  most  complex  and  variable 
character. 

Though  special  attention  has  been  drawn  to  such  rhyth- 
mical variations  as  may  be  witnessed  in  the  rabbit's  ear,  bat's 
wing,  etc.,  there  can  be  little  doubt  that  changes  as  marked, 
though  possibly  less  distinctly  rhythmical,  are  constantly  tak- 
ing place  in  the  vertebrate  body,  and  especially  in  that  of  man, 
with  his  complex  emotional  nature  and  the  many  vicissitudes 
of  modern  civilized  life.  The  frequent  changes  in  color  in  the 
faces  of  certain  people  are  in  this  connection  suggestive,  though 
we  hope  we  have  made  it  clear  that  these  vascular  modifica- 
tions are  dependent  chiefly  on  centripetal  influences  from  every 
quarter,  though  actually  brought  about  by  centrifugal  im- 
pulses. Whether  there  is  a  rhythm  obscured  by  minor  rhythms, 
owing  to  an  independent  or  automatic  action  of  the  vaso-motor 
center,  though  not  improbable,  must  be  regarded  as  undeter- 
mined as  yet. 

The  question  of  the  distribution  of  vaso-motor  nerves  to 
veins  is  also  one  to  which  a  definite  answer  can  not  be  given. 

The  Capillaries. 

The  cells  of  which  the  capillaries  are  composed  have  a  con- 
tractility of  their  own,  and  hence  the  caliber  of  the  capillaries 
is  not  determined  merely  by  the  arterial  pressure  or  any  similar 
mechanical  effect. 

Certain  abnormal  conditions,  induced  in  these  vessels  by 
the  application  of  irritants,  cause  changes  in  the  blood-flow, 
which  can  not  be  explained  apart  from  the  vitality  of  the  ves- 
sels themselves. 

Watched  through  the  microscope  under  such  circumstances, 
the  blood-corpuscles  no  longer  pursue  their  usual  course  in  the 
mid-stream,  but  seem  to  be  generally  distributed  and  to  hug  the 
walls,  one  result  of  which  is  a  slowing  of  the  stream,  wholly 
independent  of  events  taking  place  in  other  vessels.  It  is  thus 
seen  that  in  this  Ci^ndition  {stasis)  the  capillaries  have  an  in- 
dependent influence  essentially  vital.  We  say  independent,  for 
it  is  still  an  open  question  whether  nerves  are  distributed  to 
capillaries  or  not.  That  inflammation,  in  which  also  the  walls 
undergo  such  serious  changes  that  white  and  even  red  l)lood- 
cells  may  pass  through  thom  {diapedesis),  is  not  uninfluenced 
by  the  nervous  system,  possiljly  induced  through  it  in  certain 
cases,  if  not  all,  seems  more  than  i)iobjible. 


282  ANIMAL  PHYSIOLOGY. 

But  when  we  consider  the  lymphatic  system  new  light  will, 
it  is  hoped,  be  thrown  upon  the  subject  of  the  nature  and  the 
influences  which  modify  the  capillaries.  One  thing  will  be 
clear  from  what  has  been  said,  that  even  normally  the  capil- 
laries must  exert  an  influence  of  the  nature  of  a  resistance, 
owing  to  their  peculiar  vital  properties ;  and,  as  we  have 
already  intimated,  such  considerations  should  not  be  excluded 
from  any  conclusions  we  may  draw  in  regard  to  tubes  that  are 
made  up  of  living  cells,  whether  arteries,  veins,  or  capillaries, 
though  manifestly  the  applicability  to  capillaries  with  their 
less  modified  or  more  primitive  structure  is  stronger. 

It  has  now  become  clear  that  the  circulation  may  be  modi- 
fied either  centrally  or  peripherally ;  that  a  change  is  never 
purely  local,  but  is  correlated  with  other  changes ;  that  the 
whole  is,  in  the  higher  animals,  directly  under  the  dominion 
of  the  central  nervous  system ;  and  that  it  is  through  this 
part  chiefly  that  harmony  in  the  vascular  as  in  other  sys- 
tems and  with  other  systems  is  established.  To  have  ade- 
quately grasped  this  conception  is  worth  more  than  a  knowl- 
edge of  all  the  details. 

Special  Considerations. 

Pathological. — Changes  may  take  place  either  in  the  sub- 
stance of  the  cardiac  muscles,  in  the  valves,  or  in  the  blood-ves- 
sels, of  a  nature  unfavorable  to  the  welfare  of  the  body.  Some 
of  these  have  been  incidentally  referred  to  already. 

Hypertrophy,  or  an  increase  in  the  tissue  of  the  heart,  is 
generally  dependent  on  increased  resistance,  either  within  or 
without  the  heart,  in  the  region  of  the  arterioles  or  capillaries. 
Imperfections  of  the  aortic  valves  may  permit  of  regurgitation 
of  blood,  entailing  an  extra  effort  if  it  is  to  be  expelled  in  addi- 
tion to  the  usual  quantity,  which  again  leads  to  hypertrophy ; 
but  this  is  often  succeeded  by  dilatation  of  the  chambers  of  the 
heart  one  after  the  other,  and  a  host  of  evils  growing  out  of 
this,  largely  dependent  on  imperfect  venous  circulation,  and 
increased  venous  pressure.  And  it  may  be  here  noticed  that 
arterial  and  venous  pressures  are,  as  a  general  rule,  in  inverse 
proportion  to  each  other. 

If  the  quantity  of  blood  in  the  ventricle,  in  consequence 
of  regurgitation,  should  prove  to  be  greater  than  it  can  lift 
(eject),  the  heart  ceases  to  beat  in  diastole ;  hence  some  of  the 
sudden  deaths  from  disease  of  the  aortic  valves. 


THE  CIRCULATION  OP   THE   BLOOD.  283 

As  a  result  of  fatty,  or  other  forms  of  degeneration,  the 
heart  may  suddenly  rupture  under  strains. 

Actual  experiment  on  the  arteries  of  animals  recently  dead, 
including  men,  shows  that  the  elasticity  of  the  arteries  of  even 
adult  mammals  is  as  perfect  as  that  of  the  vessels  of  the  child, 
so  that  man  ranks  lower  than  other  animals  in  this  respect. 

After  middle  life  the  loss  of  arterial  elasticity  is  consider- 
able and  progressive.  The  arteries  may  undergo  a  degenera- 
tion from  fatty  changes  or  deposit  of  lime ;  such  vessels  are,  of 
course,  liable  to  rupture ;  hence  one  of  the  frequent  modes  of 
death  among  old  persons  is  from  paralysis  traceable  to  rupture 
of  vessels  in  the  brain. 

These  and  other  changes  also  cause  the  heart  more  work, 
and  may  lead  to  hypertrophy.  Even  in  young  persons  the 
strain  of  a  prolonged  athletic  career  may  entail  hypertrophy 
or  some  other  form  of  heart-disease. 

We  mention  such  facts  as  these  to  show  the  more  clearly 
how  important  is  balance  and  the  power  of  ready  adaptation 
in  all  parts  of  the  circulation  to  the  maintenance  of  a  healthy 
condition  of  body. 

The  heart  is  itself  nourished  through  the  coronary  arteries ; 
so  that  morbid  alterations  in  these  vessels  cause,  if  not  sudden 
and  painful  death,  at  least  nutritive  changes  in  the  heart-sub- 
stance, which  may  lead  to  a  dramatic  end  or  to  a  slow  impair- 
ment of  cardiac  power,  etc. 

Personal  Observation. — The  circulation  is  one  of  those  depart- 
ments of  physiology  in  which  the  student  may  verify  much  upon 
his  own  person.  The  cardiac  impulse,  the  heart's  sounds  (with  a 
double  stethoscope),  the  pulse — its  nature  and  changes  with  cir- 
cumstances, the  venous  circulation,  and  many  other  subjects, 
are  all  easy  of  observation,  and  after  a  little  practice  without 
liability  of  causing  those  aberrations  due  to  the  attention  being 
drawn  to  one's  self. 

The  observations  need  not,  of  course,  be  confined  to  the  stu- 
dent's own  person ;  it  is,  however,  very  important  that  the  nor- 
mal should  be  known  before  the  observer  is  introduced  to  cases 
of  disease.  Frequent  comparison  of  the  natural  and  the  dis- 
eased condition  renders  physiology,  pathology,  and  clinical 
medicine  much  good  service.  We  again  urge  upon  the  student 
to  try  to  form  increasingly  vivid  and  correct  mental  pictures 
of  the  cirr-iilation  under  its  many  changes. 

Comparative. — An  interesting  arrangement  of  blood-vessels, 
known  as  a  rete  mirabile,  occurs  in  every  main  group  of  verte- 


284 


ANIMAL  PHYSIOLOGY. 


brates.  An  artery  breaks  up  into  a  great  number  of  vessels  of 
nearly  the  same  size,  wbicli  terminate,  abruptly  and  without 
capillaries,  in  another  arterial  trunk. 


Fig.  245.— iJeie  mirabile  of  sheep,  seen  in  profile  (after  Chauveau).  The  larger  rete  is  in  eon 
nection  with  the  encephahc  arteries ;  the  smaller,  the  ophthalmic.  The  large  artery  is  the 
carotid. 

They  are  found  in  a  variety  of  situations,  as  on  the  carotid 
and  vertebrate  arteries  of  animals  that  naturally  feed  from  the 
ground  for  long  periods  together,  as  the  ruminants ;  in  the 


Fig.  246.— Section  of  a  lymphatic  rete  mirabile,  from  the  popliteal  space  (after  Chauveau'). 
a,  a,  afferent  vessels  ;  b,  6,  efferent  vessels.  The  whole  very  strongly  suggests  a  crude 
form  of  lymphatic  gland. 


THE   CIRCULATION   OF   THE  BLOOD. 


285 


sloth,  that  hangs  from  trees ;  in  the  legs  of  swans,  geese,  etc. ;  in 
the  horse's  foot,  in  which  the  arteries  break  up  into  many  small 
divisions.  It  has  been 
suggested  that  these  ar- 
rangements permit  of  a 
supply  of  arterial  blood 
being  maintained  without 
congestion  of  the  parts. 
Very  marked  tortuosity 
of  vessels,  as  in  the  seal, 
the  carotid  of  which  is 
said  to  be  forty  times  as 
long  as  the  space  it  trav- 
erses, in  all  probability 
serves  the  same  purpose. 

Evolution.  —  The  com- 
parative sketch  we  have 
given  of  the  vascular  sys- 
tem will  doubtless  sug- 
gest a  gradual  evolution. 
We  observe  throughout  a 
dependence  and  resem- 
blance which  we  think 
can  not  be  otherwise  ex- 
plained. The  similarity 
of  the  foetal  circulation  in  the  mammal  to  the  permanent  circu- 
lation of  lower  groups  has  much  meaning.  Even  in  the  high- 
est form  of  heart  the  original  pulsatile  tube  is  not  lost.  The 
great  veins  still  contract  in  the  mammal;  the  sinus  venosus  is 
probably  the  result  of  blending  and  expansion.  The  later 
differentiations  of  the  parts  of  the  heart  are  clearly  related  to 
the  adaptation  to  altered  surroundings.  Such  is  seen  in  the 
foetal  heart  and  circulation,  and  has  probably  been  the  deter- 
mining cause  of  the  forms  which  the  circulatory  organs  have 
assumed. 

It  is  a  fact  that  the  part  of  the  heart  that  survives  the  long- 
est under  adverse  conditions  is  that  which  bears  the  stamp  of 
greatest  ancestral  antiquity.  It  (the  sinus  venosus)  may  not 
bo  less  under  nervous  control,  but  it  certainly  is  least  depend- 
ent on  the  nervous  system,  and  has  the  greatest  automaticity. 

It  is  surely  fortunate  for  man  that  this  part  of  the  reptilian 
heart  is  represented  in  his  own.  In  cases  of  fainting,  partial 
drowning,  or  other  instances  of  impending  death,  this  part,  with 


Fig.  247. 


-Veins  of  the  foot  of  the  horse  (after  Chau- 
veau). 


286  ANIMAL   PHYSIOLOGY. 

the  auricles  it  may  be,  continues  to  beat  when  the  ventricles 
have  ceased ;  and  we  have  learned  that  so  long  as  these  parts 
are  functionally  active  there  is  a  greater  probability  that  the 
quiescent  regions  may  recommence.  Activity  begets  activity, 
in  cardiac  muscle-cells  at  least.  How  are  these  facts  to  be 
explained  apart  from  evolution  ? 

The  law  of  rhythm  in  organic  nature  finds  some  of  its  most 
evident  exemplifications  in  the  circulation.  Most  of  the 
rhythms  are  compound,  one  being  blended  with  or  superim- 
posed on  another.  Even  the  apparent  irregularities  of  the  nor- 
mal heart  are  rhythmical,  such  as  the  very  marked  slowing 
and  other  changes  accompanying  expiration,  especially  in  some 
animals. 

We  trust  we  have  made  it  evident  that  the  greatest  allow- 
ance must  be  made  for  the  animal  group,  and  some  even  for 
the  individual,  in  estimating  any  one  of  the  factors  of  the  cir- 
culation. We  know  a  good  deal  at  present  of  cardiac  physiol- 
ogy, but  we  do  not  know  a  physiology  of  "  the  heart "  in  the 
sense  in  which  we  understand  that  term  to  have  been  used  till 
recently — i.  e.,  we  are  not  in  a  position  to  state  the  laws  that 
apply  to  all  forms  of  heart. 

Summary  of  the  Physiology  of  the  Circulation. — In  the  mammal 
the  circulatory  apparatus  forms  a  closed  system  consisting  of  a 
central  pump  or  heart,  arteries,  capillaries,  and  veins.  All  the 
parts  of  the  vascular  system  are  elastic,  but  this  property  is 
most  developed  in  the  arteries. 

Since  the  tissue-lymph  is  prepared  from  the  blood  in  the 
capillaries,  it  may  be  said  that  the  whole  circulatory  system 
exists  for  these  vessels. 

As  a  result  of  the  action  of  an  intermittent  pump  on  elastic 
vessels  against  peripheral  resistance,  in  consequence  of  which 
the  arteries  are  always  kept  more  than  full  (distended),  the 
flow  through  the  capillaries  and  veins  is  constant — a  very  great 
advantage,  enabling  the  capillaries  to  accomplish  their  work  of 
feeding  the  ever-hungry  tissues.  While  physical  forces  play  a 
very  prominent  part  in  the  circulation  of  the  blood,  vital  ones 
must  not  be  ignored.  They  lie  at  the  foundation  of  the  whole, 
here  as  elsewhere,  and  must  be  taken  into  the  account  in  every 
explanation. 

As  a  consequence  of  the  anatomical,  physical,  and  vital  char- 
acters of  the  circulatory  system,  it  follows  that  the  velocity  of 
the  blood  is  greatest  in  the  arteries,  least  in  the  capillaries,  and 
intermediate  in  the  veins. 


THE  CIRCULATION   OF   THE   BLOOD.  287 

The  veins  with  their  valves,  their  superficial  position  and 
thinner  walls,  make  up  a  set  of  conditions  favoring  the  onflow 
of  the  blood,  especially  under  muscular  exercise. 

In  the  mammal  tlie  circulatory  system,  by  reason  of  its  con- 
nections with  the  digestive,  respiratory,  and  lymphatic  systems, 
and  in  a  lesser  degree  with  all  parts  of  the  body,  especially  the 
glandular  organs,  maintains  at  once  the  usefulness  and  the  fit- 
ness of  the  blood. 

The  arterioles,  by  virtue  of  their  highly  developed  muscular 
coat,  are  enabled  to  regulate  the  blood-supply  to  every  part,  in 
obedience  to  the  nervous  system. 

The  blood  exercises  a  certain  pressure  on  the  walls  of  all 
parts  of  the  vascular  system,  which  is  greatest  in  the  heart  it- 
self, high  in  the  arteries,  lower  in  the  capillaries,  and  lowest  in 
the  veins,  in  the  largest  of  which  it  may  be  less  than  the  atmos- 
pheric pressure,  or  negative.  The  heart  in  the  mammal  consists 
of  four  perfectly  separated  chambers,  each  upper  and  each 
lower  pair  working  synchronously,  intermixture  of  arterial 
and  venous  blood  being  prevented  by  septa  and  interference  in 
working  by  valves.  The  heart  is  a  force-pump  chiefly,  but,  to 
some  extent,  a  suction-pump  also,  though  its  power  as  such 
purely  from  its  own  action  and  independent  of  the  respiratory 
movements  of  the  chest  is  slight  under  ordinary  circumstances. 
In  consequence  of  the  lesser  resistance  in  the  pulmonary  divis- 
ion of  the  circulation,  the  blood-pressure  within  the  heart  is 
much  less  in  the  right  than  in  the  left  ventricle — a  fact  in  har- 
mony with  and  causative  of  the  greater  thickness  of  the  walls 
of  the  latter ;  for  in  the  foetus,  in  which  the  conditions  are  dif- 
ferent, this  distinction  does  not  hold. 

The  ventricles  usually  completely  empty  themselves  of 
blood  and  maintain  their  systolic  contraction  even  after  this 
has  been  effected.  The  contraction  of  the  heart,  which  really 
begins  in  the  great  veins  near  their  junction  with  the  auricles 
(that  do  not  fully  empty  themselves),  is  at  once  followed  up  by 
the  auricular  and  ventricular  contraction,  the  whole  constitu- 
ting one  long  peristaltic  wave.  Then  follows  the  cardiac  pause, 
which  is  of  longer  duration  than  the  entire  systole. 

When  the  heart  contracts  it  hardens,  owing  to  closing  on  a 
non-compressible  fluid  dammed  back  within  its  walls  by  resist- 
ance a  fronte.  At  the  same  time  the  hand  y^laced  on  the  chest- 
walls  over  the  heart  is  sensible  of  the  cardiac  impulse,  owing 
to  what  has  just  Ixien  mentioned.  The  systole  of  the  chambers 
of  the  heart  gives  rise  to  a  first  and  a  second  sound,  so  called, 


288  ANIMAL   PHYSIOLOGY. 

caused  by  several  events  combined,  in  whicb,  however,  the  ten- 
sion of  the  valves  must  take  a  prominent  share.  The  work  of 
the  heart  is  dependent  on  the  quantity  of  blood  it  ejects  and 
the  pressure  against  which  it  acts.  The  pulse  is  an  elevation 
of  the  arterial  wall,  occurring  with  each  heart-beat,  in  conse- 
quence of  the  passage  of  a  wave  over  the  general  blood-stream. 
There  is  a  distention  of  the  entire  arterial  system  in  every  di- 
rection. The  pulse  travels  with  extreme  velocity  as  compared 
with  the  blood-current.  The  heart-beat  varies  in  force,  fre- 
quency, duration,  etc.,  and  with  age,  sex,  posture,  and  numer- 
ous other  circumstances. 

The  whole  of  the  circulatory  system  is  regulated  by  the  cen- 
tral nervous  system  through  nerves.  There  is  in  the  medulla 
oblongata  a  small  collection  of  nerve-cells  making  up  the 
cardio-inhibitory  center.  This  center,  with  varying  degrees  of 
constancy,  depending  on  the  group  of  animals  and  the  needs 
of  the  organism,  sends  forth  impulses  (which  modify  the  beat 
of  the  heart  in  force  and  frequency)  through  the  vagi  nerves. 
There  are  nerves  of  the  sympathetic  system  with  a  center  in 
the  cervical  spinal  cord,  and  possibly  another  in  the  medulla, 
which  are  capable  of  originating  either  an  acceleration  of  the 
heart-rhythm  or  an  increase  of  the  force  of  the  beat,  or  both 
together,  known  as  accelerators  or  augmentors.  In  the  verte- 
brates thus  far  examined  the  vagus  is  in  reality  a  vago-sympa- 
thetic  nerve,  containing  inhibitory  fibers  proper,  and  sympa- 
thetic, accelerator,  or  motor  fibers. 

The  inhibitory  fibers  can  arrest,  slow,  or  weaken  the  cardiac 
beat;  the  sympathetic  accelerate  it  or  augment  its  force. 
When  both  are  stimulated  together,  the  inhibitory  prevail.     . 

These  nerves,  as  also  the  accelerators,  exercise  a  profound 
influence  upon  the  nutrition  of  the  heart,  and  effect  its  electri- 
cal condition  when  stimulated,  and  we  may  believe  when  influ- 
enced by  their  own  centers. 

The  inhibitory  fibers  tend  to  preserve  and  restore  cardiac 
energy ;  the  sympathetic,  whether  in  the  vagus  or  as  the  aug- 
mentors, the  reverse.  The  vagus  nerve  (and  probably  the  de- 
pressor) acts  as  an  afferent,  cardiac  sensory  nerve  reporting  on 
the  intra  -  cardiac  pressure,  etc.,  and  so  enabling  the  vaso- 
motor and  cardio-inhibitory  centers,  which  are,  it  would  seem, 
capable  of  related  and  harmonious  action  to  act  for  the  general 
good. 

The  arterioles  must  be  conceived  as  undergoing  very  fre- 
quent changes  of  caliber.     They  are  governed  by  the  vase- 


THE  CIRCULATION  OF  THE  BLOOD.  289 

motor  center,  situated  in  the  medulla,  and  possibly  certain  sub- 
ordinate centers  in  the  spinal  cord,  through  vaso-motor  nerves. 
These  are  (a)  vaso-constrictors,  which  maintain  a  constant  but 
variable  degree  of  contraction  of  the  muscle-cells  of  the  vessels ; 
(6)  vaso-dilators,  which  are  not  in  constant  functional  activity ; 
and  (c)  mixed  nerves,  with  both  kinds.  An  inherited  tendency 
to  rhythmical  contraction  throughout  the  entire  vascular  sys- 
tem, including  the  vessels,  must  be  taken  into  account. 

The  depressor  nerve  acts  by  lessening  the  tonic  contraction 
of  (dilating)  the  vessels  of  the  splanchnic  area  especially. 

It  is  important  to  remember  that  all  the  changes  of  the 
vascular  system,  so  long  as  the  nervous  system  is  intact — i.  e., 
so  long  as  an  animal  is  normal — are  correlated ;  and  that  the 
action  of  such  nerves  as  the  depressor  is  to  be  taken  rather  as 
an  example  of  how  some  of  these  changes  are  brought  about, 
mere  chapters  in  an  incomplete  but  voluminous  history,  if  we 
could  but  write  it  all.  The  changes  in  blood-pressure,  by  the 
addition  or  removal  of  a  considerable  quantity  of  blood,  are 
slight,  owing  to  the  sort  of  adaptation  referred  to  above,  effected 
through  the  nervous  system.  Finally,  the  capillary  circulation, 
when  studied  microscopically,  and  especially  in  disordered  con- 
ditions, shows  clearly  that  the  vital  properties  of  these  vessels 
have  an  important  share  in  determining  the  character  of  the 
circulation  in  themselves  directly  and  elsewhere  indirectly. 

The  study  of  the  circulation  in  other  groups  shows  that 
below  birds  the  arterial  and  venous  blood  undergoes  mixture 
somewhere,  usually  in  the  heart,  but  that  in  all  the  vertebrates 
the  best  blood  is  invariably  that  which  passes  to  the  head  and 
upper  regions  of  the  body.  The  deficiencies  in  the  heart,  owing 
to  the  imperfections  of  valves,  septa,  etc.,  are  in  part  counter- 
acted in  some  groups  by  pressure  relations,  the  blood  always 
flowing  in  the  direction  of  least  resistance,  so  that  the  above- 
mentioned  result  is  achieved. 

Caj)illaries  are  wanting  in  most  of  the  invertebrates,  the 
blood  flowing  from  the  arteries  into  spaces  (sinuses)  in  tlie  tis- 
sues. It  is  to  be  noted  that  a  modified  blood  (lymph)  is  also 
found  in  the  interspaces  of  the  cells  of  organs.  Indeed,  the 
circulatoi-y  system  of  lower  forms  is  in  many  respects  analogous 
to  the  lymj^hatic  system  of  higher  ones. 
19 


290  ANIMAL  PHYSIOLOGY. 


DIGESTION  OF  FOOD. 

The  processes  of  digestion  may  be  considered  as  having 
for  their  end  the  preparation  of  food  for  entrance  into  the 
blood. 

This  is  in  part  attained  when  the  insoluble  parts  have  been 
rendered  soluble.  At  this  stage  it  becomes  necessary  to  inquire 
as  to  what  constitutes  food  or  a  food. 

Inasmuch  as  animals,  unlike  plants,  derive  none  of  their 
food  from  the  atmosphere,  it  is  manifest  that  what  they  take  in 
by  the  mouth  must  contain  every  chemical  element,  in  some 
form,  that  enters  into  the  composition  of  the  body. 

But  actual  experience  demonstrates  that  the  food  of  animals 
must,  if  we  except  certain  salts,  be  in  organized  form — i.  e.,  it 
must  approximate  to  the  condition  of  the  tissues  of  the  body  in 
a  large  degree.  Plants,  in  fact,  are  necessary  to  animals  in 
working  up  the  elements  of  the  earth  and  air  into  form  suit- 
able for  them. 

Foodstuffs  are  divisible  into  : 

I.  Organic. 

1.  Nitrogenous. 

(a.)  Albumins. 

(6.)  Albuminoids  (as  gelatine). 

2.  Non-nitrogenous. 

(a.)  Carbohydrates  (sugars,  starches). 
(Z>.)  Fats. 

II.  Inorganic. 

1.  Water, 

2.  Salts. 

Animals  may  derive  the  whole  of  their  food  from  the 
bodies  of  other  animals  (carnivora) ;  from  vegetable  matter 
exclusively  {herbivora) ;  or  from  a  mixture  of  the  animal  and 
vegetable,  as  in  the  case  of  the  pig,  bear,  and  man  himself 
{omnivora). 

It  has  been  found  by  feeding  experiments,  carried  out  mostly 
on  dogs,  that  animals  die  when  they  lack  any  one  of  the  con- 
stituents of  food,  though  they  live  longer  on  the  nitrogenous 
than  any  other  kind.  In  some  instances,  as  when  fed  on  gela- 
tine and  water,  or  sugar  and  water,  the  animals  died  almost  as 
soon  as  if  they  had  been  wholly  deprived  of  food.  But  it  has 
also  been  observed  that  some  animals  will  all  but  starve  rather 
than  eat  certain  kinds  of  food,  though  chemically  sufficient. 


DIGESTION   OF   POOD. 


291 


We  must  thus  recognize  something  more  in  an  animal  than 
merely  the  mechanical  and  chemical  processes  which  suffice  to 
accomplish  digestion  in  the  laboratory.  A  food  must  be  not 
only  sufficient  from  the  chemical  and  physical  point  of  view, 
but  be  capable  of  being  acted  on  by  the  digestive  juices,  and 
of  such  a  nature  as  to  suit  the  particular  animal  that  eats  it. 

To  illustrate,  bones  may  be  masticated  and  readily  digested 
by  a  hyena,  but  not  by  an  ox  or  by  man,  though  they  meet  the 
conditions  of  a  food  in  containing  all  the  requisite  constituents. 
Further,  the  food  that  one  man  digests  readily  is  scarcely  digesti- 
ble at  all  by  another ;  and  it  is  within  the  experience  of  every 
one  that  a  frequent  change  of  diet  is  absolutely  necessary. 

Since  all  mammals,  for  a  considerable  period  of  their  exist- 
ence, feed  upon  milk  exclusively,  this  must  represent  a  perfect 
or  typical  food.  It  will  be  worth  while  to  examine  the  compo- 
sition of  milk.  The  various  substances  composing  it,  and  their 
relative  proportions  for  different  animals,  may  be  seen  from  the 
following  table,  which  is  based  on  a  total  of  1,000  parts : 


CONSTITUENTS. 

Hnmau. 

Cow. 

Goat. 

Ass. 

Water 

889  08 

857-05 

863-58 

910-24 

Casein 

Albumin 

Butter 

39-24 

26-66 

43-64 

1-38 

j       48-28 

}        5-76 

43-05 

40-37 

5-48 

33-60 
12-99 
43-57 
40-04 
6-22 

I      20-18 
12-56 

Milk-sugar  .    .          

Salts 

[      57-02 

Total  solids 

110-92 

142-95 

136-43 

89-76 

The  fact  that  human  milk  is  poorer  in  proteids  and  fats 
especially  is  of  practical  importance,  for,  when  cow's  milk  is  sub- 
stituted in  the  feeding  of  infants,  it  should  be  diluted,  and  sugar 
and  cream  added  if  the  normal  proportions  of  mother's  milk 
are  to  be  retained. 

1.  The  proteids  of  milk  are : 

(a.)  An  albumin  very  like  serum-albumin. 

(b.)  Casein,  normally  in  suspension,  in  the  form  of  extremely 
minute  particles,  which  contributes  to  the  opacity  of  milk. 

It  can  be  removed  by  filtration  through  porcelain  ;  and  pre- 
cipitated or  coagulated  by  acids  and  by  rennet,  an  extract  of 
the  mucous  membrane  of  the  calf's  stomach.  After  this  coagu- 
lation, whey,  a  fluid  more  or  loss  clear,  separates,  which  con- 
tains the  salts  and  sugar  of  milk  and  most  of  tlie  water.  Much 
of  the  fat  is  entangled  with  the  casein. 


292  ANIMAL   PHYSIOLOGY. 

Casein,  with  some  fat,  makes  up  the  greater  part  of  cheese. 

2.  Fats. — Milk  is  an  emnlsion — i.  e.,  contains  fat  suspended 
in  a  fine  state  of  division.  The  globules,  which  vary  greatly  in 
size,  are  surrounded  by  an  envelope  of  proteid  matter.  This 
covering  is  broken  up  by  churning,  allowing  the  fatty  globules 
to  run  together  and  form  butter. 

Butter  consists  chiefly  of  olein,  palmitin,  and  stearin,  but 
contains  in  smaller  quantity  a  variety  of  other  fats.  The  ran- 
cidity of  butter  is  due  to  the  presence  of  free  fatty  acids,  espe- 
cially butyric. 

The  fat  of  milk  usually  rises  to  the  surface  as  cream  when 
milk  is  allowed  to  stand. 

3.  Milk-sugar,  which  is  converted  into  lactic  acid,  probably 
by  the  agency  of  some  form  of  micro-organism,  thus  furnish- 
ing acid  sufficient  to  cause  the  precipitation  or  coagulation  of 
the  casein. 

Milk-sugar.        Lactic  acid. 
CgHiaOe  =  2C3H8O3 

Milk,  when  fresh,  should  be  neutral  or  faintly  alkaline. 

4.  Salts  (and  other  extractives),  consisting  of  phosphates  of 
calcium,  potassium,  and  magnesium,  potassium  chloride,  with 
traces  of  iron  and  other  substances. 

It  can  be  readily  understood  why  children  fed  on  milk  rarely 
suffer  from  that  deficiency  of  calcium  salts  in  the  bones  leading 
to  rickets,  so  common  in  ill-fed  children.  It  thus  appears  that 
milk  contains  all  the  constituents  requisite  for  the  building  up 
of  the  healthy  mammalian  body ;  and  experiments  prove  that 
these  exist  in  proper  proportions  and  in  a  readily  digestible 
form.  The  author  has  found  that  a  large  number  of  animals, 
into  the  usual  food  of  which,  in  the  adult  form,  milk  does  not 
enter,  like  most  of  our  wild  mammals,  as  well  as  most  birds, 
will  not  only  take  milk  but  soon  learn  to  like  it,  and  thrive  well 
upon  it.  Since  the  embryo  chick  lives  upon  the  egg,  it  might 
have  been  supposed  that  eggs  would  form  excellent  food  for 
adult  animals,  and  common  experience  proves  this  to  be  the 
case ;  while  chemical  analysis  shows  that  they,  like  milk,  con- 
tain all  the  necessary  food  constituents.  Meat  (muscle,  with 
fat  chiefly)  is  also,  of  course,  a  valuable  food,  abounding  in 
proteids.  Cereals  contain  starch  in  large  proportion,  but  also  a 
mixture  of  proteids.  Green  vegetables  contain  little  actual  nu- 
tritive material,  but  are  useful  in  furnishing  salts  and  special 
substances,  as  certain  compounds  of  sulphur  which,  in  some  ill- 
understood  way,  act  beneficially  on  the  metabolism  of  the  body.' 


DIGESTION   OF   FOOD. 


293 


They  also  seem  to  stimulate  the  flow  of  healthy  digestive  fluids. 
Condiments  act  chiefly,  perhaps,  in  the  latter  way.  Tea,  coffee, 
etc.,  contain  alkaloids,  which  it  is  likely  have  a  conservative 
effect  on  tissue  waste,  but  we  really  know  very  little  as  to  how 
it  is  that  they  prove  so  beneficial.  Though  they  are  recognized 
to  have  a  powerful  effect  on  the  nervous  system  as  stimulants, 
nevertheless  it  would  be  erroneous  to  suppose  that  their  action 
was  confined  to  this  alone. 

Animal  Foods. 
Explanation  of  the  signs. 


Beef. 
Pork. 
Fowl. 
Fixh. 

Egg. 
Cou-'s  milh. 
Human  milk. 


Proteids.    Albuminoids.    N-free  org.  bodies.        Salts. 


i5  !  5 


1-5 

3' 


U'.5     '  i-Hl^.f]  1.3 


73.5 


HHo.o 

1110.4 


Wheaten-bread. 

Peas. 

Rice. 

Potatoes. 

WhiU  Turnip. 

CauHflt/wer. 

lieer. 


Vegetable  Foods. 

Explanation  of  the  signs. 


Digestible        Non-digestible  Salts. 

N-free  organ  bodies. 

m 


90.5 


90 


90 


FiQ.  348  (Landois). 


0.5 


1' 


0.5 


Hm^ 


31II«-' 


The  accompanying  diagrams  will  serve  to  represent  to  the 
eye  the  relative  proportions  of  the  food-essentials  in  various 
kinds  of  articles  of  diet. 


294 


ANIMAL   PHYSIOLOGY. 


It  is  plain  that  if,  in  the  digestive  tract,  foods  are  changed 
in  solubility  and  actual  chemical  constitution,  this  must  have 


Fig.  349.— Alimentary  canal  of  embryo  while  the  rudimentary  mid-gut  is  stiU  in  continuity 
with  yelk-sac  (Kolliker,  after  BischofC).  A.  View  from  .before,  a,  pharyngeal  plates  ;  6, 
pharynx  \  c,  c,  diverticula  forming  the  lungs ;  d,  stomach  ;  /,  diverticula  of  liver ;  g. 
membrane  torn  from  yelk-sac  ;  h,  hind-gut.  B.  Longitudinal  section,  a,  diverticulum  of 
a  lung  ;  6,  stomach  ;  c,  liver  ;  d,  yelk-sac. 

been  brought  about  by  chemical  agencies.  That  food  is  broken 
up  at  the  very  commencement  of  the  alimentary  tract  is  a 
matter  of  common  observation;  and  that  there  should  be  a 
gradual  movement  of  the  food  from  one  part  of  the  canal  to 


Fig.  250. 


Fig.  251. 


Fig.  250.— Diagram  of  alimentary  canal  of  chick  at  fourth  day  (Foster  and  Balfour,  after 
Gotte).    Ig,  diverticulum  of  one  lung  ;  St,  stomach  ;  I,  liver  ;  p,  pancreas. 

Fig.  251.— Position  of  various  parts  of  alimentary  canal  at  different  stages.  A.  Embryo  of 
five  weeks.  B.  Of  eight  weeks.  C.  Of  ten  weeks  (Allen  Thompson).  I,  pharynx  with  the 
lungs  ;  .s,  stomach  ;  i",  small  intestine ;  i\  large  intestine  ;  gr,  genital  duct ;  u,  bladder  ; 
cl,  cloaca  ;  c,  csecimi ;  vi,  ductus  vitello-intestinalis  ;  si,  urogenital  sinus  ;  v,  yelk-sac. 


DIGESTION   OF   FOOD. 


295 


another,  where  a  different  fluid  is  secreted,  would  be  expected. 
As  a  matter  of  fact,  mechanical  and  chemical  forces  play  a 
large  part  in  the  actual  preparation  of  the  food  for  absorption. 
Behind  these  lie,  of  course,  the  vital  properties  of  the  glands, 
which  prepare  the  active  fluids  from  the  blood,  so  that  a  study 
of  digestion  naturally  divides  itself  into  the  consideration  of — 


B^G.  252. — Ammothea  pycnogonides,  a  marine  animal  (after  Quatrefages).    ce,  cesophagus ; 
o,  antennae  ;  s,  stomach,  with  prolongations  into  antennae  and  limbs  (I). 

1.  The  digestive  juices;  2.  The  secretory  processes ;  and,  3.  The 
muscular  and  nervous  mechanism  by  which  the  food  is  carried 
from  one  part  of  the  digestive  tract  to  another,  and  the  waste 
matte?  finally  expelled. 


:2i.^^^ 


Fio.  253.— Ixjngitudinal  vertical  section  of  body  of  leech,  Hirudo  niedicinalis  (After  Leuckart). 
a,  mrtutb  :  Ij,  h,  h,  Hacculation.s  of  alimentary  canal ;  c,  anus  ;  d,  terminal  sucker  ;  e,  cere- 
bral ganglia  ;  /,  /',  chain  of  post-u^sr^phageal  ganglia  ;  r/,  g,  g,  segmental  organs. 

Embryological. — Tlic  alimentary  tract,  as  we  have  seen,  is 
fornic'i  by  ;iii  infolding  of  tlu;  splanchnopleure,  and,  according 
as  the  growth  is  more  or  less  marked,  does  the  canal  become 


296  ANIMAL  PHYSIOLOGY. 

iortuous  or  remain  somewliat  straight.  The  alimentary  tract 
of  a  mammal  passes  through  stages  of  development  which  cor- 
respond with  the  permanent  form  of  other  groups  of  verte- 
brates, according  to  a  general  law  of  evolution.  Inasmuch  as 
the  embryonic  gut  is  formed  of  mesoblast  and  hypoblast,  it  is 
easy -to  understand  why  the  developed  tract  should  so  invaria- 
bly consist  of  glandular  structures  and  muscular  tissue  dis- 
posed in  a  certain  regular  arrangement.     The  fact  that  all  the 


Fig.  254. — Portion  of  a  jelly-flsh,  the  Medusa  Aurelia,  showing  gastro-vascular  canals  radi- 
ating from  central  stomach  and  terminating  in  a  circular  marginal  canal  (after  Romanes). 
All  these  are  shaded  very  dark  ;  the  light  spaces  indicate  artificial  sections.  Inasmuch  as 
these  canals  as  well  as  the  stomach  must  contain  some  sea-water,  and  since  their  contents 
represent  the  whole  of  the  nutritive  fluid  (answering  to  the  blood.  l.ymph,  and  chyle  of 
higher  forms),  we  have  both  anatomically  and  physiologically  a  very  crude  or  undifferen- 
tiated condition  in  such  animals,  and  one  of  great  interest  from  an  evolutionary  point  of 
view. 

organs  that  pour  digestive  juices  into  the  alimentary  tract  are 
outgrowths  from  it  serves  to  explain  why  there  should  remain 
a  physiological  connection  with  an  anatomical  isolation.  The 
general  resemblance  of  the  epithelium  throughout,  even  in 
parts  widely  separated,  also  becomes  clear,  as  well  as  many 
otter  points  we  can  not  now  refer  to  in  detail,  to  one  who 
realizes  the  significance  of  the  laws  of  descent  (evolution). 

Comparative. — Amoeba  ingests  and  digests  apparently  by 
every  part  of  its  body ;  though  exact  studies  have  shown  that 
it  neither  accepts  nor  retains  without  considerable  power  of 


DIGESTION   OP  FOOD. 


2y: 


discrimination ;  and  it  is  also  possible  that  some  sort  of  digest- 
ive fluid  may  be  secreted  from  the  part  of  the  body  with  which 
the  food-particles  come  in  contact.  It  has  been  shown,  too, 
that  there  are  differences  in  the  digestive  capacity  of  closely 
allied  forms  among  Infiisorians. 

The  ciliated  Infusorians  have  a  permanent  mouth,  which 
may  also  serve  as  an  anus ;  or,  there  may  be  an  anus,  though , 
usually  less  distinct  from  the  rest  of  the  body  than  the  mouth. 

Among  the  Coelenterates  inira-cellular  digestion  is  found. 
Certain  cells  of  the  endoderm  (as  in  Hydra)  take  up  food-parti- 


Fio.  '2T)T).—\  jflly-fish,  the  Mcduna  TJninnrodium  (aft^r  Allman).  Note  the  lotiR  proljoscif; 
^rnouth)  \ftu\\nv;  iir>  to  th«*  Ktoinach,  frnm  which  radiate  the  pastro-vasciilar  canals.  A 
fKirtion  of  the  b»-ll  haw  Ix-eri  removed,  shfiwinj;  the  generative  arranged  around  the 
diKCHtive  organs.     Most  of  the  tentacles  are  turned  up. 


ch'K  Ama'})a-like,  digest  them,  and  thus  ])rovicle  material  for 
other  cells  as  well  as  thcmselvf^s,  in  a  form  suitable  for  assimi- 
lation.   This  is  a  beginning  of  that  differentiation  of  function 


298 


ANIMAL   PHYSIOLOGY. 


which  is  carried  so  far  among  the  higher  vertebrates.  But,  as 
recent  investigations  have  shown,  such  intra-cellular  digestion 
exists  to  some  extent  in  the  alimentary  canal  of  the  highest 
members  of  the  vertebrate  groap  (see  page  345). 

The  means  for  grasping  and  triturating  food  among  in- 
vertebrates are  very  complicated  and  varied,  as  are  also  those 
adapted  for  sucking  the  juices  of  prey.  Examples  to  hand  are 
to  be  found  in  the  crab,  crayfish,  spider,  grasshopper,  beetle, 


Fig.  256.— Diagram  illustrating  arrangement  of  intestine,  nervous  system,  etc.,  in  common 
snail.  Helix  (after  Huxley),  m,  mouth  ;  t,  tooth ;  od,  odontophore ;  g,  gullet ;  c,  crop  ; 
s,  stomach  ;  r,  rectum  ;  a,  anus  ;  r.  s,  renal  sac  ;  /i,  heart ;  I,  lung  (modified  pallial  cham- 
ber) ;  11,  its  external  aperture  ;  em,  thick  edge  of  mantle  united  with  sides  of  body  :  /, 
foot ;  cpg,  cerebral,  pedal,  and  parieto-splancnnic  ganglia  aggregated  round  gullet. 


etc.,  on  the  one  hand,  and  the  butterfly,  house-fly,  leech,  etc., 
on  the  other. 

The  digestive  system  of  the  earth-worm  has  been  studied 
with  some  care.  It  illustrates  a  sort  of  extra-corporeal  diges- 
tion, in  that  it  secretes  a  fluid  from  the  mouth  which  seems 'to 
act  both  chemically  and  mechanically  on  the  starch-grains 
of  the  leaves  on  which  it  feeds.  It  is  provided  with  an  organ 
in  which,  as  with  birds,  small  stones  are  found,  so  that  the 
imperfections  of  its  mouth  are  compensated  for  by  this  gizzard 
which  triturates  the  food.  Its  calciferous  glands  supply  the 
alkaline  fluids  necessary  to  neutralize  the  humus  acids  of  de- 
caying leaves,  for  intestinal  digestion  only  proceeds  in  an  alka- 
line medium. 

The  gastric  mill  of  a  crab  (Fig.  228)  is  a  provision  of  ob- 
vious value  in  so  voracious  a  creature. 


DIGESTION   OF   FOOD. 


299 


Pal  > ^ 


=5  -  2  m  5« 


Before  passing  on  to  higher  groups,  it  will  be  well  to  bear 
in  mind  that  the  digestive  organs  are  to  be  regarded  as  the  out- 
come both  of  he- 
redity and  adap- 
tation to  circum- 
stances. We  find 
parts  of  the  in- 
testine, e,  g.,  re- 
tained in  some 
animals  in  whose 
economy  they 
seem  to  serve 
little  if  any  good 
purpose,  as  the 
vermiform  ap- 
pendix of  man. 
Adaptation  has 
been  illustrated 
in  the  lifetime 
of  a  single  indi- 
vidual in  a  re- 
markable man- 
ner ;  thus,  a  sea- 
gull, by  being  fed 
on  grain,  has  had 
its  stomach,  nat- 
urally thin  and 
soft-walled,  con- 
verted into  a 
muscular  giz- 
zard. 

Since  diges- 
tion is  a  process 
in  which  the 
mechanical  and 
chemical  are 
both  involved, 
and  tlni  food  of 
animuls     differs 

so  widely,  great  variety  in  the  alimentary  tract,  both  ana- 
tomical and  pliysiologicul,  must  be  (jxpected.  Vegetable  food 
must  usually  be  eat(;n  in  miu-h  larger  bulk  to  furnish  the 
needed  elements;  hence  the  great  length  of  intestine  habitually 


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300 


ANIMAL   PHYSIOLOGY. 


found  in  herbiivorons  animals,  associated  often  with,  a  capacious 
and   chambered  stomach,   furnishing  a  larger  laboratory  in 


Fig.  258.— The  viscera  of  a  rabbit  as  seen  upon  simply  opening  the  cavities  of  the  thorax  and 
abdomen  without  any  further  dissection.  A,  cavity  of  the  thorax,  pleural  cavity  on  either 
side  ;  B,  diaphragm  ;  C,  ventricles  of  the  heart ;  D,  auricles  ;  E,  pulmonary  artery ;  F", 
aorta  ;  G,  lungs  collapsed,  and  occupying  only  back  part  of  chest ;  H,  lateral  portions  of 
pleural  membranes  ;  /,  cartilage  at  the  end  of  sternum  (ensiform  cartilage) ;  K,  portion 
of  the  waU  of  body  left  between  thorax  and  abdomen  ;  a,  cut  ends  of  the  ribs  ;  L,  the 
liver,  in  this  case  lying  more  to  the  left  than  to  the  right  of  the  body  ;  M,  the  stomach,  a 
large  part  of  the  greater  curvature  being  shown  ;  N,  duodenum  ;  O,  small  intestine  ;  P, 
the  caecum,  so  largely  developed  in  this  and  other  herbivorous  animals  ;  Q,  the  large 
intestine.    (Huxley.) 

which  Nature  may  carry  on  her  processes.  To  illustrate,  the 
stomach  of  the  ruminants  consists  of  four  parts  {rumen,  reticu- 
lum, omasum  (psalterium,),  dbomasum).  The  food  when  cropped 
is  immediately  swallowed ;  so  that  the  paunch  {rumen)  is  a 
mere  storehouse  in  which  it  is  softened,  though  but  little 
changed  otherwise ;  and  it  would  seem  that  real  gastric  di- 


DIGESTION  OF   POOD. 


301 


gestioii  is  almost  confined  to  the  last  division,  which  may  be 
compared  to  the  simple  stomach  of  the  Carnivora  or  of  man ; 
and,  before  the  food  reaches  this  region,  it  has  been  thoroughly 
masticated  and  mixed  with  saliva. 


Fig.  259.— Stomach,   ii.n   i  lu^.    iiit(«.tine,  etc    (aft<'r  Sapjx-y)      1,  anterior  surface  of 

liver;  2.  (^all-bluiM'i  ,    ^  ition  of  diaphraKiii  :  4,  postciior  '-uiface  of  stomach;  5, 

lobas  Rpiffelii  of  liver  .  0,  uelidc  axis  ,  7,  coionary  arter\  of  stoiiiath  ;  8,  splenic  art«ry  ; 
9.  spleen:  10.  pancreas,  11,  isupcnor  nn-st-ntcriu  vmnt-ln  ;  12,  Juoclenuni  ;  13,  upper  ex- 
tremity of  small  intestine  ;  14,  lower  end  of  ileum  ;  1.5,  1.5,  mesentery  ;  16,  cajcum  ;  17, 
apjjendix   vermiformis  :    18,  ascending:  colon  ;    19,  19,  transverse  colon  ;   20,  descending 


colon  ;  21,  sijrmoid  flexure  of  colon  ;  22,  rectum  ;  23,  urinary  bladder. 


The  reticulum  is  especially  adapted  for  holding  water,  which 
may  serve  a  good  purpose  in  moistening  and  thinning  the  con- 
tents of  the  stomach.  In  the  camels  and  llamas  a  portion  of 
the  stomach  is  made  up  of  pouches,  which  can  be  closed  with 
sphincter  muschis,  and  thus  shut  off  tlie  water-supply  in  s(?p- 
arate  tanks,  as  it  w(^re. 

The  stomach  of  th(!  horse  is  small,  though  the;  intestine, 
especially  the  large  gut,  is  (;aj)acious. 

Tlif  stomach  is  divisible  into  a  cardiac  region,  of  a  light 
color  internally,  and  lined  witli  epithelium,  like  that  of  the 


302 


ANIMAL   PHYSIOLOGY. 


Fig.  260.— a.  Stomach  of  sheep.    B.  Stomach  of  musk-deer,    ce,  oesophagus ;  Rn,  rumen ; 
Bet,  reticulum  ;  Ps,  psalterium  ;  A,  Ab,  abomasum  ;  Du,  duodenum  ;  Py.  pylorus  (Huxley). 


Fig.  261.— Stomach  of  horse  (after  ChauveauV      A,  cardiac  extremity  of  oesophagus;  B, 

pyloric  ring. 


DIGESTION   OF   FOOD. 


303 


oesophagus,  and  a  redder  pyloric  area,  in  which  the  greater 
part  of  the  digestive  process  goes  on. 


Fic;.  262.-  Stomach  of  dog  (after  C'liauvi-aui.     . I ,  oesophagus  ;  S,  pylorus. 


The  mouth  parts,  even  in  some  of  the  higher  vertebrates,  as 
the  Carnii'ora,  serve  a  prehensile  rather  than  a  digestive  pur- 
pose. This  is  well  seen  in  the  dog,  that  bolts  his  food ;  but 
in  this  and  allied  groups  of  mammals  gastric  digestion  is  very 
active. 


Fig.  2C3.— General  and  lateral  view  of  dog"H  teeth  (aft»'r  (!hauvcaii). 


304 


ANIMAL   PHYSIOLOGY. 


The  teeth,  as  triturating  organs  find  their  highest  develop- 
ment in  ruminants,  the  combined  side-to-side  and  forward-and- 
backward  motion  of  the  jaws  rendering  them  very  effective. 


Fig.  265. 


Fig.  264. 

Fig.  264.— Dentition  of  inferior  jaw  of  horse  (after  Chauveau). 

Fig.  265. — Inferior  maxilla  of  man  (after  Sappey).    Alveolar  border ;  /,  incisor  teeth ;  c,  canine 
teeth  ;  6,  bicuspid  teeth  ;  m,  molars. 


In  Carnivora  the  teeth  serve  for  grasping  and  tearing,  while 
in  the  Insectivora  the  tongue,  as  also  in  certain  birds  (wood- 
peckers), is  an  important  organ  for  securing  food. 

It  is  to  be  noted,  too,  that,  while  the  horse  crops  grass  by 
biting  it  off,  the  ox  uses  the  tongue,  as  well  as  the  teeth  and 
lips,  to  secure  the  mouthful. 


DIGESTION  OP  FOOD. 


305 


Fio.  2WJ. — dcncral  view  of  (lij."'stivp  apparatiiH  of  fowl  faflcr  Chnuvcaui.  1,  tnnpiie  ;  2, 
pharynx:  3.  first.  iKirtion  of  <i?w)plia(rus ;  4,  crop;  r>,  wcfiiid  portion  of  <i>sopliii(;iis  :  fi, 
Buccentric  v«ntricl(?  (prov<?ntri(;uluH) ;  7,  gizzard  ;  8,  origin  of  iluodcnniii ;  !),  first  hraiicli 

20 


306  ANIMAL   PHYSIOLOGY. 

of  duodenal  flexure  ;  10,  second  branch  of  same ;  11,  origin  of  floating  portion  of  small 
intestine  ;  12,  small  intestine  ;  12',  terminal  portion  of  this  intestine,  flanked  on  each  side 
by  the  two  caeca  (regarded  as  the  analogue  of  colon  of  mammals) ;  13,  13,  free  extremities 
of  caecums  ;  14,  insertion  of  these  two  culs-de-sac  into  intestinal  tube  ;  15,  rectum  ;  16, 
cloaca  ;  17,  anus ;  18,  mesentery  ;  19,  left  lobe  of  liver  ;  20,  right  lobe  ;  21,  gall-bladder ; 
22,  insertion  of  pancreatic  and  biliary  ducts  ;  the  two  pancreatic  ducts  are  the  most  ante- 
rior, the  choledic  or  hepatic  is  in  the  middle,  and  the  cystic  duct  is  posterior ;  23.  pancreas; 
24,  diaphragmatic  aspect  of  lung  ;  25,  ovary  (in  a  state  of  atrophy) ;  26,  oviduct. 

Man's  teeth  are  somewliat  intermediate  in  form  between  the 
carnivorous  and  the  herbivorous  type.  Birds  lack  teeth,  but 
the  strong  muscular  gizzard  suffices  to  grind  the  food  against 
the  small  pebbles  that  are  habitually"  swallowed. 

The  crop,  well  developed  in.  granivorous  birds,  is  a  dilata- 
tion of  the  oesophagus,  serving  to  store  and  soften  the  food. 

In  the  pigeon  a  glandular  epithelium  in  the  crop  secretes  a 
milky-looking  substance,  that  is  regurgitated  into  the  mouth 
of  the  young  one,  which  is  inserted  within  that  of  the  parent 
bird. 

The  proventriculus — an  enlargement  just  above  the  gizzard 
— is  relatively  to  the  latter  very  thin- walled,  but  provides  the 
true  gastric  juices. 

Certain  plants  digest  proteid  matter,  like  animals ;  thus  the 
sun-dew  (Drosera),  by  the  closure  of  its  leaves,  captures  insects, 
which  are  digested  and  the  products  absorbed.  The  digestive 
fluid  consists  of  a  pepsin-containing  secretion,  together  with 
formic  acid. 

The  Digestive  Juices, 

Saliva. — The  saliva  as  found  in  the  mouth  is  a  mixture  of 
the  secretion  of  three  pairs  of  glands,  alkaline  in  reaction,  of  a 
specific  gravity  of  1002  to  1006,  with  a  small  percentage  of 
solids  ('2  per  cent),  consisting  of  salts  and  organic  bodies 
(mucin,  proteids). 

Saliva  serves  mechanical  functions  in  articulation,  in  moist- 
ening the  food,  and  dissolving  out  some  of  its  salts.  But  its 
principal  use  in  digestion  is  in  reducing  starchy  matters  to  a 
soluble  form,  as  sugar.  So  far  as  known,  the  other  constituents 
of  the  food  are  not  changed  chemically  in  the  mouth. 

The  Amylolytic  Action  of  Saliva. — Starch  exists  in  grains,  sur- 
rounded by  a  cellulose  covering,  which  saliva  does  not  digest ; 
hence  its  action  on  raw  starch  is  slow. 

It  is  found  that  if  a  specimen  of  boiled  starch  not  too  thick 
be  exposed  to  a  small  quantity  of  saliva  at  the  temperature  of 
the  body  or  thereabout  (37°  to  40°  C),  it  will  speedily  undergo 
certain  changes : 

1.  After  a  very  short  time  sugar  may  be  detected  by  Feh- 


DIGESTION   OP   FOOD.  3OY 

ling's  solution  (copper  sulphate  in  an  excess  of  sodium  hydrate, 
the  sugar  reducing  the  cupric  hydrate  to  cuprous  oxide  on 
boiling). 

2.  At  this  early  stage  starch  may  still  be  detected  by  the 
blue  color  it  gives  with  iodine ;  but  later,  instead  of  a  blue,  a 
purple  or  red  may  appear,  indicating  the  presence  of  dextrin, 
"svhich  may  be  regarded  as  a  product  intermediate  between 
starch  and  sugar. 

3.  The  longer  the  process  continues,  the  more  sugar  and  the 
less  starch  or  dextrin  to  be  detected;  but,  inasmuch  as  the 
quantity  of  sugar  at  the  end  of  the  process  does  not  exactly 
correspond  with  the  original  quantity  of  starch,  even  when  no 
starch  or  dextrin  is  to  be  found,  it  is  believed  that  other  bodies 
are  formed.  One  of  these  is  achroodextrin,  which  does  not  give 
a  color  reaction  with  iodine. 

The  sugars  formed  are :  (a)  Dextrose.  (5)  Maltose,  which 
has  less  reducing  power  over  solutions  of  copper  salts,  a  more 
jDronounced  rotatory  action  on  light,  etc. 

It  is  found  that  the  digestive  action  of  saliva,  as  in  the 
above-described  experiment,  will  be  retarded  or  arrested  if  the 
sugar  is  allowed  to  accumulate  in  large  quantity.  That  diges- 
tion in  the  mouth  is  substantially  the  same  as  that  just  de- 
scribed can  be  easily  shown  by  holding  a  solution  of  starch  in 
the  mouth  for  a  few  seconds,  and  then  testing  it  for  sugar, 
when  it  will  be  invariably  found. 

While  salivary  digestion  is  not  impossible  in  a  neutral 
medium,  it  is  arrested  in  an  acid  one  even  of  no  great  strength 
(less  than  one  per  cent),  and  goes  on  best  in  a  feebly  alkaline 
medium,  which  is  the  condition  normally  in  the  mouth.  Though 
a  temperature  about  equal  to  that  of  the  body  is  best  adapted 
for  salivary  digestion,  it  will  proceed,  we  have  ourselves  found, 
at  a  higher  temperature  than  digestion  by  any  other  of  the 
juices,  so  far  as  man  is  concerned — a  fact  to  be  connected,  in  all 
probability,  with  his  habit  for  ages  of  taking  very  warm 
fluids  into  the  mouth. 

The  active  principle  of  saliva  is  piyalin,  a  nitrogenous  body 
which  is  assumed  to  exist,  for  it  has  never  been  perfectly  iso- 
lated. It  belongs  to  the  class  of  unorganizccl  fei'iiunits,  the 
properties  of  which  have  been  already  refernMl  to  before  (page 
IGO). 

Characteristics  of  the  Secretion  of  the  Different  Glands. — Parotid 
.saliva  is  in  man  nut  ;i  viscid  lluid,  but  clear  .•uid  limpid,  con- 
taining very  little  mucin.    Submaxillary  saliva  in  most  animals 


308  ANIMAL   PHYSIOLOGY. 

and  in  man  is  viscid,  while  tlie  secretion  of  the  sublingual 
gland  is  still  more  viscid. 

Comparative. — Saliva  differs  greatly  in  activity  in  different 
animals ;  thus  saliva  in  the  dog  is  almost  inert,  that  of  the 
parotid  gland  quite  so ;  in  the  cat  it  is  but  little  more  effective ; 
and  in  the  horse,  ox,  and  sheep,  it  is  known  to  be  of  very  feeble 
digestive  power. 

In  man,  the  Guinea-pig,  the  rat,  the  hog,  both  parotid  and 
submaxillary  saliva  are  active;  while  in  the  rabbit  the  sub- 
maxillary saliva,  the  reverse  of  the  preceding,  is  almost  in- 
active, and  the  parotid  secretion  very  powerful. 

An  aqueous  or  glycerine  extract  of  the  salivary  glands  has 
digestive  properties.  The  secretion  of  the  different  glands 
may  be  collected  by  passing  tubes  or  cannulas  into  their  ducts. 

Pathological. — Potassium  sulphocyanate  (which  gives  a  red 
color  with  salts  of  iron)  is  sometimes  present  normally,  but  is 
said  to  be  in  excess  in  certain  diseases,  as  rheumatism. 

The  saliva,  normally  neutral  or  only  faintly  acid,  may  be- 
come very  much  so  in  the  intervals  of  digestion  The  rapid 
decay  of  the  teeth  occurring  during  and  after  pregnancy 
seems  in  certain  cases  to  be  referable  in  part  to  an  abnormal 
condition  of  the  saliva,  and  in  part  to  the  drain  on  the  lime 
salts  in  the  construction  of  the  bones  of  the  foetus. 

The  tartar  which  collects  on  the  teeth  consists  largely  of 
earthy  phosphates. 

Gastric  Juice. — Gastric  juice  may  be  obtained  from  a  fistu- 
lous opening  into  the  stomach.  Such  may  be  made  artificially 
by  an  incision  over  the  organ  in  the  middle  line,  catching  it  up 
and  stitching  it  to  the  edges  of  the  wound,  incising  and  insert- 
ing a  special  form  of  cannula,  which  may  be  closed  or  opened 
at  will. 

Digestion  in  a  few  cases  of  accidental  gastric  fistulse  has 
been  made  the  subject  of  careful  study.  The  most  instructive 
case  is  that  of  Alexis  St.  Martin,  a  French  Canadian,  into 
whose  stomach  a  considerable  opening  was  made  by  a  gunshot- 
wound. 

Gastric  juice  in  his  case  and  in  the  lower  animals  with  arti- 
ficial openings  in  the  stomach,  has  been  obtained  by  irritating 
the  mucous  lining  mechanically  with  a  foreign  body,  as  a  feather. 

The  great  difficulty  in  all  such  cases  arises  from  the  impos- 
sibility of  being  certain  that  such  fluid  is  normal ;  for  the  con- 
ditions which  call  forth  secretion  are  certainly  such  as  the 
stomach  never  experiences  in  the  ordinary  course  of  events. 


DIGESTION  OF   FOOD. 


309 


and  ■sve  liave  seen  how  saliva  varies,  according  as  the  animal  is 
fasting  or  feeding,  etc. 

Bearing  in  mind,  then,  that  onr  knowledge  is  possibly  only 
approximately  correct,  we  may  state  what  is  known  of  the  se- 
cretions of  the  stomach. 

The  gastric  secretion  is  clear,  colorless,  of  low  specific  grav- 
ity (1001  to  1010)^  the  solids  being  in  great  part  made  up  of  pep- 


FiG.  267.— Gastric  fistula  in  case  of  St.  Martin  (after  Beaumont).  A,  A,  A,  B,  borders  of  open- 
ing into  stoniacVi  ;  C,  left  nipple  :  D.  chest :  E,  cicatrices  from  wound  made  for  removal 
of  a  piece  of  cartilage  ;  F,  F,  F,  cicatrices  of  original  wound. 

sin  with  a  small  quantity  of  mucus,  which  may  become  excess- 
ive in  disordered  conditions.  There  has  been  a  good  deal  of 
dispute  as  to  the  acid  found  in  the  stomach  during  digestion. 
It  is  now  generally  agreed  that  during  the  greater  part  of  the 
digestive  jjrocess  there  is  free  hydrochloric  acid  to  the  extent 
of  about  '2  per  cent.  It  is  maintained  that  lactic  acid  exists 
normally  in  the  early  stages  of  digestion,  and  it  is  conceded 
that  lactic,  butyric,  acetic,  and  other  acids  may  be  present  in 
certain  forms  of  disordered  digestion. 

It  is  also  generally  acknowledged  that  in  mammals  the 
work  of  the  stomach  is  limited,  so  far  as  actual  chemical 
clianges  go,  to  the  conversion  of  the  proteid  constituents  of 
food  into  xjeptone.  Fats  may  be  released  from  their  proteid 
coverings  (cells),  but  neither  they  nor  starches  are  in  the  least 
altererl  chemically.  Some  have  thought  that  in  the  dog  ilievv. 
i.s  a  slit^ht    digestion   of   fats   in   the   stomach.     The   solvent 


310  ANIMAL  PHYSIOLOGY. 

power  of  the  gastric  juice  is  greater  than  can  be  accounted 
for  by  the  presence  of  the  acid  it  contains  merely,  and  it  has 
a  marked  antiseptic  action. 

Digestive  processes  may  be  conducted  out  of  the  body  in  a 
very  simple  manner,  which  the  student  may  carry  out  for 
himself.  To  illustrate  by  the  case  of  gastric  digestion:  The 
mucous  membrane  is  to  be  removed  from  a  pig's  stomach 
after  its  surface  has  been  washed  clean,  but  not  too  thoroughly^, 
chopped  up  fine,  and  divided  into  two  parts.  On  one  half  pour 
water  that  shall  contain  "2  per  cent  hydrochloric  acid  (made 
by  adding  4  to  6  cc.  commercial  acid  to  1,000  cc.  water).  This 
will  extract  the  pepsin,  and  may  be  used  as  the  menstruum  in 
which  the  substance  to  be  digested  is  placed.  The  best  is  fresh 
fibrin  whipped  from  blood  recently  shed. 

Since  the  fluid  thus  prepared  will  contain  traces  of  peptone 
from  the  digestion  of  the  mucous  membrane,  it  is  in  some 
respects  better  to  use  a  glycerine  extract  of  the  same.  This  is 
made  by  adding  some  of  the  best  glycerine  to  the  chopped-up 
mucous  membrane  of  the  stomach  of  a  pig,  etc.,  well  dried  with 
bibulous  paper,  letting  the  whole  stand  for  eight  to  ten  days, 
filtering  through  cotton,  and  then  through  coarse  filter-paper. 
It  will  be  nearly  colorless,  clear,  and  powerful,  a  few  drops  suf- 
ficing for  the  work  of  digesting  a  little  fibrin  when  added  to 
some  two  per  cent  hydrochloric  acid. 

Digestion  goes  on  best  at  about  40°  C,  but  will  proceed  in 
the  cold  if  the  tube  in  which  the  materials  have  been  placed  is 
frequently  shaken.  It  is  best  to  place  the  test-tube  containing 
them  in  a  beaker  of  water  kept  at  about  blood-heat.  Soon  the 
fibrin  begins  to  swell  and  also  to  melt  away. 

After  fifteen  to  twenty  minutes,  if  a  little  of  the  fluid  in  the 
tube  be  removed  and  filtered,  and  to  the  filtrate  added  carefully 
to  neutralization  dilute  alkali,  a  precipitate,  insoluble  in  water 
but  soluble  in  excess  of  alkali  (or  acid),  is  thrown  down.  This 
is  in  most  respects  like  acid-albumen,  but  has  been  called  para- 
peptone.  The  longer  digestion  proceeds,  the  less  is  there  of 
this  and  the  more  of  another  substance,  peptone,  so  that  the 
former  is  to  be  regarded  as  an  intermediate  product.  Peptone 
is  distinguished  from  albuminous  bodies  or  proteids  by — 1. 
Not  being  coagulable  from  its  aqueous  solutions  on  boiling. 
2.  Diffusing  more  readily  through  animal  membranes.  3.  Not 
being  precipitated  by  a  number  of  reagents  that  usually  act 
on  proteids. 

In  artificial  digestion  it  is  noticeable  that  much  more  fibrin 


DIGESTION   OP   FOOD.  3U 

or  other  proteid  matter  will  be  dissolved  if  it  be  finely  divided 
and  frequently  shaken  up,  so  that  a  greater  surface  is  exposed 
to  the  digestive  fluid. 

The  exact  nature  of  the  process  by  which  proteid  is  changed 
to  peptone  is  not  certainly  known. 

Since  starch  on  the  addition  of  water  becomes  sugar  (CeHjo 
Os  +  HgO  =  CeHisOe),  and  since  jjeptones  have  been  formed 
through  the  action  of  dilute  acid  at  a  high  temperature  or  by 
superheated  water  alone,  it  is  possible  that  the  digestion  of 
both  starch  and  proteids  may  be  a  hydration  ;  but  we  do  not 
know  that  it  is  such. 

As  already  explained,  milk  is  curdled  by  an  extract  of  the 
stomach  (rennet)  ;  and  this  can  take  place  in  the  absence  of  all 
acids  or  anything  else  that  might  be  suspected  except  the  real 
cause ;  there  seems  to  be  no  doubt  that  there  is  a  distinct  fer- 
ment which  produces  the  coagulation  of  milk  which  results 
from  the  precipitation  of  its  casein. 

The  activity  of  the  gastric  juice,  and  all  extracts  of  the  mu- 
cous membrane  of  the  stomach,  on  proteids,  is  due  to  pepsin,  a 
nitrogenous  body,  but  not  a  proteid. 

Like  other  ferments,  the  conditions  under  which  it  is  effect- 
ive are  well  defined.  It  will  not  act  in  an  alkaline  medium  at 
all,  and  if  kept  long  in  such  it  is  destroyed.  In  a  neutral  me- 
dium its  power  is  suspended  but  not  destroyed.  Digestion  will 
go  on,  though  less  perfectly,  in  the  presence  of  certain  other 
acids  than  hydrochloric.  As  with  all  digestive  ferments,  the 
activity  of  pepsin  is  wholly  destroyed  by  boiling. 

When  a  large  quantity  of  cane-sugar  is  taken  into  the 
stomach,  an  excess  of  mucus  is  poured  out  which  converts  it, 
presumably  by  means  of  a  special  ferment,  into  dextrose. 

Bile. — The  composition  of  human  bile  is  stated  in  the  fol- 
lowing table : 

Water 82-90  per  cent. 

Bile-salts G-11     "     ." 

Fats  and  soaps 3         "      " 

Cholesterin 0-4      "      " 

Lecithin rs      "      " 

Mucin 1-3      "      " 

Ash 0-Gl     "      " 

The  color  of  tlie  bile  of  man  is  a  rich  gold(;n  yellow.  When 
it  contains  much  mucus,  as  is  the  case  Avhen  it  remains  long  in 
the  gall-bladder,  it  is  ropy,  though  usually  clear.  Bile  may 
contain  small  fjuantiti(;s  of  iivjii,  manganese,  and  cop])er,  the 


312  ANIMAL  PHYSIOLOGY. 

latter  two  especially  being  absent  from  all  other  fluids  of  the 
body.  Sodium  chloride  is  the  most  abundant  salt.  Bile  must 
be  regarded  as  an  excretion  as  well  as  a  secretion ;  the  pig- 
ments, copper,  manganese,  and  perhaps  the  iron  and  the  cho- 
lesterin  being  of  little  or  no  use  in  the  digestive  processes,  so 
far  as  known. 

The  hile-salts  are  the  essential  constituents  of  bile  as  a 
digestive  fl.uid.  In  man  and  many  other  animals,  they  con- 
sist of  taurocholate  and  glycocholate  of  sodium,  and  may  be 
obtained  in  bundles  of  needle-shaped  crystals  radiating  from 
a  common  center.  These  salts  are  soluble  in  water  and  alco- 
hol, with  an  alkaline  reaction,  but  insoluble  in  ether. 

Glycocholic  acid,  may  be  resolved  into  cholalic  (cholic)  acid 
and  glycin  (glycocoll) ;  and  taurocholic  acid  into  cholalic  acid 
and  taurin.     Thus : 

Glycocholic  acid.  Cliolalic  acid.  Glycin. 

C26H43NO6  +  H2O  =  C24H40O5  +  C2H5NO2. 
Taurocholic  acid.  Cholalic  acid.  Taurin. 

C26H45NSO7  +  H20  =  C24H40O5  +  CaH.NSOs. 
Glycocoll  (glycin)  is  amido-acetic  acid — 

CO2H' 
Taurin,  amido-isethionic  acid. 


CH2<t:„  „,  and 


SO  H 
C2H4<,.Ji?.    ,  and  may  be  made  artificially 

NH2 

from  isethionic  acid. 

It  is  to  be  noted  that  the  bile  acids  both  contain  nitrogen, 
but  that  chololic  acid  does  not.  The  decomposition  of  the  bile 
acids  takes  place  in  the  alimentary  canal,  and  the  glycin  and 
taurin  are  restored  to  the  blood,  and  are  possibly  used  afresh 
in  the  construction  of  the  bile  acids,  though  this  is  not  defi- 
nitely known. 

Bile-Pigments. — The  yellowish-red  color  of  the  bile  is  owing 
to  Bilirubin  (CisHisNsOs),  which  may  be  separated  either  as 
an  amorphous  yellow  powder  or  in  tablets  and  prisms.  It  is 
soluble  in  chloroform,  insoluble  in  water,  and  but  partially 
soluble  in  alcohol  and  ether.  It  makes  up  a  large  part  of 
gall-stones,  which  contain,  besides  cholesterin,  earthy  salts  in 
abundance. 

It  may  be  oxidized  to  Biliverdin  (Ci6H,8N204),  the  natural 
green  pigment  of  the  bile  of  the  herbivora.  When  a  drop  of 
nitric  acid,  containing  nitrous  acid,  is  added  to  bile,  it  under- 


DIGESTION   OF   FOOD.  313 

goes  a  series  of  color  changes  in  a  certain  tolerably  constant 
order,  becoming  green,  greenish-blue,  blue,  violet,  a  brick  red, 
and  finally  yellow ;  though  the  green  is  the  most  characteristic 
and  permanent.  Each  one  of  these  represents  a  distinct  stage 
of  the  oxidation  of  bilirubin,  the  green  answering  to  biliverdin. 
Such  is  Gmelin's  test  for  bile-pigments,  by  which  they  may  be 
detected  in  urine  or  other  fluids.  The  absence  of  proteids  in 
bile  is  to  be  noted. 

The  Digestive  Action  of  Bile.— 1.  So  far  as  known,  its  action 
on  proteids  is  }iil.  When  bile  is  added  to  the  products  of  an 
artificial  gastric  digestion,  bile-salts,  peptone,  pepsin,  and  para- 
peptone  are  precipitated  and  redissolved  by  excess.  2.  It  is 
slightly  solvent  of  fats,  though  an  emulsion  made  with  bile  is 
very  feeble.  But  it  is  likely  helpful  to  pancreatic  juice,  or 
more  efficient  itself  when  the  latter  is  present.  With  free  fatty 
acids  it  forms  soaps,  which  themselves  help  in  emulsifying  fat. 
3.  Membranes  wet  with  bile  allow  fats  to  pass  more  readily ; 
hence  it  is  inferred  that  bile  assists  in  absorption.  4.  When 
bile  is  not  poured  out  into  the  alimentary  canal  the  faeces 
become  clay-colored  and  ill-smelling,  foul  gases  being  secreted 
in  abundance,  so  that  it  would  seem  that  bile  exercises  an  anti- 
septic influence.  It  may  limit  the  quantity  of  indol  formed. 
It  is  to  be  understood  that  these  various  properties  of  bile  are 
to  be  traced  almost  entirely  to  its  salts ;  though  its  alkaline 
reaction  is  favorable  to  digestion  in  the  intestines,  apart  from 
its  helpfulness  in  soap-forming,  etc.  5.  It  is  thought  by  some 
that  the  bile  acts  as  a  stimulant  to  the  intestinal  tract,  giving 
rise  to  jjeristaltic  movements,  and  also,  mechanically,  as  a  lubri- 
cant of  the  faeces.  In  the  opinion  of  many,  an  excess  of  bile 
naturally  poured  out  causes  diarrhoea,  and  it  is  well  known 
that  Ijile  given  by  the  mouth  acts  as  a  purgative.  However, 
we  must  distinguish  between  the  action  of  an  excess  and  that 
of  the  quantity  secreted  by  a  healthy  individual.  The  acid  of 
the  stomach  has  probably  no  effect  allied  to  that  produced  by 
giving  acids  medicinally,  which  warns  us  that  too  much  must 
not  be  made  out  of  the  argument  from  bilious  diarrhoea.  G.  As 
before  intimated,  a  great  part  of  the  bile  must  be  regarded  as 
excrementitious.  It  looks  as  though  much  of  the  effete  haemo- 
globin of  the  blood  and  of  the  cholesterin,  which  represents 
[)0ssibly  some  of  the  waste  of  nervous  metabolism,  were  expelled 
from  the  body  by  the  bile.  Tlie  cholalic  acid  of  the  faeces  is 
derived  from  the  decomposition  of  the  bile  acids.  Part  of  their 
mucus  must  also  be  referred  to  the  bile,  the  quantity  originally 


314 


ANIMAL  PHYSIOLOGY. 


present  in  this  fluid  depending  much,  on  the  length  of  its  stay 
in  the  gall-bladder,  which  secretes  this  substance.  7.  There  is 
throughout  the  entire  alimentary  tract  a  secretion  of  mucus 
which  must  altogether  amount  to  a  large  quantity,  and  it  has 
,been  suggested  that  this  has  other  than  lubricating  or  such  like 
functions.  It  appears  that  mucus  may  be  resolved  into  a  pro- 
teid  and  an  animal  gum,  which  latter^  it  is  maintained,  like 
vegetable  gums,  assists  emulsification  of  fats.  If  this  be  true^ 
and  the  bile  is,  as  has  been  asserted,  possessed  of  the  power  to 
break  up  this  mucus  (mucin),  its  emulsifying  effect  in  the  in- 
testine may  indirectly  be  considerable.  Bile  certainly  seems 
to  intensify  the  emulsifying  power  of  the  pancreatic  juice. 

There  does  not  seem  to  be  any  ferment  in  bile,  unless  the 
power  to  change  starch  into  sugar,  peculiar  to  this  secretion  in 
some  animals,  is  owing  to  such. 

Comparative.— The  bile  of  the  carnivora  and  omnivora  is 
yellowish-red  in  color ;  that  of  herbivora  green.  The  former 
contains  taurocholate  salts  almost  exclusively ;  in  herbivorous 
animals  and  man  there  is  a  mixture  of  the  salts  of  both  acids, 
though  the  glycocholate  predominates. 


Fig.  268.— Gall-bladder,  ductus  choledochus  and  pancreas  (after  Le  Bon),  a,  gall-bladder; 
6,  hepatic  duct ;  c,  opening  of  second  duct  Of  pancreas  ;  d,  opening  of  main  pancreatic 
duct  and  bile-duct ;  e,  e,  duodenum  ;  /,  ductus  choledochus  ;  p,  pancreas. 


Pancreatic  Juice. — This  fluid  is  found  to  vary  a  good  deal 
quantitatively,  according  as  it  is  obtained  from  a  temporary 
(freshly  made)  or  permanent  fistula — a  fact  which  emphasizes 


DIGESTION   OF   FOOD. 


315 


the  necessity  for  caution  in  drawing  conclusions  about  the 
digestive  juices  as  obtained  by  our  present  methods. 

The  freshest  juice  obtainable  through  a  recent  fistulous 
opening  in  the  pancreatic  duct  is  clear,  colorless,  viscid,  alka- 
line in  reaction,  and  with  a  very  variable  quantity  of  solids 
(two  to  ten  per  cent),  less  than  one  per  cent  being  inorganic 
matter. 

Among  the  organic  constituents  the  principal  are  albumin, 
alkali-albumin,  peptone,  leucin,  tyrosin,  fats,  and  soaps  in  small 
amount.    The  alkalinity  of  the  juice  is  owing  chiefly  to  sodium 


Fig.  269.— Crystals?  of  leucin  (Funke). 


Ftg.  270.— Crystals  of  tyrosin  (Funke). 


carbonates,  which  seem  to  be  associated  with  some  proteid 
body.  There  is  little  doubt  that  leucin,  tyrosin,  and  peptone 
arise  from  digestion  of  the  proteids  of  the  juice  by  its  own 
action. 

Experimental— If  the  pancreatic  gland  be  mostly  freed  from 
adhering  fat,  cut  up,  and  washed  so  as  to  get  rid  of  blood ; 
then  minced  as  fine  as  possible,  and  allowed  to  stand  in  one-per- 
cent sodium-carbonate  solution  at  a  temperature  of  40°  C,  the 
following  results  may  be  noted :  1.  After  a  variable  time  the 
reaction  may  change  to  acid,  owing  to  free  fatty  acid  from 
the  decrjmposition  (digestion)  of  neutral  fats.  2.  Alkali-albu- 
min, or  a  b(;dy  closely  resembling  it,  may  be  detected  and  sep- 
arat<'d  by  neutralization.  3.  Prq)fone  may  be  detected  by  the 
use  of  a  trace  of  copper  sulphate  added  to  a  few  drops  of  caustic 
alkali,  which  becomes  red  if  this  body  be  present.  4.  After  a 
fftw  hours  the  smell  becomes  fa?cal,  owing  in  part  to  indol, 
which  gives  a  violet  color  with  chlorine-water;  while  under 
the  microscope  the  digesting  mass  may  be  seen  to  bo  swarming 


316  "  ANIMAL  PHYSIOLOGY. 

with  bacteria.  5.  When  digestion  has  proceeded  for  some  time, 
leucin  and  tyrosin  may  be  shown  to  be  present,  though  their 
satisfactory  separation  in  crystalline  form  involves  somewhat 
elaborate  details.  These  changes  are  owing  to  self-digestion 
of  the  gland. 

All  the  properties  of  this  secretion  may  be  demonstrated 
more  satisfactorily  by  making  an  aqueous  or,  better,  glycerine 
extract  of  the  pancreas  of  an  ox,  pig,  etc.,  and  carrying  on  arti- 
ficial digestion,  as  in  the  case  of  a  peptic  digestion,  with  fibrin. 
In  the  case  of  the  digestion  of  fat,  the  emulsifying  power  of  a 
watery  extract  of  the  gland  may  be  shown  by  shaking  up  a 
little  melted  hog's  lard,  olive-oil  (each  quite  fresh,  so  as  to  show 
no  acid  reaction),  or  soap.  Kept  under  proper  conditions,  free 
acid,  the  result  of  decomposition  of  the  neutral  fats  or  soap 
into  free  acid,  etc.,  may  be  easily  shown.  The  emulsion,  though 
allowed  to  stand  long,  persists,  a  fact  which  is  availed  of  to 
produce  more  palatable  and  easily  assimilated  preparations  of 
cod-liver  oil,  etc.,  for  medicinal  use. 

Starch  is  also  converted  into  sugar  with  great  ease.  In 
short,  the  digestive  juice  of  the  pancreas  is  the  most  complex 
and  complete  in  its  action  of  the  whole  series.  It  is  amylolytic, 
proteolytic,  and  steaptic,  and  these  powers  have  been  attributed 
to  three  distinct  ferments — amylopsin,  trypsin,  and  steapsin. 

Proteid  digestion  is  carried  further  than  by  the  gastric  juice, 
and  the  quantity  of  crystalline  nitrogenous  products  formed  is 
in  inverse  proportion  to  the  amount  of  peptone,  from  which  it 
seems  just  to  infer  that  part  of  the  original  peptone  has  been 
converted  into  these  bodies,  which  are  found  to  be  abundant  or 
not  in  an  artificial  digestion,  according  to  the  length  of  time 
it  has  lasted — the  longer  it  has  been  under  way  the  more  leucin 
and  tyrosin  present.  Leucin  is  another  compound  into  which 
the  amido  (NHj)  group  enters  to  make  amido-caproic  acid — one 
of  the  fatty  series — while  tyrosin  is  a  very  complex  member  of 
the  aromatic  series  of  compounds.  Thus  complicated  are  the 
chemical  effects  of  the  digestive  juices;  and  it  seems  highly 
probable  that  these  are  only  some  of  the  compounds  into 
which  the  proteid  is  broken  up. 

These  crystalline  bodies  may  be  made  artificially  by  the 
long-continued  action  under  heat  of  acids  and  alkalies,  in  pro- 
teid or  gelatinous  matter,  though  it  can  not  be  said  that  these 
facts  have  as  yet  thrown  much  light  upon  their  formation  in 
the  digestive  organs. 

Though  putrefactive  changes  with  formation  of  indol,  etc., 


DIGESTION  OP  FOOD.  317 

occur  in  pancreatic  digestion,  both  within  and  without  the 
body,  they  are  to  be  regarded  as  accidental,  for  by  proper  pre- 
cautions digestion  may  be  carried  on  in  the  laboratory  without 
their  occurrence,  and  they  vary  in  degree  with  the  animal,  the 
individual,  the  food,  and  other  conditions.     It  is  not,  however. 


s 


\fw\  -"^^       ^^^P-       ^^^     ""•<-  \\l\\fo 


Fig.  271.— Micro-orp:anisms  of  large  intestine  (after  LandoisK  1,  bacterium  coli  cummune  ; 
2,  bacterium  lactis  aerogenes  ;  3,  4,  large  bacilli  of  Bienstock,  with  partial  endogenous 
spore-formation  ;  5,  various  stages  of  development  of  bacillus  which  causes  fermentation 
of  albumen. 

to  be  inferred  that  micro-organisms  serve  no  useful  jDurpose 
in  the  alimentary  canal ;  the  subject,  in  fact,  requires  further 
investigation. 

Succus  Entericus. — The  difficulties  of  collecting  the  secretions 
of  Lieberkiihn's,  Briinner's,  and  other  intestinal  glands  will  be 
at  once  apparent.  But  by  dividing  the  intestine  in  two  places, 
so  as  to  isolate  a  loop  of  the  gut,  joining  the  sundered  ends  by 
ligatures,  thus  making  the  continuity  of  the  main  gut  as  com- 
plete as  before,  closing  one  end  of  the  isolated  loop,  and  bring- 
ing the  other  to  the  exterior,  as  a  fistulous  opening,  the  secre- 
tions could  be  collected,  food  introduced,  etc. 

But  it  seems  highly  improbable  that  information  approxi- 
mately correct  at  best,  and  possibly  highly  misleading,  could 
be  obtained  in  such  manner.  Moreover,  the  greatest  diversity 
of  opinion  prevails  as  to  the  facts  themselves,  so  that  it  seems 
scarcely  worth  while  to  state  the  contradictory  conclusions 
arrived  at. 

It  is,  however,  on  the  face  of  it,  probable  that  the  intestine 
— even  the  large  intestine — does  secrete  juices,  that  in  herbiv- 
ora,  at  all  events,  play  no  unimportant  part  in  the  digestion 
of  their  bulky  food;  and  it  is  also  probable,  as  in  so  many 
other  instances,  that,  when  the  other  parts  of  the  digestive 
tract  fail,  when  the  usual  secretions  are  not  prepared  or  do  not 
act  on  the  food,  glands  that  normally  play  a  possibly  insig- 
nificant part  may  function  excessively — we  may  almost  say 
vicariou.sly — and  that  sucli  glands  must  be  sought  in  tin;  small 
intestine.     There  are  facts  in  clinical  medicine  that  seem  to 


318 


ANIMAL   PHYSIOLOGY, 


Fig.  2?'2.— General  vievr  of  horse's  intestines ;  animal  is  placed  on  its  back,  and  intestinal 
mass  spread  out  (after  Chauveau).  A,  duodenum  as  it  passes  behind  great  mesenteric 
artery  ;  B,  free  portion  of  small  intestine  :  C,  ileocaecal  portion  ;  O,  ceecum  \  E  F,  G 
loop  formed  by  large  colon  ;  O,  pelvic  flexure  ;  F,  F,  point  where  colic  loop  is  doubled  to 
constitute  suprasternal  and  diaphragmatic  flexures. 


DIGESTION  OF  FOOD.  319 

point  strongly  in  this  direction,  though  the  subject  has  not  yet 
been  reduced  to  scientific  form. 

Comparative. — Within  the  last  few  years  the  study  of  vege- 
table assimilation  from  the  comparative  aspect  has  been  fruit- 
ful in  results  which,  together  with  many  other  facts  of  vege- 
table metabolism,  show  that  even  plants  ranking  high  in  the 
organic  plane  are  not  in  many  of  their  functions  so  different 
from  animals  as  Ijas  been  supposed.  It  has  been  known  for  a 
longer  period  that  certain  plants  are  carnivorous ;  but  it  was 
somewhat  of  a  surprise  to  find,  as  has  been  done  within  the 
past  few  years,  that  digestive  ferments  are  widely  distributed 
in  the  vegetable  kingdom  and  are  found  in  many  different 
parts  of  plants.  What  purpose  they  may  serve  in  the  vege- 
table economy  is  as  yet  not  well  known.  At  present  it  would 
seem  as  though,  from  their  presence  in  so  many  cases  in  the 
seed,  they  might  have  something  to  do  with  changing  the 
cruder  forms  of  nutriment  into  such  as  are  better  adapted  for 
the  nourishment  of  the  embryo. 

Thus  far,  then,  not  only  diastase  but  pepsin,  a  body  with 
action  similar  to  trypsin,  and  a  rennet  ferment,  rank  among 
the  vegetable  ferments  best  known. 

A  ferment  has  been  extracted  from  the  stem,  leaves,  and  un- 
ripe fruit  of  Carica  papaya,  toxind  in  the  East  and  West  Indies 
and  elsewhere,  which  has  a  marked  proteolytic  action. 

It  is  effective  in  a  neutral,  most  so  in  an  alkaline  medium ; 
and,  though  its  action  is  suspended  in  a  feeble  acid  menstruum, 
it  does  not  appear  to  be  destroyed  under  such  circumstances,  as 
is  trypsin.  This  body  is  attracting  a  good  deal  of  attention, 
and  its  use  has  been  recently  introduced  into  medical  practice. 

Very  lately  also  a  vegetable  rennet  has  been  found  in  sev- 
eral species  of  plants.  The  subject  is  highly  promising  and 
suggestive. 

Secretion  as  a  Physiological  Process. 

Secretion  of  the  Salivary  Glands. — We  sliall  treat  this  subject 
at  more  length  because  of  the  light  it  throws  on  the  nervous 
phenomena  of  vital  proces's ;  and,  since  th(^  salivary  glands  have 
been  studied  more  thoroughly  and  successfully  than  any  other, 
ihey  will  receive  greater  attention. 

The  main  facts,  ascertained  experimentally  and  otherwise, 
are  the  ff^llowing : 

Assuming  that  the  student  is  familiar  with  the  general  ana- 


320 


ANIMAL  PHYSIOLOGY. 


tomical  relations  of  the  salivary  glands  in  some  mammal,  we 
would  further  remind  him  that  the  submaxillary  gland  has  a 
double  nervous  supply :  1.  From  the  cervical  sympathetic  by 
branches  passing  to  the  gland  along  its  arteries.  2.  From  the 
chorda  tympani  nerve,  which  after  leaving  the  facial  makes 
connection  with  the  lingual,  whence  it  proceeds  to  its  destina- 
tion. 


Part  of  brain  above  medulla 


Afferent  nerves 
from  tongue ' 


■Salivary  gland 


Blood  vessel 
of  gland 


'Superior  cerv.  ganglion 


Sympathetic  nerve 


Fig.  273.— Diagram  intended  to  indicate  the  nervous  mechanism  of  salivary  secretion. 


The  following  facts  are  of  importance  as  a  basis  for  conclu- 
sions :  1.  It  is  a  matter  of  common  observation  that  a  flow  of 
saliva  may  be  excited  by  the  smell,  taste,  sight,  or  even  thought 
of  food.  2.  It  is  also  a  matter  of  experience  that  emotions,  as 
fear,  anxiety,  etc.,  may  parch  the  mouth — i.  e.,  arrest  the  flow  of 
saliva.     The  excited  speaker  thus  suffers  in  his  early  efforts. 


DIGESTION  OF   FOOD.  321 

3,  If  a  glass  tube  be  placed  in  tlie  duct  of  the  gland  and  any 
substance  that  naturally  causes  a  flow  of  saliva  be  placed  on 
the  tongue,  saliva  may  be  seen  to  rise  rapidly  in  the  tube.  4. 
The  same  may  be  observed  if  the  lingual  nerve,  the  glossopha- 
ryngeal, and  many  other  nerves  be  stimulated ;  also  if  'food  be 
introduced  into  the  stomach  through  a  fistula.  5.  If  the  pe- 
ripheral end  of  the  chorda  tympani  be  stimulated,  two  results 
follow :  (a)  There  is  an  abundant  flow  of  saliva,  and  (6)  the 
arterioles  of  the  gland  become  dilated ;  the  blood  may  pass 
through  with  such  rapidity  that  the  venous  blood  may  be 
bright  red  in  color  and  there  may  be  a  venous  pulse.  7.  Stimu- 
lation of  the  medulla  oblongata  gives  rise  to  a  flow  of  saliva, 
which  is  not  possible  when  the  nerves  of  the  gland,  especially 
the  chorda  tympani,  are  divided ;  nor  can  a  flow  be  then  excited 
by  any  sort  of  nervous  stimulation,  excepting  that  of  the  ter- 
minal branches  of  the  nerves  of  the  gland  itself.  8.  If  the  sym- 
pathetic nerves  of  the  gland  be  divided,  there  is  no  immediate 
flow  of  saliva,  though  there  may  be  some  dilatation  of  its  ves- 
sels. 9.  Stimulation  of  the  terminal  ends  of  the  sympathetic 
and  chorda  nerves  causes  a  flow  of  saliva,  differing  as  to  total 
quantity  and  the  amount  of  contained  solids ;  but  the  nerve 
that  produces  the  more  abundant  watery  secretion,  or  the  re- 
verse, varies  with  the  animal,  e.  g.,  in  the  cat  chorda  saliva  is 
more  viscid,  in  the  dog  less  so  ;  though  in  all  animals  as  yet 
examined  it  seems  that  the  secretion  as  a  result  of  stimulation 
of  the  chorda  tympani  nerve  is  the  more  abundant ;  and  in  the 
case  of  stimulation  of  the  chorda  the  vessels  of  the  gland  are 
dilated,  while  in  the  case  of  the  sympathetic  they  are  con- 
stricted. 10.  If  atropin  be  injected  into  the  blood,  it  is  impos- 
sible to  induce  salivary  secretion  by  any  form  of  stimulation, 
though  excitation  of  the  chorda  nerve  still  causes  arterial  dila- 
tation. 

Conclusions. — 1.  There  is  a  center  in  the  medulla  presiding 
over  salivary  secretion.  2.  The  influence  of  this  center  is 
rendered  eft'ective  through  the  chorda  tympani  nerve  at  all 
events,  if  not  also  by  the  sympathetic.  3.  The  chorda  tym- 
pani nerve  contains  both  secretory  and  vaso-dilator  fibers ;  the 
sympathetic  secretory  and  vaso-constrictor  fibers.  4.  Artcn'ial 
change  is  not  essential  to  secretion,  though  doul)tless  it  usually 
accompanies  it.  Secretion  may  be  induced  in  the  glands  of 
an  animal  after  decapitation  by  stimulation  of  its  chorda 
tympani  nerve,  anah>gous  to  the  secretion  of  sweat  in  tins  foot 
of  ;i  recently  (h^ad  animal,  under  stimulation  of  tlicf  sciatic 
21 


322  ANIMAL   PHYSIOLOGY. 

nerve.  5.  The  character  of  the  saliva  secreted  varies  with 
the  nerve  stimulated,  so  that  it  seems  likely  that  the  nervous 
centers  normally  in  the  intact  animal  regulate  the  quality  of 
the  saliva  through  the  degree  to  which  one  or  the  other  kind 
of  nerves  is  called  into  action.  6.  Secretion  of  saliva  may 
be  induced  reflexly  by  experiment,  and  such  is  probably  the 
normal  course  of  events.  7.  The  action  of  the  medullary  center 
may  be  inhibited  by  the  cerebrum  (emotions). 

Some  have  located  a  center  in  the  cerebral  cortex  (taste  cen- 
ter), to  which  it  is  assumed  impulses  first  travel  from  the 
tongue  and  which  then  rouses  the  proper  secreting  centers  in 
the  medulla  into  activity.  It  seems  more  likely  that  the  corti- 
cal center,  if  there  be  one,  completes  the  physiological  processes 
by  which  taste  sensations  are  elaborated. 

From  the  influence  of  drugs  (atropin  and  its  antagonist 
pilocarpin)  it  is  plain  that  the  gland  can  be  affected  through 
the  blood,  though  whether  wholly  by  direct  action  on  the  cen- 
ter, on  any  local  nervous  mechanism  or  directly  on  the  cells,  is 
as  yet  undetermined.  It  is  found  that  pilocarpin  can  act  long 
after  section  of  the  nerves.  This  does  not,  however,  prove  that 
in  the  intact  animal  such  is  the  usual  modus  operandi  of  this 
or  other  drugs,  any  more  than  the  so-called  paralytic  secretion 
after  the  section  of  nerves  proves  that  the  latter  are  not  con- 
cerned in  secretion. 

We  look  upon  paralytic  secretion  as  the  work  of  the  cells 
when  gone  wrong — passed  from  under  the  dominion  of  the 
nerve-centers.  Secretion  is  a  part  of  the  natural  life-processes 
of  gland-cells — we  may  say  a  series  in  the  long  chain  of  pro- 
cesses which  are  indispensable  for  the  health  of  these  cells. 
They  must  be  either  secreting  cells,  or  have  no  place  in  the  nat- 
ural order  of  things.  It  is  to  be  especially  noted  that  the  secre- 
tion of  saliva  continues  when  the  pressure  in  the  ducts  of  the 
gland  is  greater  than  that  of  the  blood  in  its  vessels  or  even 
of  the  carotid ;  so  that  it  seems  possible  that  over-importance 
has  been  attached  to  blood  -  pressure  in  secretory  processes 
generally. 

It  may,  then,  be  safely  assumed  that  formation  of  saliva  re- 
sults in  consequence  of  the  natural  activity  of  certain  cells,  the 
processes  of  which  are  correlated  and  harmonized  by  the  nerv- 
ous system  ;  their  activity  being  accompanied  by  an  abundant 
supply  of  blood.  The  actual  outpouring  of  saliva  depends  usu- 
ally on  the  establishment  of  a  nervous  reflex  arc.  The  other 
glands  have  been  less  carefully  studied,  but  the  parotid  is 


DIGESTION  OP  FOOD.  323 

known  to  have  a  double  nervous  supply  from  the  cerebro- 
spinal and  the  sympathetic  systems. 

It  would  appear  that,  as  the  vaso-motor  changes  run  paral- 
lel with  the  secretory  ones,  the  vaso-motor  and  the  proper 
secretory  centers  act  in  concert,  as  we  have  seen  holds  of  the 
former  and  the  respiratory  center.  But  it  is  to  our  own  mind 
very  doubtful  whether  the  doctrine  of  so  sharp  a  demarkation 
of  independent  centers,  prominently  recognized  in  the  physi- 
ology of  the  day,  will  be  that  ultimately  accepted. 

Secretion  by  the  Stomach. — The  mucous  membrane  of  St.  Mar- 
tin's stomach  was  observed  to  be  pale  in  the  intervals  of  diges- 
tion, but  flushed  when  secreting,  which  resembled  sweating,  so 
far  as  the  flow  of  the  fluid  is  concerned.  When  the  man  was 
irritated,  the  gastric  membrane  became  pale,  and  secretion  was 
lessened  or  arrested,  and  it  is  a  common  experience  that  emo- 
tions may  help,  hinder,  or  even  render  aberrant  the  digestive 
processes. 

While  the  evidence  is  thus  clear  that  gastric  secretion  is 
regulated  by  the  nervous  system,  the  way  in  which  this  is 
accomplished  is  very  obscure.  We  know  little  of  either  the 
centers  or  nerves  concerned,  and  what  we  do  know  helps  but 
doubtfully  to  an  understanding  of  the  matter,  if,  indeed,  it 
does  not  actually  confuse  and  jDuzzle. 

Digestion  can  proceed  in  a  fashion  after  section  of  the  nerves 
going  to  the  stomach,  though  this  has  little  force  as  an  argu- 
ment against  nerve  influence.  We  may  conclude  the  subject 
by  stating  that,  while  the  influence  of  the  nervous  system  over 
gastric  secretion  is  undoubted  as  a  fact,  the  method  is  not 
understood ;  and  the  same  remark  applies  to  the  secreting 
activity  of  the  Ywcv  and  pancreas. 

The  Secretion  of  Bile  and  Pancreatic  Juice. — When  the  contents 
of  the  stomach  have  reached  the  orifice  of  the  discharging  bile- 
duct,  a  large  flow  of  the  biliary  secretion  takes  place,  probably 
as  the  result  of  the  emptying  of  the  gall-bladder  by  the  con- 
traction of  its  walls  and  those  of  its  ducts.  This  is  probably 
a  reflex  act,  and  the  augmented  flow  of  bile  when  digestiwi  is 
proceeding  is  also  to  be  traced  chiefly  to  nervous  influences 
reaching  the  gland,  though  by  what  nerves  or  under  the  gov- 
ernment of  what  part  of  the  nervous  centers  is  unknown. 
Very  similar  statements  apply  to  the  secretion  of  the  pancre- 
atic glands,  though  this  is  not  constant,  as  in  the  case  of  bile — 
at  all  events,  in  most  animals. 

It  is  known  that  after  food  lias  been  taken  there  is  a  sudden 


324 


ANIMAL   PHYSIOLOGY. 


increase  in  tlie  quantity  of  bile  secreted,  followed  by  a  sudden 
diminution,  then  a  more  gradual  rise,  with  a  subsequent  fall. 
Almost  the  same  holds  for  the  pancreas. 


Fig.  274.— Diagram  to  show  influence  of  food  in  secretion  of  pancreatic  juice  (after  N.  O.  Bern- 
stein). Ttie  abscissae  represent  hours  after  taking  food  ;  ordinates  amount  in  cubic  centi- 
grammes of  secretion  in  ten  minutes.  Food  was  taken  at  B  and  C.  This  diagram  very 
nearly  also  represents  the  secretion  of  bile. 


It  seems  impossible  to  explain  these  facts,  especially  the 
first  rapid  discharge  of  fluid  apart  from  the  direct  influence  of 
the  nervous  system. 

Upon  the  whole,  the  evidence  seems  to  show  that  the  press- 
ure in  the  bile-ducts  is  greater  than  in  the  veins  that  unite  to 
make  up  the  portal  system;  but  there  are  difficulties  in  the 
investigation  of  such  and  kindred  subjects  as  regards  the  liver, 
owing  to  its  peculiar  vascular  supply.  It  will  be  borne  in  mind 
that  the  liver  in  mammals  consists  of  a  mass  of  blood-vessels, 
between  the  meshes  of  which  are  packed  innumerable  cells,  and 
that  around  the  latter  meander  the  bile  capillaries ;  that  the 
portal  vein  breaks  up  into  the  interlobular,  from  which  capil- 
laries arise,  that  terminate  in  the  central  intralobular  veins, 
which  make  up  the  hepatic  veinlets  or  terminate  in  these  vessels 
But  the  structure  is  complicated  by  the  branches  of  the  hepatic 
artery,  which,  as  arterioles  and  capillaries,  enters  to  some  extent 
into  the  formation  of  the  lobular  vessels.  It  is  remarkable  that 
the  cells  of  the  liver  are  so  similar,  considering  the  complicated 
functions  they  appear  to  discharge. 


DIGESTION  OP  FOOD. 


325 


A  question  of  interest,  though  difficult  to  answer,  is  the 
extent  to  which  the  various  constituents  of  bile  are  manufact- 
ured in  the  liver.     Taurin,  for  example,  is  present  in  some  of 


Fig.  275.— Lobules  of  liver,  interlobular  vessels,  and  intralobular  veins  (Sappey).  1, 1, 1, 1,  3, 4, 
lobules  :  2.  2.  2.  2.  intralobular  veins  injected  with  white  ;  5,  5,  5,  5,  5,  intralobular  vessels 
filled  with  a  dark  injection. 


the  tissues,  but  whether  this  is  used  in  the  manufacture  of 
taurocholic  acid  or  whether  the  latter  is  made  entirely  anew, 
and  possibly  by  a  method 
in  which  taurin  never  ap- 
pears as  such,  is  an  open 
question.  It  is  highly  prob- 
able that  a  portion  of  the 
bile  poured  into  the  intes- 
tine is  absorbed  either  as 
such  or  after  i)artial  decom- 
position, the  products  to  be 
used  in  some  way  in  the 
economy  and  presumably  in 
the  construction  of  bile  by 
the  liver.  There  arc  many 
facts,  including  some  patho- 
logical phenomena,  that 
point  clearly  to  the  forma- 
tion of  the  pigments  of  bile 
from  hemoglobin  in  some 
of  its  stages  of  degeneration. 
Pathological. — When  tlic 


Fio  276.— Portion  of  transvei  se  section  of  hepatic 
lobnle  of  rabbit:  inaKnIflfd  4(H)  diam.-ters 
(Koliiker).  I>,  h.  h,  rai)illary  lilood  vessels  ; 
7,  J/,  '/.  capillary  l)ile-du<;ts  ;  /,  Z,  L  liver-cells. 


liver  fails  to  act  either  from  de- 


326  ANIMAL  PHYSIOLOGY. 

rangemeiit  of  its  cells  primarily  or  owing  to  obstruction  to  the 
outflow  of  bile  leading  to  reabsorption  by  the  liver,  bile  acids 
and  bile  pigments  appear  in  the  urine  or  may  stain  the  tissues, 
indicating  their  presence  in  excess  in  the  blood. 

This  action  of  one  gland  (kidneys)  for  another  is  highly 
suggestive,  and  especially  important  to  bear  in  mind  in  medical 
practice,  both  in  treatment  and  prognosis.  The  chances  of  re- 
covery when  only  one  excreting  gland  is  diseased  are  much 
greater  evidently  than  when  several  are  involved.  Such  facts 
as  we  have  cited  show,  moreover,  that  there  are  certain  common 
fundamental  principles  underlying  secretion  everywhere  —  a 
statement  which  will  be  soon  more  fully  illustrated. 

The  Nature  of  the  Act  of  Secretion. 

We  are  now  about  to  consider  some  investigations,  more 
particularly  their  results,  which  are  of  extraordinary  interest. 

The  secreting  cells  of  the  salivary,  the  pancreatic  glands, 
and  the  stomach  have  been  studied  by  a  combination  of  histo- 
logical and,  more  strictly,  physiological  methods,  to  which  we 
shall  now  refer.  Specimens  of  these  glands,  both  before  and 
after  prolonged  secretion,  under  stimulation  of  these  nerves, 
were  hardened,  stained,  and  sections  prepared.  As  was  to  be 
expected,  the  results  were  not  entirely  satisfactory  under  these 
methods ;  however,  the  pancreas  of  a  living  rabbit  has  been 
viewed  with  the  microscope  in  its  natural  condition ;  and  by 
this  plan,  especially  when  supplemented  by  the  more  involved 
and  artificial  method  first  referred  to,  results  have  been  reached 


Fig.  277.— Portion  of  pancreas  of  rabbit  (after  Kiihne  and  Lea).    A  represents  gland  at  rest ; 

B,  during  secretion. 

which  may  be  ranked  among  the  greatest  triumphs  of  modern 
physiology. 


DIGESTION  OP  FOOD.  327 

Some  of  these  we  now  proceed  to  state  briefly.  To  begin 
with  the  pancreas,  it  has  been  shown  that,  when  the  gland  is 
not  secreting — i.  e.,  not  discharging  its  prepared  fluid — or  dur- 
ing the  so-called  resting  stage,  the  appearances  are  strikingly- 
different  from  what  they  are  during  activity.  The  cell  pre- 
sents during  rest  an  inner  granular  zone  and  an  outer  clearer 
zone,  which  stains  more  readily,  and  is  relatively  small  in  size. 
The  lumen  of  the  alveolus  is  almost  obliterated,  and  the  in- 
dividual cells  very  indistinct.  After  a  period  of  secreting 
activity,  the  lumen  is  easily  perceived,  the  granules  have  dis- 
appeared in  great  part,  the  cells  as  a  whole  are  smaller,  and 
have  a  clear  appearance  throughout.  Coincident  with  the 
changes  in  the  gland's  cells  it  is  to  be  noticed  that  more  blood 
passes  through  it,  owing  to  dilatation  of  the  arterioles. 


\\ 


,-n<^ 


B 


Fig.  278.— Section  of  mucous  gland  (after  Lavdowsky).     In  A,  gland  at  rest ;  in  B,  after 

secreting  for  some  time. 

Again,  the  course  of  the  changes  in  the  salivary  glands, 
whether  of  the  mucous  or  serous  variety,  is  very  similar.  In 
the  mucous  gland  in  the  resting  stage  the  cells  are  large,  and 
hold  much  clear  matter  in  the  interspaces  of  the  cell  network ; 
and,  as  this  does  not  stain  readily,  it  can  not  be  ordinary 
protoplasm.  This,  when  the  gland  is  stimulated  through  its 
nerves,  disappears,  leaving  the  containing  cells  smaller.  It 
has  become  mucin,  and  may  itself  be  called  mucinoyen. 

It  is  to  be  noted  that,  as  the  cells  become  more  protoplasmic, 
less  burdened  with  the  products  of  their  activity,  the  nucleus 
becomes  more  prominent,  suggestive  of  its  having  a  probable 
directive  influence  over  these  manufacturing  processes. 

Substantially  the  same  chain  of  events  has  been  established 
for  the  serous  salivary  glands  and  the  stomach,  so  that  we 
may  safely  generalize  upon  these  well-established  facts. 


328 


ANIMAL  PHYSIOLOGY. 


It  seems  clear  that  a  series  of  clianges  constructive  and,  from 
one  point  of  view,  destructive,  following  the  former  are  con- 


FiG.  279.— Changes  in  parotid  (serous)  gland  during  secretion  (after  Langlej').    A,  during  rest ; 
B,  after  moderate,  C,  after  prolonged  stimulation.    Figures  partly  diagrammatic. 


stantly  going  on  in  the  glands  of  the  digestive  organs.  Proto- 
plasm under  nerve  influence  constructs  a  certain  substance, 
which  is  an  antecedent  of  the  final  product,  which  we  term  a 
ferment.  It  is  now  customary  to  speak  of  these  changes  as 
constructive  (anabolic)  and  destructive  (katabolic),  though  we 
have  already  pointed  out  (page  270)  that  this  view  is,  at  best, 
only  one  way  of  looking  at  the  matter,  and  we  doubt  if  it  may. 
not  be  cramping  and  misleading. 

We  must  also  urge  caution  in  regard  to  the  conception  to 
be  associated  with  the  use  of  the  terms  "  resting  "  and  "  active  " 
stage.  It  is  not  to  be  forgotten  that  strictly  in  living  cells 
there  is  no  absolute  rest — such  means  death ;  but,  if  these  terms 
be  understood  as  denoting  but  degrees  of  activity,  they  need 
not  mislead.  It  is  also  more  than  probable  that  in  certain  of 
the  glands,  or  in  some  animals,  the  processes  go  on  simultane- 
ously :  the  protoplasm  being  renewed,  the  zymogen,  or  mother- 
ferment,  being  formed,  and  the  latter  converted  into  actual  fer- 
ment, all  at  the  same  time. 

It  has  been  pointed  out  that  chorda  saliva  is  usually  more 
watery  than  that  secreted  under  stimulation  of  the  sympathetic. 
When  atropine  is  injected  there  is  no  discharge  whatever,  not- 
withstanding that  the  usual  vascular  dilatation  follows,  from 
which  it  is  clear  that  the  water  is  actually  secreted. 

The  nature  of  secretion  is  now  tolerably  clear  as  a  whole ; 
though  it  is  to  be  remembered  that  this  account  is  but  general, 
and  that  there  are  many  minor  differences  for  each  gland  and 
variations  that  can  scarcely  be  denominated  minor  for  different 
animals.  Evidently  no  theory  of  filtration,  no  process  depend- 
ing solely  on  blood-pressure,  will  apply  here.  And  if  in  this, 
the  best-studied  case,  mechanical  theories  of  vital  processes 
utterly  fail,  why  attempt  to  fasten  them  upon  other  glands,  as 


DIGESTION   OF   FOOD.  329 

the  kidneys  and  the  lungs,  or,  indeed,  apply  such  crude  concep- 
tions to  the  subtle  processes  of  living  protoplasm  anywhere  or 
in  any  form  ? 

It  is  somewhat  remarkable  that  an  extract  of  a  perfectly 
fresh  pancreas  is  not  proteolytic ;  yet  the  gland  yields  such  an 
extract  when  it  has  stood  some  hours  or  been  treated  with  a 
weak  acid.  These  facts,  together  with  the  microscopic  appear- 
ances, suggested  that  there  is  formed  a  forerunner  to  the  actual 
ferment — a  zymogen,  or  mother-ferment,  which  at  the  moment 
of  discharge  of  the  completed  secretion  is  converted  into  the 
actual  ferment.  We  might,  therefore,  speak  of  a  pepsinogen, 
typsinogen,  etc.,  and,  though  there  may  be  a  cessation  in  the 
series  of  processes,  and  no  doubt  there  is  in  some  animals,  this 
may  not  be  the  case  in  all  or  in  all  glands. 

Secretion  by  the  Stomach. — The  glands  of  the  stomach  differ 
in  most  animals  in  the  cardiac  and  pyloric  regions.  In  those 
of  the  former  zone,  both  central,  columnar,  and  parietal  (ovoid) 
cells  are  to  be  recognized.  It  was  thought  that  possibly  the 
latter  were  concerned  in  the  secretion  of  the  acid  of  the 
stomach,  but  this  is  by  no  means  certain.  Possibly  these,  like 
the  demilune  cells  of  the  pancreas,  may  be  the  progenitors  of 
the  central  (chief)  cells.  The  latter  certainly  secrete  pepsin, 
and  probably  also  rennet.  Mucus  is  secreted  by  the  cells  lining 
the  neck  of  glands  and  covering  the  raucous  membrane  inter- 
vening between  their  mouths.  The  production  of  hydrochloric 
acid  by  any  act  of  secretion  is  not  believed  in  by  all  writers, 
some  holding  that  it  is  derived  from  decomposition  of  sodium 
chloride,  possibly  by  lactic  acid.  So  simple  an  origin  is  not 
probable,  not  being  in  keeping  with  what  we  know  of  chemical 
processes  within  the  animal  body. 

Self-Digestion  of  the  Digestive  Organs. — It  has  been  found,  both 
in  man  and  other  mammals,  that  when  death  follows  in  a 
healthy  subject  while  gastric  digestion  is  in  active  progress 
and  the  body  is  kept  warm,  a  part  of  the  stomach  itself  and 
often  adjacent  organs  are  digested,  and  the  question  is  con- 
stantly being  raised,  Why  does  not  the  stomach  digest  itself 
during  life  ?  To  this  it  has  been  answered  that  the  gastric 
juice  is  constantly  being  neutralized  by  the  alkaline  blood ; 
and,  again,  that  the  very  vitality  of  a  tissue  gives  it  the  neces- 
sary resisting  powers,  a  view  contradicted  by  an  experiment 
which  is  conclusive.  If  the  legs  of  a  living  frog  be  allowed  to 
hang  against  the  inner  walls  of  the  stomach  of  a  mammal 
when  gastric  digestion  is  going  on,  they  will  be  digested. 


330  ANIMAL  PHYSIOLOGY. 

Tlie  first  view  (the  alkalinity  of  the  blood)  would  not  suffice 
to  explain  why  the  pancreas,  the  secretion  of  which  acts  best 
in  an  alkaline  medium,  should  not  be  digested. 

It  seems  to  us  there  is  a  good  deal  of  misconception  about 
the  facts  of  the  case.  Observation  on  St.  Martin  shows  that 
the  secretion  of  gastric  juice  runs  parallel  with  the  need  of  it, 
as  dependent  on  the  introduction  of  food,  its  quantity,  quality, 
etc.  Now,  there  can  be  little  doubt  that,  if  the  stomach  were 
abundantly  bathed  when  empty  with  a  large  quantity  of  its 
own  acid  secretion,  it  would  suffer  to  some  extent  at  least. 
But  this  is  never  the  case ;  the  juice  is  carried  off  and  mixed 
with  the  food.  This  food  is  in  constant  motion  and  doubtless 
the  inner  portions  of  the  cells,  which  may  be  regarded  as  the 
discharging  region,  while  the  outer  (next  the  blood  capillaries, 
the  chief  manufacturing  region  of  the  digestive  ferment)  are 
frequently  renewed. 

Such  considerations,  though  they  seem  to  have  been  some- 
what left  out  of  the  case,  do  not  go  to  the  bottom  of  the 
matter.  Amoeba  and  kindred  organisms  do  not  digest  them- 
selves. Some  believe  that  the  little  pulsatile  vacuoles  of  the 
Infusorians  are  a  sort  of  temporary  digestive  cavities. 

But,  to  one  who  sees  in  the  light  of  evolution,  it  must  be 
clear  that  a  structure  could  not  have  been  evolved  that  would 
be  self -destructive. 

The  difficulty  here  is  that  which  lies  at  the  very  basis  of  all 
life.  We  might  ask.  Why  do  living  things  live,  since  they  are 
constantly  threatened  with  destruction  from  within  as  from 
without  ?  Why  do  not  the  liver,  kidney,  and  other  glands  that 
secrete  noxious  substances,  poison  themselves  ?  We  can  not 
in  detail  explain  these  things;  but  we  wish  to  make  it  clear 
that  the  difficulty  as  regards  the  stomach  is  not  peculiar  to 
that  gland,  and  that  even  from  the  ordinary  point  of  view  it 
has  been  exaggerated. 

Comparative. — More  careful  examination  of  the  stomachs  of 
some  mammals  has  revealed  the  fact  that  in  several  animals, 
in  which  the  stomach  appears  to  be  simple,  it  is  in  reality 
compound.  There  are  different  grades,  however,  which  may 
be  regarded  as  transition  forms  between  the  true  simple 
stomach  and  that  highly  compound  form  of  the  organ  met 
with  in  the  ruminants. 

It  has  been  shown  recently  that  the  stomach  of  the  hog  has 
an  oesophageal  dilatation;  and  that  the  entire  organ  may  be 
divided  into  several  zones  with  different  kinds  of  glandular 


DIGESTION   OF  FOOD. 


331 


opifhelium,  etc.  These  portions  differ  in  digestive  power,  in 
the  characteristics  of  the  fluid  secreted,  and  other  details  be- 
yond those  which  a  superficial  examination  of  this  organ 
would  lead  one  to  suspect. 

The  stomach  of  the  horse  represents  a  more  advanced  form 
of  compound  stomach  than  that  of  the  hog,  which  is  not  evi- 
dent, however,  until  its  glandular 
structure  is  examined  closely.  The 
entire  left  portion  of  the  stomach 
represents  an  oesophageal  dilata- 
tion lined  with  an  ejjithelium  that 
closely  resembles  that  of  the  oesoph- 
agus, and  with  little  if  any  digest- 
ive function.  It  thus  appears  that 
the  stomach  of  the  horse  is  in  reali- 
ty smaller,  as  a  true  digestive  gland, 
than  it  seems,  so  that  a  great  part 
of  the  work  of  digestion  must  be 
done  in  the  intestine ;  though  in 
this  animal,  if  the  food  be  retained 
long  as  it  is  in  the  hog,  which  is 
not,  however,  the  general  opinion  as  regards  the  stomach  of  the 
horse,  salivary  digestion  may  continue  for  a  considerable  period 
after  the  food  has  left  the  mouth.  The  secretion  of  mucus  by 
the  stomach  in  herbivora  is  abundant. 


Fig.  280.— Interior  of  horse's  stomach 
(after  Chauveau).  A,  left  sac  ;  B, 
right  sac  ;  C,  duodenal  dilatation. 


The  Movements  of  the  Digestive  Organs. 


As  with  other  parts  of  the  body,  so  in  the  alimentary  tract, 
the  slower  kind  of  movement  is  carried  out  by  plain  muscu- 
lar fibers  ;  and  the  movements,  as  a  whole,  belong  to  the  class 
known  as  peristaltic ;  in  fact,  it  is  only  at  the  l)eginning  of  the 
digestive  tract  that  voluntary  (striped)  muscle  is  to  be  found 
and  to  a  limited  extent  in  the  part  next  to  this — i.  e.,  in  the 
oesophagus. 

Teeth  in  the  highly  organized  mammal  are  remarkable  in 
being  to  the  least  degree  living  structures  of  any  in  the  entire 
animal,  thus  being  in  marked  contrast  to  other  organs.  The 
enamel  covering  their  exposed  surfaces  is  the  hardest  of  all  the 
ti.ssues  and  is  necessarily  of  low  vitality.  We  have  already 
alluded  to  the  difference  in  the  teeth  of  different  animals,  and 
their  relation  to  customary  food  and  digestive  functions.  In 
fact,  it  is  clear  that  the  teeth  and  all  the  parts  of  the  digestive 


332  ANIMAL  PHYSIOLOGY. 

system  are  correlated  to  one  another.  The  compound  stomach 
of  the  ruminants,  with  its  slow  digestion  of  a  bulky  mass  of 
food,  which  must  be  softened  and  thoroughly  masticated  be- 
fore the  digestive  juices  can  attack  it  successfully,  harmonizes 
with  the  powerful  jaws,  strong  muscles  of  mastication,  and 
grinding  teeth ;  and  all  these  in  marked  contrast  with  the 
teeth  of  a  carnivorous  animal  with  its  simple  but  highly  effect- 
ive stomach.     Compare  figures  in  earlier  pages. 

Mastication  in  man  is  of  that  intermediate  character  befit- 
ting an  omnivorous  animal.  The  jaws  have  a  lateral  and 
forward-and-backward  movement,  as  well  as  a  vertical  one, 
though  the  latter  is  predominant.  The  upper  jaw  is  like  a 
fixed  millstone,  against  which  the  lower  jaw  works  as  a  nether 
millstone.  The  elevation  of  the  jaw  is  effected  by  the  mas- 
seter,  temporal,  and  internal  pterygoid  muscles  ;  depressed  by 
the  mylohyoid  and  geniohyoid,  though  principally  by  the  di- 
gastric. The  jaw  is  advanced  by  the  external  pterygoids; 
unilateral  contraction  of  these  muscles  also  produces  lateral 
movement  of  the  inferior  maxilla,  which  is  retracted  by  the 
more  horizontal  fibers  of  the  temporal. 

The  cheeks  and  tongue  likewise  take  part  in  preparing  the 
food  for  the  work  of  the  stomach,  nor  must  the  lips  be  over- 
looked even  in  man.  The  importance  of  these  parts  is  well 
illustrated  by  the  imperfect  mastication,  etc.,  when  there  is 
paralysis  of  the  muscles  of  which  they  are  formed.  Even  when 
there  is  loss  of  sensation  only,  the  work  of  the  mouth  is  done 
in  a  clumsy  way,  showing  the  importance  of  common  sensation, 
as  well  as  the  muscular  sense. 

Nervous  Supply. — The  muscles  of  the  tongue  are  governed  by 
the  hypoglossal  nerve ;  the  other  muscles  of  mastication  chiefly 
by  the  fifth.  The  afferent  nerves  are  branches  of  the  fifth  and 
glosso-pharyngeal.  It  is,  of  course,  important  that  the  food 
should  be  rolled  about  and  thoroughly  mixed  with  saliva  (in- 
salivation). 

Deglutition. — The  transportation  of  the  food  from  the  mouth 
to  the  stomach  involves  a  series  of  co-ordinated  muscular  acts 
of  a  complicated  character,  by  which  difficulties  are  overcome 
with  marvelous  success. 

It  will  be  remembered  that  the  respiratory  and  digestive 
tracts  are  both  developed  from  a  common  simple  tube — a  fact 
which  makes  the  close  anatomical  relation  between  these  two 
physiologically  distinct  systems  intelligible ;  but  it  also  involves 
•difficulties  and  dangers.    It  is  well  known  that  a  small  quantity 


DIGESTION   OF   FOOD. 


333 


of   food   or  drink  entering   the  windjjipe   produces  a  perfect 
storm  of  excitement  in  the  respiratory  system.    The  food,  there- 


'^iS.-J 


Fig.  281.— Cavities  of  mouth  and  pharynx,  etc.  (after  Sappey).  Section,  in  median  Hne,  of 
face  and  superior  portion  of  neck,  designed  to  show  the  mouth  in  its  relations  to  the  nasal 
fossa-,  pharynx,  and  larj'nx:  1,  sphenoidal  sinuses;  2,  internal  orifice  of  Eustachian  tube; 
3.  palatine  arch  ;  4.  velum  pendulum  palati  ;  5,  anterior  pillar  of  soft  palate  ;  0,  po.sterior 
pillar  of  soft  palate  ;  7,  tonsil  ;  8.  lingual  portion  of  cavity  of  pharynx  ;  0,  epiglottis  ;  10, 
section  of  hyoid  bone  ;  11,  laryngeal  portion  of  cavity  of  pharynx  ;  12,  cavity  of  larynx. 

fore,  when  it  reaches  the  oesophagus,  must  be  kept,  on  the  one 
hand,  from  entering  the  nasal,  and,  on  the  other,  the  laryngeal 
openings.  This  is  accomplished  as  follows :  When  the  food  has 
been  gathered  into  a  bolus  on  the  back  of  the  tongue,  the  tip  of 
this  organ  is  pressed  against  the  hard  palate,  by  which  the 
ma.ss  is  prevented  from  passing  forward,  and,  at  the  same  time, 
f<.»rced  back  into  the  pharynx,  the  soft  palate  being  raised  and 
the  edges  of  the  x>illars  of  the  fauces  made  to  approach  the 
uvula,  which  fills  up  the  gap  remaining,  so  that  the  posterior 
nares  are  closed  and  an  inclined  plane  provided,  over  which 
the  morsel  glides.  The  after-result  is  said  to  depend  on  the 
siz«j  of  the  bolus.     When  considerable,  the  constrictors  of  the 


334  ANIMAL  PHYSIOLOGY. 

pharynx  seize  it  and  press  it  on  into  tlie  gullet ;  when  the  mor- 
sel is  small  or  liquid  is  swallowed,  it  is  rapidly  propelled  on- 
ward by  the  tongue,  the  oesophagus  and  pharynx  being  largely 
passive  at  the  time,  though  contracting  slowly  afterward ;  at 
the  same  time  the  larynx  as  a  whole  is  raised,  the  epiglottis 
pressed  down,  chiefly  by  the  meeting  of  the  tongue  and  itself, 
while  its  cushion  lies  over  the  rima  glottidis,  which  is  closed  or 
all  but  closed  by  the  action  of  the  sphincter  muscles  of  the 
larynx,  so  that  the  food  passes  over  and  by  this  avenue  of  life, 
not  only  closed  but  covered  by  the  glottic  lid.  The  latter  is 
not  so  essential  as  might  be  supposed,  for  persons  in  whom  it 
was  absent  have  been  known  to  swallow  fairly  well.  The 
ascent  of  the  larynx  any  one  may  feel  for  himself ;  and  the  be- 
havior of  the  pharynx  and  larynx,  especially  the  latter,  may 
be  viewed  by  the  laryngoscope.  The  grip  of  the  pharyngeal 
muscles  and  the  oesophagus  may  be  made  clear  by  attaching  a 
piece  of  food  (meat)  to  a  string  and  allowing  it  to  be  partially 
swallowed. 

The  upward  movement  of  food  under  the  action  of  the  con- 
strictors of  the  pharynx  is  anticipated  by  the  closure  of  the 
passage  by  the  palato-glossi  of  the  anterior  pillars  of  the  fauces. 

The  circular  muscular  fibers  of  the  gullet  are  probably  the 
most  important  in  squeezing  on  the  food  by  a  peristaltic  move- 
ment, passing  progressively  over  the  whole  tube,  though  the 
longitudinal  also  take  part  in  swallowing,  perhaps,  by  steady- 
ing the  organ. 

Swallowing  will  take  place  in  an  animal  so  long  as  the 
medulla  oblongata  remains  intact ;  and  the  center  seems  to  lie 
higher  than  that  for  respiration,  as  the  latter  act  is  possible 
when,  from  slicing  away  the  medulla,  the  former  is  not.  An- 
encephalous  monsters  lacking  the  cerebrum  can  swallow,  suck, 
and  breathe. 

Food  placed  in  the  pharynx  of  animals  when  unconscious 
is  swallowed,  proving  that  volition  is  not  essential  to  the  act ; 
but  our  own  consciousness  declares  that  the  first  stage,  or  the 
removal  of  the  food  from  the  mouth  to  the  pharynx,  is  volun- 
tary. 

"When  we  seem  to  swallow  voluntarily  there  is  in  reality  a 
stimulus  applied  to  the  fauces,  in  the  absence  of  food  and  drink, 
either  by  the  back  of  the  tongue  or  by  a  little  saliva. 

It  thus  appears  that  deglutition  is  an  act  in  the  main  reflex, 
though  initiated  by  volition.  The  afferent  nerves  concerned 
are  usually  the  glosso-pharyngeal,  some  branches  of  the  fifth. 


DIGESTION  OP  FOOD. 


335 


and  of  the  vagus.  The  efferent  nerves  are  those  of  the  numer- 
ous muscles  concerned. 

When  food  hats  reached  the  gullet,  it  is,  of  course,  no  longer 
under  the  control  of  the  will. 

Section  of  the  vagus  or  stimulation  of  this  nerve  modifies 
the  action  of  the  oesophagus,  though  it  is  known  that  contrac- 
tions may  be  excited  in  the  excised  organ ;  but  no  doubt  nor- 
mally the  movements  of  the  gullet  arise  in  response  to  natural 
nerve  stimulation. 

Comparative. — That  swallowing  is  independent  of  gravity  is 
evident  from  the  fact  that  long-necked  animals  (horse,  giraffe) 
can  and  do  usually  swallow  with  the  head  and  neck  down,  so 
that  the  fluid  is  rolled  up  an  inclined  plane.  The  peristaltic 
nature  of  the  contractions  of  the  gullet  can  also  be  well  seen 
in  such  animals.  In  the  frog  the  gullet,  as  well  as  the  mouth, 
is  lined  with  ciliated  epithelium,  so  that  in  a  recently  killed 
animal  one  may  watch  a  slice  of  moistened  cork  disappear  from 
the  mouth,  to  be  found  shortly  afterward  in  the  stomach.  The 
rate  of  the  descent  is  surprising — in  fact,  the  movement  is 
plainly  visible  to  the  unaided  eye. 

The  Movements  of  the  Stomach. — The  stomach  of  mammals, 
including  man,  is  provided  with  three  layers  of  muscular  fibers : 
1.  External  longitudinal,  a  continuation  of  those  of  the  oesopha- 
gus.    2.  Middle  circular.     3.  Internal  oblique.     The  latter  are 


•^Jtzi^mVrh  i' 


Fio 


.  ywj. -Human  Htoma<.-h  fafter  Sttppcy).  1,  o-soiihaffiis  :  2.  circular  flbf-rs  at  wsophageal 
«ix'nln(f  :  3,  :j,  circiilur  flbtM-s  at  leswr  curvatiirn  ;  4,  4,  cin-ular  fihi-rs  at  the  |)yli»riis  ;  5,  5, 
<i.  7.  H.  «lili(|ijf  fllHTH  ;  !t,  10,  fllM-rs  of  thiH  layer  covering  the  greater  pouch  ;  II.  portion  of 
htoniach  from  which  thewj  fll>ei-8  have  been  removed  to  show  the  subjacent  circular  fibers. 


336  ANIMAL  PHYSIOLOGY. 

the  least  perfect,  viewed  as  an  investing  coat.  The  pyloric  end 
of  the  stomach  is  iDest  supplied  with  muscles  ;  where  also  there 
is  a  thick  muscular  ring  or  sphincter,  as  compared  with  which 
the  cardiac  sphincter  is  weak  and  ill-developed. 

The  movements  of  the  stomach  begin  shortly  after  a  meal 
has  been  taken,  and,  as  shown  by  observations  on  St.  Martin, 
continue  for  hours,  not  constantly,  but  periodically.  The  effect 
of  the  conjoint  action  of  the  different  sets  of  muscular  fibers  is 
to  move  the  food  from  the  cardiac  toward  the  pyloric  end  of 
the  stomach,  along  the  greater  curvature  and  back  by  the  lesser 
curvature,  while  there  is  also,  probably,  a  series  of  in-and-out 
currents  to  and  from  the  center  of  the  food-mass.  The  quantity 
of  food  is  constantly  being  lessened  by  the  removal  of  digested 
portions,  either  by  the  blood-vessels  of  the  organ  or  by  its 
passing  through  the  pyloric  sphincter.  The  empty  stomach  is 
quiescent  and  contracted,  its  mucous  membrane  being  thrown 
into  folds. 

The  movements  of  the  stomach  may  be  regarded  as  reflex, 
the  presence  of  food  being  an  exciting  cause,  though  probably 
not  the  only  one ;  and  so  largely  automatic  is  the  central  mech- 
anism concerned,  that  but  a  feeble  stimulus  suffices  to  arouse 
them,  especially  at  the  accustomed  time. 

Of  the  paths  of  the  impulses,  either  afferent  or  efferent, 
little  is  known.  Certain  effects  follow  section  or  stimulation  of 
the  vagi  or  splanchnics,  but  these  can  not  be  predicted  with 
certainty,  or  the  exact  relation  of  events  indicated. 

It  is  said  that  the  movements  of  the  stomach  cease,  even 
when  it  is  full,  during  sleep,  from  which  it  is  argued  that  gas- 
tric movements  do  normally  depend  on  the  influence  of  the 
nervous  system.  However,  the  subject  is  too  obscure  at  pres- 
ent for  further  discussion. 

Comparative. — Recent  investigations  on  the  stomach  of  the 
pig  indicate  that  in  this  animal  the  contents  of  the  two  ends  of 
the  stomach  may  long  remain  but  little  mingled ;  and  such  is 
certainly  the  case  in  this  organ  among  ruminants. 

Pathological. — Distention  of  the  stomach,  either  from  excess 
of  food  or  gas  arising  from  fermentative  changes,  or  by  secre- 
tion from  the  blood,  may  cause,  by  upward  pressure  on  the 
diaphragm,  etc.,  uneasiness  from  hampered  respiration^  and  ir- 
regularity of  the  heart,  possibly,  also,  in  part  traceable  to  the 
physical  interference  with  its  movements.  After  great  and 
prolonged  distention  there  may  be  weakened  digestion  for  a 
considerable  interval.     It  seems  not  improbable  that  this  is  to 


DIGESTION  OF   FOOD.  337 

be  explained,  not  alone  by  the  impaired  elasticity  (vitality)  of 
the  muscular  tissue,  but  also  by  defective  secreting  power.  It 
is  not  necessary  to  impress  the  lesson  such  facts  convey. 

The  Intestinal  Movements. — The  circular  fibers  i:>lay  a  much 
more  important  part  than  the  longitudinal,  being,  in  fact,  much 
more  developed.  It  is  also  to  be  remembered  that  nerves  in 
the  form  of  plexuses  (of  Auerbach  and  Meissner)  abound  in  its 
walls. 

Normally  the  movement,  slowly  progressive,  with  occasional 
lialtings,  is  from  above  downward,  stopping  at  the  ileo-csecal 
valve ;  the  movements  of  the  large  gut  being  apparently  mostly 
independent. 

Movements  may  be  excited  by  external  or  internal  stimula- 
tion, and  may  be  regarded  as  reflex ;  in  which,  however,  the 
tendency  for  the  central  cells  to  discharge  themselves  is  so 
great  (automatic)  that  only  a  feeble  stimulus  is  required,  the 
normal  one  being  the  presence  of  food. 

It  is  noticeable  in  a  recently  killed  animal,  or  in  one  in  the 
last  stages  of  asphyxia,  that  the  intestines  contract  vigorously. 
Whether  this  is  due  to  the  action  of  blood  overcharged  with 
carbonic  anhydride  and  deficient  in  oxygen  on  the  centers  pre- 
siding over  the  movements,  on  the  nerves  in  the  intestinal 
walls,  or  on  the  mugcle-cells  directly,  is  not  wholly  clear,  but  it 
is  probable  that  all  of  these  may  enter  into  the  result.  The 
vagus  nerve,  when  stimulated,  gives  rise  to  movements  of  the 
intestines,  while  the  splanchnic  seems  to  have  the  reverse  efl'ect ; 
but  the  cerebrum  itself  has  an  influence  over  the  movements  of 
the  gut,  as  is  plain  from  the  diarrhoea  traceable  to  unusual 
fear  or  anxiety.  There  is  little  to  add  in  regard  to  the  move- 
ments of  the  large  intestine.  They  are,  no  doubt,  of  consider- 
able importance  in  animals  in  which  it  is  extensive.  Normally 
they  Ijogin  at  tlie  ileo-ciecal  valve. 

Defecation. — The  removal  of  the  waste  matter  from  the  ali- 
mentary tract  is  a  complicated  process,  in  which  both  smooth 
and  striped  muscle,  the  spinal  cord,  and  the  brain  take  part. 

Defecation  may  take  place  during  the  unconsciousness  of 
sleep  or  of  disease,  and  so  be  wholly  independent  of  the  will ; 
but,  as  we  well  know,  this  is  not  usually  the  case.  Against  ac- 
cidental discharge  of  faeces  there  is  a  provision  in  the  sphinc- 
ter ani,  the  tone  of  which  is  lost  when  the  lower  part  of  the 
spinal  cord  is  destroyed.  We  are  conscious  of  being  able,  by  an 
effort  of  will,  to  prevent  the  relaxation  of  the  sphincter  or  to 
increase  its  holding  jjower,  though  the  latter  is  probably  almost 


338  ANIMAL  PHYSIOLOGY. 

wholly  due  to  the  action  of  extrinsic  muscles ;  at  all  events  any- 
one may  convince  himself  that  the  latter  may  be  made  to  take 
a  great  part  in  preventing  fsecal  discharge,  though  whether  the 
ione  of  the  sphincter  can  be  increased  or  not  by  volition  it  is 
difficult  to  say. 

What  happens  during  an  ordinary  act  of  defecation,  is  about 
as  follows :  After  a  long  inspiration  the  glottis  is  closed ;  the 
diaphragm,  which  has  descended,  remains  low,  affording,  with 
the  obstructed  laryngeal  outlet,  a  firm  basis  of  support  for  the 
action  of  the  abdominal  muscles,  which,  bearing  on  the  intes- 
tine, forces  on  their  contents,  which,  before  the  act  has  been 
called  for,  have  been  lodged  mostly  in  the  large  intestine ;  at 
the  same  time  the  sphincter  ani  is  relaxed  and  peristaltic  move- 
ments accompany  and  in  some  instances  precede  the  action  of 
the  abdominal  muscles.  The  latter  may  contract  vigorously  on 
a  full  gut  without  success  in  the  absence  of  the  intestinal  peri- 
stalsis, as  too  many  cases  of  obstinate  constipation  bear  witness. 

Like  deglutition,  and  unlike  vomiting,  there  is  usually  both 
a  voluntary  and  involuntary  part  to  the  act. 

Though  the  will,  through  the  cerebrum,  can  inhibit  defeca- 
tion, it  is  likely  that  it  does  so  through  the  influence  of  the 
cerebrum  on  some  center  in  the  cord  ;  for  in  a  dog,  the  lumbar 
cord  of  which  has  been  divided  from  the  dorsal,  the  act  is,  like 
micturition,  erection  of  the  penis,  and  others  which  are  under  the 
control  of  the  will,  still  possible,  though,  of  course,  performed 
entirely  unconsciously. 

Vomiting. — If  we  consult  our  own  consciousness  and  observe 
to  the  best  of  our  ability,  supplementing  information  thus 
gained  by  observations  on  others  and  on  the  lower  animals,  it 
will  become  apparent  that  vomiting  implies  a  series  of  co-ordi- 
nated movements,  into  which  volition  does  not  enter  either 
necessarily  or  habitually.  There  is  usually  a  preceding  nausea, 
with  a  temporary  flow  of  saliva  to  excess.  The  act  is  initiated 
by  a  deep  inspiration,  followed  by  closure  of  the  glottis. 
Whether  the  glottis  is  closed  during  or  prior  to  the  entrance 
of  air  is  a  matter  of  disagreement.  At  all  events,  the  dia- 
phragm descends  and  remains  fixed,  the  lower  ribs  being  re- 
tracted. The  abdominal  muscles  then  acting  against  this  sup- 
port, force  out  the  contents  of  the  stomach,  in  which  they  are 
assisted  by  the  essential  relaxation  of  the  cardiac  sphincter,  the 
shortening  of  the  oesophagus  by  its  longitudinal  fibers,  and  the 
extension  and  straightening  of  the  neck,  together  with  the  open- 
ing of  the  mouth. 


DIGESTION  OF  FOOD.  339 

As  the  expulsive  effort  takes  place,  it  is  accompanied  by  an 
expiratory  act  which  tends  to  keep  the  egesta  out  of  the  larynx 
and  carry  them  onward,  though  it  may  also  contribute  to  over- 
come the  resistance  of  the  elevated  soft  palate,  which  serves  to 
protect  the  nasal  passages.  The  stomach  and  oesophagus  are 
not  wholly  passive,  though  their  part  is  not  so  important  in 
the  adult  as  might  be  inferred  from  observing  vomiting  in 
infants,  the  peristalsis  of  these  organs  apparently  sufficing  in 
them  to  empty  the  stomach. 

Retching  may  be  very  violent  and  yet  ineffectual  when  the 
cardiac  sphincter  is  not  fully  relaxed.  The  pyloric  outlet  is 
usually  closed,  though  in  severe  and  long- continued  vomiting 
bile  is  often  ejected,  which  must  have  reached  the  stomach 
through  the  pylorus. 

Comparative. — The  ease  with  which  some  animals  vomit  in 
comparison  with  others  is  extraordinary,  as  in  carnivora  like 
our  dogs  and  cats :  a  matter  of  importance  to  an  animal  ac- 
customed in  the  wild  state  to  eat  entire  carcasses  of  animals — 
hair,  bones,  etc.,  included. 

The  readiness  with  which  an  animal  vomits  depends  in  great 
part  on  the  conformation  and  relations  of  the  parts  of  its  digest- 
ive tract. 

The  horse  vomits  with  difliculty — its  stomach  and  its  car- 
diac opening  being  small  and  peculiar  in  shape  (Figs.  261  and 
280),  while  its  oesophagus  is  long.  The  stomach  of  the  human 
being  during  infantile  life  is  less  pouched  than  in  the  adult, 
which  in  part  explains  the  ease  with  which  infants  vomit. 

But  the  matter  is  complex;  much  depends  on  the  proper 
co-ordinations  being  made,  and,  this  being  well  or  ill  accom- 
plished, accounts  for  the  variations  in  the  ease  with  which  dif- 
ferent persons  vomit. 

Pathological. — Vomiting  may  arise  from  the  presence  of  renal 
or  biliary  culculi  (reflex  action) ;  from  disease  of  the  cerebrum 
or  the  medulla :  from  obstruction  in  the  pyloric  region  or  in 
the  intestines:  from  emotions;  from  revived  unpleasant  m(!n- 
tal  associations;  from  nauseous  tastes,  etc.  It  may  be  ques- 
tionable whether  some  of  these  are  properly  termed  "  patho- 
logical." 

Pyro.sis  is  due  to  the  anti-peristaltic  action  of  the  stomach 
and  fiisophagus  alone,  so  that  it  is  a  sort  of  partial  vomiting 
and  allied  to  the  regurgitation  of  special  secretions, as  from  the 
crops  ()\'  [)igeons,  or  of  food  from  the  stomachs  of  ruminants. 
We  have  known  cases  in  which  anti-peristalsis  was  confined  to 


•340  ANIMAL   PHYSIOLOGY. 

the  pharynx  alone.  Some  persons  seem  to  have  acquired  the 
power  of  regurgitating  food  and  masticating  it  afresh. 

The  excessive  vomiting  following  obstruction  of  the  bowels 
is  comparable  to  the  unusual  action  of  the  heart,  ureter,  blad- 
der, etc.,  when  there  is  hindrance  to  the  outflow.  As  we  have 
already  explained  for  the  heart,  we  regard  this  as  the  resump- 
tion of  a  power  of  independent  action  seen  in  ancestral  forms 
and  marked  when  the  nervous  system  is  no  longer  exercising 
its  usual  control  and  direction.  Not  that  this  or  similar  be- 
havior may  not  result  from  excessive  stimulation,  leading  to 
unusual  central  nervous  discharge,  but  it  certainly  does  happen 
independently  of  the  nervous  system,  and  may  be  witnessed  in 
the  hearts  of  cold-blooded  animals  when  all  their  nerves  are 
divided. 

Similarly,  the  habit  of  regurgitating  the  food  is  intelligible 
in  the  light  of  evolution.  The  fact  that  mammals  are  descended 
from  lower  forms  in  which  unstriped  muscle-cells  go  to  form 
organs  that  have  a  rhythmically  contractile  function,  renders 
it  clear  why  this  function  may  become,  as  in  ruminants,  spe- 
cialized in  certain  parts  of  the  digestive  tract ;  why  carnivora 
should  vomit  readily,  and  why  human  subjects  should  learn  to 
regurgitate  food.  There  is,  so  to  speak,  a  latent  inherited  ca- 
pacity which  may  be  developed  into  actual  function.  Apart 
from  this  it  is  difficult  to  understand  such  cases  at  all. 

The  vomiting  center  is  usually  located  in  the  medulla,  and 
is  represented  as  working  in  concert  with  the  respiratory  center. 
But  when  we  consider  that  there  is  usually  an  increased  flow 
of  saliva  and  other  phenomena  involving  additional  central 
nervous  influence,  we  see  reason  to  believe  in  co-ordinated 
action  implying  the  use  of  parts  of  the  central  nervous  system 
not  so  closely  connected  anatomically  as  the  respiratory  and 
vomiting  centers  are  assumed  to  be. 

Indeed,  as  we  before  indicated,  it  does  not  seem  probable 
that  the  doctrine  of  centers  in  its  present  form,  especially  with 
such  precise  limitations,  both  anatomically  and  physiologically, 
will  continue  to  be  maintained.  We  seem  to  have  been  over- 
looking the  connection  of  parts  while  occupied  with  defining 
their  limits.  It  is  not,  however,  yet  possible  to  substitute 
other  explanations  that  shall  be  wholly  satisfactory ;  and  we 
make  these  remarks  to  keep  the  student  expectant  of  progress, 
for,  as  a  distinguished  exponent  of  science  has  said,  "  When 
Science  adopts  a  [rigid]  creed,  she  commits  suicide." 

We  do  not  know  the  part  taken,  if  any,  by  the  splanchnic 


DIGESTION   OP   FOOD.  34I 

or  other  nerves  of  the  sympathetic  system ;  but,  from  the  fact 
that  discharge  of  the  gastric  contents  is  impossible  when  the 
vagi  are  cut,  it  is  likely  that  the  efferent  impulses,  determining 
the  relaxation  of  the  cardiac  sphincter,  descend  by  these  nerves, 
while  the  chorda  tympani  is  concerned,  of  course,  in  the  secre- 
tion of  saliva.  But  it  will  be  clear,  from  the  facts  of  the  case, 
that  many  nerves,  both  afferent  and  efferent,  are  concerned ; 
and  it  is  more  than  likely  that  our  explanations  of  the  entire 
process  are  quite  inadequate  to  unravel  its  real  complexity. 

Therapeutics. — The  evidence  from  the  use  of  drugs  seems  to 
emphasize  the  last  statement.  At  all  events,  emetics  act  in  a 
variety  of  ways,  and  differently  in  different  animals. 

The  Removal  op  Digested  Products  from  the  Aliment- 
ary Canal. 

The  glands  of  the  stomach  are  simply  secretive,  and  all  ab- 
sorption from  this  organ  is  either  by  blood-vessels  directly  or 
by  lymphatics ;  at  least,  such  is  the  ordinary  view  of  the  sub- 
ject— whether  it  is  not  too  narrow  a  one  remains  to  be  seen. 

It  is  imjjortant  to  remember  that  the  intestinal  mucous 
membrane  is  supplied  not  only  with  secreting  glands  but  lym- 
phatic tissue,  in  the  form  of  the  solitary  and  agminated  glands 
(Peyer's  patches)  and  thickly  studded  with  villi,  giving  the 
small  gut  that  velvety  appearance  appreciable  even  by  the 
naked  eye. 

It  will  not  be  forgotten  that  the  capillaries  of  the  digestive 
organs  terminate  in  the  veins  of  the  portal  system,  and  that  the 
blood  from  these  parts  is  conducted  through  the  liver  before  it 
reaches  the  general  circulation. 

The  lymphatics  of  these  organs  form  a  part  of  the  general 
lymphatic  system  of  the  body  ;  but  the  peculiar  way  in  which 
absorj>tion  is  effected  by  villi,  and  the  fact  that  the  lymphatics 
of  the  intestine,  etc.,  at  one  time  (fasting)  contain  ordinary 
lymph  and  at  another  (after  meals)  the  products  of  digestion, 
imparts  to  them  a  physiological  character  of  their  own. 

Absorption  will  be  the  better  understood  if  we  treat  now  of 
lymph  and  chyle  and  the  lymph  vascular  system,  which  were 
jjurposely  postponed  till  the  present;  though  its  connection 
with  the  vascular  system  is  as  close  and  important  as  with 
the  digestive  organs. 

The  lymphatic  system,  as  a  whole,  more  closely  resembles 
the  venous  than  the  artcsrial  vessels.     "Wo  may  speak  (jf  lym- 


342 


ANIMAL   PHYSIOLOGY. 


phatic  capillaries,  which  are,  in  essential  points 
of  structure,  like  the  arterial  capillaries ;  while 
the  larger  vessels  may  be  compared  to  veins, 
though  thinner,  being  provided  with  valves  and 
having  very  numerous  anastomoses.  These 
lymphatic  capillaries  begin  in  spaces  between 
the  tissue-cells,  from  which  they  take  up  the 
effete  lymph.  It  is  interesting  to  note  that 
there  are  also  perivascular  lymphatics,  the  ex- 
istence of  which  again  shows  how  close  is  the 
relation  between  the  blood  vascular  and  lym- 
phatic systems,  and  as  we  would  suppose,  and 
as  is  actually  found  to  be  the  case,  between  the 
contents  of  each. 

Lymph  and  Chyle. — If  one  compares  the  mes- 
entery in  a  kitten,  when  fasting,  with  the  same 
part  in  an  animal  that  was  killed  some  hours 
after  a  full  meal  of  milk,  it  may  be  seen  that 
the  formerly  clear  lines  indicating  the  course  of 
the  lymphatics  and  ending  in  glands  have  in 
the    latter  case  become    whitish   (hence  their 

name,  lacteals),  owing  to  the  absorption  of  the  emulsified  fat  of 

the  milk. 


Fig.  283.— Valves  ot 
lymphatics  (Sappey). 


Fig.  284.— Origin  of  lymphatics  (after  Landois).  I.  From  central  tendon  of  diaphragm  of 
rabbit  (semi-diagrammatic) ;  s,  lymph-canals  communicating  by  X  with  lymphatic  vessel 
L ;  A,  origin  of  lymphatic  by  union  of  lymph-canals  ;  E,  E,  endothelium.  U.  Perivas- 
cular canal. 


DIGESTION   OP   FOOD. 


343 


Microscopic  examination  shows  the  chyle  tu  contain  (when 
coagulated)  librin,  many  leucocytes,  a  few  developing  red  cor- 
puscles, an  abundance  of  fat  in  the  form  both  of  very  minute 
oil-globules  and  particles  smaller  still. 


Fig.  285.— Epithelium  from  duodenum  of  rab- 
bit, two  hours  after  having  been  fed  with 
melted  butter  (Funke) 


Fig.  286.— VilU  filled  with  fat,  from  small 
intestine  of  an  executed  criminal,  one 
hour  after  death  ( Funke). 


There  are  also  present  fatty  acids,  soaps  small  in  quantity 
as  compared  with  the  neutral  fats,  also  a  little  cholesterin  and 
lecithin.  But  chyle  varies  very 
widely  even  in  the  same  animal 
at  different  times.  To  the  above 
mu.st  be  added  proteids  (fibrin, 
serum-albumin,  and  globulin) ; 
extractives  (sugar,  urea,  leu- 
cin) ;  and  salts  in  which  sodium 
chloride  is  abundant. 

The  composition  of  lymph  is 
so  similar  to  that  of  chyle,  and 
both  to  blood,  that  lymph 
might,  with  a  fair  degree  of  ac- 
curacy, be  regarded  as  blood 
without  its  red  corpuscles,  and 
chyle  as  lymph  with  much  neu- 
tral fat  in  a  very  fine  state  of 
divisirjn. 

The  Movements  of  the  Lymph — comparative.— In  some  fishes, 
.some  birds,  and  amphibians,  there  are  lymph  hearts. 

In  the  frog  there  are  two  axillary  and  two  sacral  lymph 
hearts.  The  latter  are,  especially,  easily  seen,  and  there  is  no 
doubt  that  they  are  under  the  control  of  tlie  nervous  system. 


Fig.  287.— Chyle   taken 
and  thoracic  duct 


from    the    lacteala 
f    a    criminal    exe- 


cuted during  digestion  (Funke).  Shows 
leucocytes  and  excessively  fine  granules 
of  fatty  emulsion. 


344 


ANIMAL   PHYSIOLOGY. 


In  the  mammals  no  such  special  helps  for  the  propulsion  of 
lymph  exist. 

There  is  little  doubt  that  the  blood  -  pressure  is  always 
higher  than  the  lymph-pressure,  and  when  the  blood-vessels 


Fig.  288.— Thoracic  duct  (Mascagni)     1,  thoracic  duct ,  2,  great  lymphatic  duct ;  3,  recep- 
taculum  chyli ;  4,  curve  of  thoracic  duct  ]ust  before  it  empties  mto  the  venous  system. 

are  dilated  the  fluid  within  the  perivascular  lymph-channels  is 
likely  compressed ;  muscular  exercise  must  act  on  the  lymph- 
channels  as  on  veins,  both  being  provided  w,ith  valves,  though 
themselves  readily  compressible ;  the  inspiratory  efforts,  espe- 
cially when  forcible,  assist  in  two  ways :  by  the  compressing 
effect  of  the  respiratory  muscles,  and  by  the  aspirating  effect 
of  the  negative  pressure  within  the  thorax,  producing  a  similar 
aspirating  effect  within  the  great  veins,  into  which  the  large 
lymphatic  trunks  empty.  The  latter  are  provided  at  this  point 
with  valves,  so  that  there  is  no  back-flow ;  and,  with  the  posi- 
tive pressure  within  the  large  lymphatic  trunks  (thoracic  duct, 
etc.),  the  physical  conditions  are  favorable  to  the  outflow  of 
lymph  or  chyle. 


DIGESTION  OP   FOOD. 


345 


Onr  knowledge  of  the  nature  of  the  passage  of  the  chyle 
from  the  intestines  into  the  blood  is  now  clearer  than  it  was  till 
recently,  though  still  incomplete. 

The  exact  structure  of  a  villus  is  to  be  carefully  considered. 
If  we  assume  that  the  muscular  cells  in  its  structure  have  a 
rhythmically  contractile  function,  the  blind  terminal  portion 
of  the  lacteal  inclosed  within  the  villus  must,  after  being 
emptied,  act  as  a  suction-pump  to  some  extent ;  at  all  events, 
the  conditions  as  to  pressure  would  be  favorable  to  inflow  of 
any  material,  especially  fluid  without  the  lacteal.  The  great 
difficvilty  hitherto  was  to  understand   how  the  fat  found  its 


Kir;.  28t>.— Lymphatic  vessels  and  plands  (Sappey).  1,  upper  extremity  of  thoracic  duct,  pass- 
iDK  behind  the  inU^rnal  jugular  vein  ;  2.  ofjening  of  thoracic  duct  into  internal  jugular  and 
left  Hubclavian  vein.    Lymphatic  glands  are  seen  in  (;ourse  of  vessels. 


way  tlirough    the   villus  into  tlie  Ijlood,  for,  that  most  of   it 
passes  in  this  direction  there  is  little  doubt. 

It  is  now  known  that  leucocytes  (amneboids,  phagocytes) 
migrate  fnmi  within  the  villus  outward,  and  may  even  reach 
its  surffice ;   that  they   take   uj)   (eat)  fat-particles   fiom   the 


346 


ANIMAL   PHYSIOLOGY. 


Fig.  290.— Stomach,  intestine,  and  mesentery,  with  mesenteric  blood-vessels  and  lacteals 
(slightly  reduced  from  a  figure  in  the  original  work  of  Asellius,  published  in  1628)  (after 
Flint).  A,  A,  A,  A,  A,  mesenteric  arteries  and  veins  ;  B,  B,  B,  B,  B,  B,  B,  B,  B,  B,  lacteals  ; 
C,  C,  C,  C,  mesentery  ;  D,  D,  stomach  ;  E,  pyloric  portion  of  stomach  ;  F,  duodenum  ; 
G",  O,  G,  jejunum  ;  H,  H,  H,  H,  H,  ileum  ;  I,  artery  and  vein  on  fundus  of  stomach  ;  K, 
portion  of  omentum. 

epitlieliuin  of  the  villus,  and,  indepen(iently  themselves,  carry 
them  inward,  reach  the  central  lacteal  and  break  up,  thus  releas- 
ing the  fat.     How  the  fat  gets  into  the  covering  epithelium  is 


DIGESTION   OF   FOOD. 


347 


not  yet  so  fully  known — possibly  by  a  simi- 
lar inceptive  process  ;  nor  is  it  ascertained 
■what  constructive  or  other  chemical  pro- 
cesses they  may  perform  ;  though  it  is  not 
at  all  likely  that  the  work  of  the  amoeboid 
cells  is  confined  to  the  transport  of  fat 
alone,  but  that  other  matters  are  also  thus 
removed  inward  to  the  lacteal. 

Experimental. — If  two  frogs  under  the 
influence  of  urari,  to  remove  the  effect  of 
muscular  movements,  be  placed  under  ob- 
servation, the  one  having  its  brain  and 
spinal  cord  destroyed,  the  other  intact,  in 
both  the  aorta  divided  across,  and  normal 
saline  solution  injected  into  the  posterior 
lymi^h-sac  (beneath  the  skin  of  the  back), 
it  will  be  found,  on  suspending  the  two 
by  the  lower  jaw,  that,  in  the  frog  with 
the  nerve  -  centers  uninjured,  abundance 
of  saline  fluid  is  taken  up  from  the  dor- 
sal sac  and  expelled  through  the  aorta, 
but  in  the  other  case  none,  the  heart  remaining  all  but  empty. 


Fig.  ;iyi.— Intestinal  villus 
(after  Leydig).  a,  a,  a, 
epithelial  covering  ;  b, 

b,  capillary    network  ; 

c,  c,  longitudinal  mus- 
cular fibers  ;  d,  lacteal. 


ITio.  292,— A.  Villi 


)f   man,  showiiij^   blood-veasels   and   lacteals  ; 
(!h(iuvi'(iiii 


Villus  of  sherp  Caften" 


348 


ANIMAL   PHYSIOLOGY. 


Different  interpretations  have  been  put  upon  this  experi- 
ment.    Some  point  to  it  as  clear  proof  of  the  influence  of  the 


str 


Fig.  293.— a.  Section  of  villus  of  rat  killed  during  fat  absorption  (Schafer).  ep,  epithelium  ; 
str,  striated  border  ;  c,  lymph-cells  :  c',  lymph-cells  in  epithelium  ;  I,  central  lacteal  con- 
taining disintegrating  corpuscles.  B.  Mucous  membrane  of  frog's  intestine  during  fat 
absorption  (Schafer).    ep,  epithelium ;  s^r,  striated  border;  C,  lymph-corpuscles;  i,  lacteal. 


nervous  system  directly ;  to  others  it  seems  that  the  failure  of 
absorption  is  owing  to  the  greatly  dilated  condition  of  the 
blood-vessels,  consequent  upon  the  loss  of  arterial  tone,  the 
blood  remaining  in  the  veins,  and  the  circulation  being,  in  fact, 
practically  arrested.  It  certainly  can  not  be  claimed  that  the 
first  conclusion  necessarily  follows  from  the  experiment;  the 
second  may  be  a  partial  explanation  of  the  failure  of  absorp- 
tion; but,  when  a  multitude  of  other  facts  are  taken  into 
account,  there  seems  little  reason  to  doubt  that  so  important  a 
process  as  absorption  can  not  fail  to  be  regulated  by  the  nerv- 
ous centers.  The  danger  of  founding  any  important  conclu- 
sion on  a  single  experiment  is  very  great. 

Again,  if  the  leg  of  a  frog,  exclusive  of  the  nerves,  be  liga- 
tured, the  limb  will  be  found  to  swell  rapidly  if  placed  in  water, 
which  is  not  true  of  a  dead  limb.  This  is  adduced  as  evidence 
for  the  independence  of  the  absorptive  process  and  the  circula- 
tion; and,  since  section  of  the  sciatic  nerve  is  said  to  arrest 
absorption,  such  an  experiment,  taken  together  with  the  two 


DIGESTION   OF   FOOD.  349 

preAions  ones,  points  in  the  direction  of  the  control  of  this 
process  by  the  nervous  system.  But  if  the  views  we  hold  of 
the  absolute  dependence,  especially  in  the  higher  animals,  of 
all  "s^tal  processes  on  the  nervous  system  are  correct,  it  fol- 
lows, as  a  matter  of  course,  that  absorption  in  living  tissues, 
which  we  do  not  regard  as  wholly  explicable  by  any  physical 
process,  but  as  bound  up  with  all  the  functions  of  cell-life, 
must  be  dependent  on  that  connection  we  are  endeavoring  to 
emphasize  between  one  tissue  and  another,  and  especially  the 
dominating  tissue,  the  nervous  system. 

There  are  two  points  that  are  very  far  from  being  deter- 
mined :  the  one  the  fate  of  the  products  of  digestion ;  the  other 
the  exact  limit  to  which  digestion  is  carried.  How  much — 
e.  g.,  of  proteid  matter — does  actually  undergo  conversion  into 
peptone ;  how  much  is  converted  into  leucin  and  tyrosin ;  or, 
again,  what  proportion  of  the  albuminous  matters  are  dealt  with 
as  such  by  the  intestine  without  conversion  into  peptone  at  all, 
either  as  soluble  proteid  or  in  the  form  of  solid  particles  ? 

1,  It  is  generally  believed  that  soluble  sugars  are  absorbed, 
usually  after  conversion  into  maltose  or  glucose,  by  the  capil- 
laries of  the  stomach  and  intestine. 

2.  There  is  some  positive  evidence  of  the  presence  of  fats, 
soaps,  and  sugars  in  unusual  amount  after  a  meal  in  the  portal 
vein,  which  implies  removal  from  the  intestinal  contents  by 
the  capillaries,  though,  so  far  as  experiment  goes,  the  fat  is 
chiefly  in  the  form  of  soaps. 

Certain  experiments  have  been  made  b^^  ligating  the  pyloric 
end  of  the  stomach,  by  introducing  a  cannula  into  the  thoracic 
duct,  so  as  to  continually  remove  its  contents,  etc.  But  we  are 
surprised  that  serious  conclusions  should  have  been  drawn  under 
such  circumstances,  seeing  that  the  natural  conditions  are  so 
altered.  What  we  wish  to  get  at  in  physiology  is  the  normal 
function  of  parts,  and  not  the  possible  results  after  our  inter- 
ference. Under  such  circumstances  the  phenomena  may  have 
a  suggestive  but  certainly  can  not  have  a  conclusive  value. 

It  is  a  very  striking  fact  that  little  peptone  (none,  according 
to  some  observers)  can  be  detected  even  in  the  portal  blood. 
True  it  is,  the  circulation  is  rapid  and  constant,  and  a  small 
quantity  might  e.s(;ape  detection,  yet  a  considerable  amount  be 
removed  from  the  intestine  in  the  space  of  a  few  hours  by  the 
capillaries  alone,  Pej^tone  is  not  found  in  the  cojitents  of  the 
thoracic  duct. 

Recent  investigations  have  thrown  a  new  light  on  p(!ptone. 


350  ANIMAL   PHYSIOLOGY. 

It  is  now  known  that  there  are  several  kinds  of  peptones,  a 
disclosure  for  which  we  were  not  unprepared,  considering  our 
imperfect  knowledge  of  proteids  in  general ;  but  there  have 
been  other  developments  which,  on  the  supposition  that  the 
peptone  of  the  alimentary  canal  is  freely  absorbed  as  such,  are 
startling  enough.  It  has  been  shown  that  these  peptones,  at 
least  as  prepared  by  artificial  digestion,  have  three  efi^ects  when 
injected  in  quantity  into  the  blood  of  an  animal :  They  produce 
narcosis ;  they  retard  or  prevent  coagulation  of  the  blood ;  they 
lower  blood-pressure.  The  first  effect  may  be  dependent  in 
whole  or  in  part  on  the  third. 

But,  inasmuch  as  the  venom  of  poisonous  reptiles,  according 
to  recent  investigations,  is  essentially  proteid  in  nature,  it  is 
plain  that  we  must  exercise  great  caution  in  drawing  conclu- 
sions in  regard  to  the  physiological  effects  of  proteid  bodies,  so 
long  as  our  knowledge  of  their  exact  chemical  composition  is 
so  imperfect.  That  the  chemist  can  make  out  no  great  differ- 
ence between  peptones  prepared  in  the  laboratory  and  the  di- 
gestive tract,  or  even  between  these  and  snake- venom,  though 
they  haye  such  different  effects  when  injected  into  the  blood, 
is  clear  proof  of  how  much  we  have  yet  to  learn  of  these 
bodies. 

But  we  introduce  these  considerations  here  rather  to  show 
that  it  is  by  no  means  likely  that  any  great  quantity  of  pep- 
tones passes  into  the  blood  as  such  at  any  one  time.  It  has 
been  recently  suggested  that  peptone  is  converted  into  globulin 
in  the  liver.  But  what  proof  is  there  of  this  ?  And  already 
we  have  credited  the  liver  with  a  large  share  of  work. 

For  a  considerable  period  it  has  been  customary  to  use  the 
terms  endosmosis  and  diffusion  in  connection  with  the  func- 
tions of  the  alimentary  canal,  and  especially  the  intestinal  tract, 
as  if  this  thin- walled  but  complicated  organ,  or  rather  collec- 
tion of  organs,  were  little  more,  so  far  as  absorption  is  con- 
cerned, than  a  moist  membrane,  leaving  the  process  of  the  re- 
moval of  digested  food  products  to  be  explained  almost  wholly 
on  physical  principles. 

From  such  views  we  dissent.  We  believe  they  are  opposed 
to  what  we  know  of  living  tissue  everywhere,  and  are  not  sup- 
ported by  the  special  facts  of  digestion.  When  certain  foreign 
bodies  (as  purgatives)  are  introduced  into  the  blood  or  the  ali- 
mentary canal,  that  diffusion  takes  place,  according  to  physical 
laws,  may  indicate  the  manner  in  which  the  intestine  can  act ; 
but  even  admitting  that  under  such  circumstances  physical 


DIGESTION  OF    FOOD.  351 

principles  actually  do  explain  the  whole,  which  we  do  not  grant, 
it  would  by  no  means  follow  that  such  was  the  natural  behav- 
ior of  this  organ  in  the  discharge  of  its  ordinary  functions. 

When  we  consider  that  the  blood  tends  to  maintain  an  equi- 
librium, it  must  be  evident  that  the  removal  of  substances  from 
the  alimentary  canal,  unless  there  is  to  be  excessive  activity  of 
the  excretory  organs  and  waste  of  energy  both  by  them  and 
the  digestive  tract,  must  in  some  degree  depend  on  the  demand 
for  the  products  of  digestion  by  the  tissues.  That  there  is  to 
some  extent  a  corrective  action  of  the  excretory  organs  always 
going  on  is  no  doubt  true,  and  that  it  may  in  cases  of  emergency 
be  great  is  also  true ;  but  that  this  is  minimized  in  ways  too 
complex  for  us  to  follow  in  every  detail  is  equally  true.  Diges- 
tion waits  on  appetite,  and  the  latter  is  an  expression  of  the 
needs  of  the  tissues.  We  believe  it  is  literally  true  that  in  a 
healthy  organism  the  rate  and  character  of  digestion  and  of 
the  removal  of  prepared  products  are  largely  dependent  on  the 
condition  of  the  tissues  of  the  body. 

Why  is  digestion  more  perfect  in  overfed  individuals  after 
a  short  fast  ?  The  whole  matter  is  very  complex,  but  w:e  think 
it  is  infinitely  better  to  admit  ignorance  than  attempt  to  ex- 
plain by  principles  that  do  violence  to  our  fundamental  con- 
ceptions of  life  processes.  To  introduce  "  ferments  "  to  explain 
so  many  obscure  points  in  physiology,  as  the  conversion  of 
jjeptone  in  the  blood,  for  example,  is  taking  refuge  in  a  way 
that  does  no  credit  to  science. 

Without  denying  that  endosmosis,  etc.,  may  play  a  part  in 
the  vital  processes  we  are  considering,  we  believe  a  truer  view 
of  the  whole  matter  will  be  ultimately  reached.  In  the  mean 
time  we  think  it  best  to  express  our  belief  that  we  are  ignorant 
of  the  real  nature  of  absorption  in  great  part ;  but  we  think 
that,  if  the  alimentary  tract  were  regarded  as  doing  for  the 
digested  food  (chyle,  etc.)  some  such  work  as  certain  other 
glands  do  for  the  blood,  we  would  be  on  the  way  to  a  truer  con- 
(;eption  of  the  real  nature  of  the  processes. 

It  would  then  be  possible  to  understand  that  proteids  either 
in  the  form  of  soluble  or  insoluble  substances,  including  pep- 
tone, might  be  taken  in  hand  and  converted  by  a  true  vital 
pro(;ess  into  the  constituents  of  the  blood. 

If  we  were  to  regard  the  kidney  as  manufacturing  useful 
instead  of  harmful  pn^ducts,  the  resemblance  in  behavior  would 
in  many  points  b<;  parallel.  We  have  seen  that  mechanical 
ex]>lajiHtions  of  llic   functions  of  tin-  kidiu-y  have  failed,  and 


352  ANIMAL   PHYSIOLOGY. 

that  it  must  be  regarded  even  in  those  parts  that  eliminate 
most  water  as  a  genuine  secreting  mechanism. 

We  wish  to  present  a  somewhat  truer  conception  of  the 
lymph  that  is  separated  from  the  capillaries  and  bathes  the 
tissues. 

We  would  regard  its  separation  as  a  true  secretion,  and  not 
a  mere  diffusion  dependent  wholly  on  blood-pressure.  The 
mere  ligature  of  a  vein  does  not  suffice  to  cause  an  excess  of 
diffusion,  but  the  vaso-motor  nerves  have  been  shown  to  be 
concerned.  The  effusions  that  result  from  pathological  pro- 
cesses do  not  correspond  with  the  lymph — that  is,  the  nutrient 
material — provided  by  the  capillaries  for  the  tissues.  These 
vessels  are  more  than  mere  carriers ;  they  are  secretors — in  a 
sense  they  are  glands.  We  have  seen  that  in  the  foetus  they 
function  both  as  respiratory  and  nutrient  organs  in  the  allan- 
tois  and  yelk-sac,  and,  in  our  opinion,  they  never  wholly  lose 
this  function. 

The  kind  of  lymph  that  bathes  a  tissue,  we  believe,  depends 
on  its  nature  and  its  condition  "at  the  time,  so  that,  as  we  view 
tissue-lymph,  it  is  not  a  mere  effusion  with  which  the  tissues, 
for  which  it  is  provided,  have  nothing  to  do.  The  differences 
may  be  beyond  our  chemistry  to  determine,  but  to  assume  that 
all  lymph  poured  out  is  alike  is  too  crude  a  conception  to  meet 
the  facts  of  the  case.  Glands,  too,  it  will  be  remembered,  derive 
their  materials,  like  all  other  tissues,  not  directly  from  the 
blood,  but  from  the  lymph.  We  believe  that  the  cells  of  the 
capillaries,  like  all  others,  are  influenced  by  the  nervous  system, 
notwithstanding  that  nerves  have  not  been  traced  terminating 
in  them. 

It  is  to  be  borne  in  mind  that  the  lymph,  like  the  blood, 
receives  tissue  waste-products — in  fact,  it  is  very  important  to 
realize  that  the  lymph  is,  in  the  first  instance,  a  sort  of  better 
blood — an  improved,  selected  material,  so  far  as  any  tissue  is 
concerned,  which  becomes  gradually  deteriorated  (see  Fig.  329). 

We  have  not  the  space  to  give  all  the  reasons  on  which  the 
opinions  expressed  above  are  founded ;  but,  if  the  student  has 
become  imbued  with  the  principles  that  pervade  this  work  thus 
far,  he  will  be  prepared  for  the  attitude  we  have  taken,  and 
sympathize  with  our  departures  from  the  mechanical  (physical) 
physiology. 

We  think  it  would  be  a  great  gain  for  physiology  if  the  use 
of  the  term  "  absorption,"  as  applied  to  the  alimentary  tract, 
were  given  up  altogether,  as  it  is  sure  to  lead  to  the  substitu- 


DKJESTIOX    OF    FOOD.  353 

tion  of  the  gross  conceptions  of  physical  processes  instead  of 
the  subtle  though  at  present  rather  indefinite  ideas  of  vital 
processes.  We  prefer  ignorance  to  narrow,  artificial,  and  erro- 
neous views. 

Pathological. — Under  certain  circumstances,  of  which  one  is 
obstruction  to  the  venous  circulation  or  the  lymphatics,  fluid 
may  be  poured  out  or  effused  into  the  neighboring  tissues  or  the 
serous  cavities.  This  is  of  very  variable  composition,  but  always 
contains  enough  salts  and  proteids  to  remind  one  of  the  blood. 

Such  fluids  are  often  spoken  of  as  "  lymph,"  though  the 
resemblance  to  normal  tissue-lymph  is  but  of  the  crudest  kind ; 
and  the  condition  of  the  vessels  when  it  is  secreted,  if  such  a 
term  is  here  appropriate,  is  not  to  be  compared  to  the  natural 
separation  of  the  normal  lymph — in  fact,  were  this  not  so,  it 
would  be  like  the  latter,  which  it  is  not.  When  such  effusions 
take  place  they  are  in  themselves  evidence  of  altered  (and  not 
merely  increased)  function. 

The  Faeces. — The  faeces  may  be  regarded  in  at  least  a  three- 
fold aspect.  They  contain  undigested  and  indigestible  rem- 
nants, the  ferments  and  certain  decomposition  products  of  the 
digestive  fluids,  and  true  excretory  matters. 

In  carnivorous  and  omnivorous  animals,  including  man, 
the  undigested  materials  are  those  that  have  escaped  the  action 
of  the  secretions — such  as  starch  and  fats — together  with  those 
substances  that  the  digestive  juices  are  powerless  to  attack, 
as  horny  matter,  hairs,  elastic  tissue,  etc. 

In  vegetable  feeders  a  larger  proportion  of  chlorophyl,  cel- 
lulose, and  starch  will,  of  course,  be  found. 

These,  naturally,  are  variable  with  the  individual,  the  spe- 
cies, and  the  vigor  of  the  digestive  organs  at  the  time. 

Besides  the  above,  certain  products  are  to  be  detected  in  the 
f£eces  plainly  traceable  to  the  digestive  fluids,  and  showing 
that  tliey  have  undergone  chemical  decomposition  in  the  ali- 
mentary tract,  such  as  cholalic  acid,  altered  coloring-matters 
like  urobilin,  derivable  probably  from  bilirubin ;  also  choles- 
terine,  fatty  acids,  insolulile  soaps  (calcium,  magnesium),  to- 
gether with  ferments,  having  the  properties  of  pepsin  an<l 
amylopsin.     Mucus  is  also  abundant  in  the  faeces. 

We  know  little  of  the  excretory  products  proper,  as  they 
probably  normally  exist  in  small  quantity,  and  it  is  not  impos- 
sible that  some  of  the  products  of  the  decomposition  of  the 
digestive  juices  may  be  reabsorbed  and  worked  over  or  excreted 
by  the  kidneys,  etc. 

23 


354  ANIMAL  PHYSIOLOGY. 

There  is,  however,  a  recognized  non-nitrogenous  crystalline 
body  known  as  excretin,  which  contains  sulphur,  salts,  and 
pigments,  and  that  may  rank  perhaps  as  a  true  excretion  of 
the  intestine. 

It  is  well  known  that  bacteria  abound  in  the  alimentary 
tract,  though  their  number  is  dependent  on  a  variety  of  circum- 
stances, including  the  kind  of  food  and  the  condition  in  which 
it  is  eaten.  These  minute  organisms  feed,  of  course,  and  to  get 
their  food  produce  chemical  decompositions.  SJcatol  and  indol 
are  possibly  thus  produced,  and  give  the  fgecal  odor  to  the  con- 
tents of  the  intestine.  But  as  yet  our  ignorance  of  these  mat- 
ters is  greater  than  our  knowledge — a  remark  which  applies  to 
the  excretory  functions  of  the  alimentary  tract  generally. 

Pathological. — The  facts  revealed  by  clinical  and  pathological 
study  leave  no  doubt  in  the  mind  that  the  intestine  at  all  events 
may,  when  other  glands,  like  the  kidney,  are  at  fault,  undertake 
an  unusual  share  of  excretory  work,  probably  even  to  the  length 
of  discharging  urea. 

Obscure  as  the  subject  is,  and  long  as  it  may  be  before  we 
know  exactly  what  and  how  matter  is  thus  excreted,  we  think 
that  it  will  greatly  advance  us  toward  a  true  conception  of  the 
vital  processes  of  the  mammalian  body  if  we  regard  the  ali- 
mentary tract  as  a  collection  of  organs  with  both  a  secreting 
and  excreting  function ;  that  what  we  have  been  terming  ab- 
sorption is  in  the  main,  at  least,  essentially  secretion  or  an  allied 
process;  and  that  the  parts  of  this  long  train  of  organs  are 
mutually  dependent  and  work  in  concert,  so  that,  when  one  is 
lacking  in  vigor  or  resting  to  a  greater  or  less  degree,  the  others 
make  up  for  its  diminished  activity  ;  and  that  the  whole  must 
work  in  harmony  with  the  various  excretory  organs,  as  an 
excretor  itself,  and  in  unison  with  the  general  state  of  the  econ- 
omy. We  are  convinced  that  even  as  an  excretory  mechanism 
one  part  may  act  (vicariously)  for  another. 

Of  course,  in  disease  the  condition  of  the  faeces  is  an  indica- 
tion of  the  state  of  the  digestive  organs ;  thus  color,  consistence, 
the  presence  of  food  in  lumps,  the  odor,  and  many  other  points 
tell  a  plain  story  of  work  left  undone,  ill-done,  or  disordered 
by  influences  operating  from  within  or  from  without  the  tract. 
The  intelligent  physician  acts  the  part  of  a  qualified  inspector, 
surveying  the  output  of  a  great  factory,  and  drawing  conclu- 
sions in  regard  to  the  kind  of  work  which  the  operatives  have 
performed. 


DIGESTION   OP   FOOD. 


355 


The  Changes  produced  in  the  Food  in  the  Alimentary 

Canal. 

We  have  now  considered  the  method  of  secretion,  the  secre- 
tions themselves,  and  the  movements  of  the  various  parts  of 
the  digestive  tract,  so  that  a  brief  statement  of  the  results  of 
all  this  mechanism,  as  represented  by  changes  in  the  food,  will 
be  appropriate.  We  shall  assume  for  the  present  that  the  effects 
of  the  digestive  juices  are  substantially  the  same  in  the  body 
as  in  artificial  digestion. 

Among  mammals  food  is,  in  the  mouth,  comminuted  (except 
in  the  case  of  the  carnivora,  that  bolt  it  almost  whole,  and  the 
ruminants,  that  simply  swallow  it  to  be  regurgitated  for  fresh 
and  complete  mastication),  insalivated,  and,  in  most  species, 
chemically  changed,  but  only  in  so  far  as  starch  is  concerned. 

Deglutition  is  the  result  of  the  co-ordinated  action  of  many 
muscular  mechanisms,  and  is  reflex  in  nature.  The  oesophagus 
secretes  mucus,  which  lubricates  its  walls,  and  aids  mechan- 
ically in  the  transport  of  the  food  from  the  mouth  to  the  stom- 
ach. In  the  stomach,  by  the  action  of  the  gastric  juice,  food 
is  further  broken  up,  the  proteid  covering  of  fat-cells  is  digested, 
and  the  structure  of  muscle,  etc.,  disappears.     Proteid  matters 


Flo.  291— Matten*  taken  from  pyloric  portion  of  stomach  of  rlojc  (luring  diKestion  of  mixed 
fofKl  (nUer  H<-rnar<l).  a,  (liHintf(frat«(i  niiisoiilar  fibers,  Ktriw  iiavinR  disapiH-ared  ;  /»,  r, 
muwMjIar  flix-rs  In  wiiloh  Ktrine  have  partly  disappeared  ;  d,  d,  d.  Kloliuies  of  fat ;  e.  e,  e, 
Ktareh  :  7.  molecular  f^ranules. 


350  ANIMAL  PHYSIOLOGY. 

become  peptone,  and  in  some  animals  fat  is  split  up  into  free 
fatty  acid  and  glycerine ;  but  the  digestion  of  fat  in  the  stom- 
ach is  very  limited  at  best,  and  probably  does  not  go  on  to 
emulsification  or  saponification.  The  digestion  of  starch  con- 
tinues in  the  stomach  until  the  reaction  of  the  food-mass  be- 
comes acid.  This  in  the  hog  may  not  be  far  from  one  to  two 
hours,  and  the  amylolytic  ferment  acts  with  great  rapidity  even 
without  the  body.  The  food  is  moved  about  to  a  certain  ex- 
tent, so  as  to  expose  every  part  freely  to  the  mucous  mem- 
brane and  its  secretions.  It  is  likely  that  the  sugar  resulting 
from  the  digestion  of  starch,  the  peptones,  and,  to  some  ex- 
tent, the  fat  formed  (if  any),  is  received  into  the  blood  from 
the  stomach. 

As  the  partially  digested  mass  (chyme)  is  passed  on  into  the 
intestine  as  a  result  of  the  action  of  the  alkaline  bile,  the  para- 
peptone,  pepsin,  and  bile-salts  are  deposited.  Certain  of  the 
constituents  of  digestion  are  thus  delayed,  a  portion  of  the  pep- 
sin is  probably  absorbed,  either  altered  or  unaltered,  and  pep- 
sin is  thus  got  rid  of,  making  the  way  clear,  so  to  speak,  for 
the  action  of  trypsin.  At  all  events,  digestion  in  one  part  of 
the  tract  is  antagonized  by  digestion  in  another,  but  we  must 
also  add  supplemented. 

The  fat,  which  had  been  but  little  altered,  is  emulsified  by 
the  joint  action  of  the  bile  and  pancreatic  secretion ;  a  portion 
is  saponified,  which  again  helps  in  emulsification,  while  an 
additional  part,  in  form  but  little  changed,  is  probably  dealt 
with  by  the  absorbents. 

Proteid  digestion  is  continued,  and,  besides  peptones,  ni- 
trogenous crystalline  bodies  are  formed  (leucin  and  tyrosin), 
but  under  what  conditions  or  to  what  extent  is  not  known ; 
though  the  quantity  is  likely  very  variable,  both  with  the  spe- 
cies of  animal  and  the  circumstances,  such  as  quantity  and 
quality  of  food ;  and  it  is  likely  also  dependent  not  a  little  on 
the  rate  of  absorption.  It  seems  altogether  probable  that  in 
those  that  use  an  excess  of  nitrogenous  food  more  of  these 
bodies  are  formed,  and  thus  give  an  additional  work  to  the  ex- 
creting organs,  including  the  liver.  But  the  absence  of  albu- 
min from  healthy  faeces  points  to  the  complete  digestion  of 
proteids  in  the  alimentary  canal.  Plainly  the  chief  work  of 
intestinal  digestion  is  begun  and  carried  on  in  the  upper  part 
of  the  tract,  where  the  ducts  of  the  main  glands  are  to  be 
found. 

The  contents  of  the  intestine  swarm  with  bacteria,  though 


DIGESTION   OF   FOOD.  357 

these  are  probably  kept  under  control  to  some  extent  by  the 
bile,  the  functions  of  which  as  an  antiseptic  we  have  already 
considered. 

The  removal  of  fats  by  the  villi  Avill  be  shortly  considered. 
The  other  products  of  digestion  probably  find  their  way  into 
the  general  circulation  by  the  portal  blood,  passing  through 
the  liver,  which  organ  modifies  some  of  them  in  ways  to  be 
examined  later. 

The  valvulcB  conniventes  greatly  increase  the  surface  of  the 
intestine,  and  retard  the  movements  of  the  partially  digested 
mass,  both  of  which  are  favorable.  The  peristaltic  movements 
of  the  small  gut  serve  the  obvious  purpose  of  moving  on  the 
digesting  mass,  thus  making  way  for  fresh  additions  of  chyme 
from  the  stomach,  and  carrying  on  the  more  elaborated  con- 
tents to  points  where  they  can  receive  fresh  attention,  both 
digestive  and  absorptive. 

Comparative. — In  man,  the  carnivora,  and  some  other  groups, 
it  is  likely  tliat  digestion  in  the  large  intestine  is  slight,  the 
work  being  mostly  completed — at  all  events,  so  far  as  the  action 
of  the  secretions  is  concerned — before  this  division  of  the  tract 
is  reached,  though  doubtless  absorption  goes  on  there  also. 
The  muscular  strength  of  this  gut  is  important  in  the  act  of 
defecation. 

But  the  great  size  of  the  large  intestine  in  ruminants — in 
the  horse,  etc, — together  with  the  bulky  character  of  the  food 
of  such  animals,  points  to  the  existence  of  possibly  extensive 
processes  of  which  we  are  ignorant.  It  is  generally  believed 
that  food  remains  but  a  short  time  in  the  stomach  of  the  horse, 
and  that  the  caecum  is  a  sort  of  reservoir  in  which  digestive 
processes  are  in  jjrogress,  and  also  for  water. 

Fermentations  go  on  in  the  intestine,  and  probably  among 
ruminants  they  are  numerous  and  essential,  though  our  actual 
knowledge  of  the  subject  is  very  limited. 

The  gases  found  in  the  human  stomach  are  atmospheric  air 
(swaHowed)  and  carbon  dioxide,  derived  from  the  blood.  Those 
of  tlie  intestine  are  nitrogen,  hydrogen,  carbonic  anhydride, 
sulphureted  hydrogen,  and  marsh-gas,  the  quantity  varying 
considerably  with  the  diet. 

Pathological. — In  subjects  of  a  highly  neurotic  temperament 
and  unstable  nervous  system  it  sometimes  happens  that  im- 
mense quantities  of  gas  are  belched  from  an  empty  stomach  or 
distend  tlut  intestines. 

It  is  known  that  the  oxygen  swallowed  is  absorbed  into  the 


358  ANIMAL  PHYSIOLOGY. 

blood,  and  the  carbonic  anhydride  found  in  the  stomach  de- 
rived from  that  fluid. 

It  will  thus  be  seen  that  the  alimentary  tract  has  not  lost 
its  respiratory  functions  even  in  man,  and  that  these  may  in 
certain  instances  be  inordinately  developed  (reversion). 

Special  Considerations. 

It  is  a  matter  well  recognized  by  those  of  much  experience 
in  breeding  and  keeping  animals  with  restricted  freedom  and 
under  other  conditions  differing  widely  from  the  natural  ones 
— i.  e..  those  under  which  the  animals  exist  in  a  wild  state — that 
the  nature  of  the  food  must  vary  from  that  which  the  untamed 
ancestors  of  our  domestic  animals  used.  Food  may  often  with 
advantage  be  cooked  for  the  tame  and  confined  animal.  The 
digestive  and  the  assimilative  powers  have  varied  with  other 
changes  in  the  organism  brought  about  by  the  new  surround- 
ings. So  much  is  this  the  case,  that  it  is  necessary  to  resort  to 
common  experience  and  to  more  exact  experiments  to  ascertain 
the  best  methods  of  feeding  animals  for  fattening,  for  work, 
or  for  breeding.  Inferences  drawn  from  the  feeding  habits  of 
wild  animals  allied  to  the  tame  to  be  valuable  must  always, 
before  being  applied  to  the  latter,  be  subjected  to  correction 
by  the  results  of  experience. 

To  a  still  greater  degree  does  this  apply  to  man  himself. 
The  greater  his  advances  in  civilization,  the  more  he  departs 
from  primitive  habits  in  other  respects,  the  more  must  he  de- 
part in  his  feeding.  With  the  progressive  development  of 
man's  cerebrum,  the  keener  struggle  for  place  and  power,  the 
more  his  nervous  energies  are  diverted  from  the  lower  func- 
tions of  digestion  and  assimilation  of  food ;  hence  the  greater 
need  that  food  shall  be  more  carefully  selected,  and  more 
thoroughly  and  scientifically  prepared.  Not  only  so,  but,  with 
our  increasing  refinement,  the  progress  of  digestion  to  suc- 
cessful issues  demands  that  the  senses  of  man  be  ministered 
to  in  order  that  there  be  no  interferences  in  the  central  nerv- 
ous system,  on  the  one  hand,  and  every  encouragement  to  the 
latter  to  furnish  the  necessary  nervous  impulses  to  the  digest- 
ive organs  and  the  tissues  in  every  part  of  the  organism :  for 
it  is  not  enough  that  food  be  digested  in  the  ordinary  sense ; 
it  must  also  be  built  up  into  the  tissues,  a  process  depending, 
as  we  shall  endeavor  to  show  later,  on  the  nervous  system. 

The  "  gastronomic  art "  has,  therefore,  become  of  great  im- 


DIGESTION  OP   POOD.  359 

portance.  It  is  as  yet  more  of  an  art  than  a  science ;  the  cook 
has  outstripped  the  physiologist,  if  not  the  chemist  also,  in  this 
direction. 

We  can  not  explain  fully  why  food  prepared  by  certain 
methods  and  served  in  courses  of  a  certain  established  order  is 
so  suited  to  refined  man.  A  part  is  known,  but  a  great  deal 
remains  to  be  discovered.  We  may,  however,  notice  a  few 
points  of  importance  in  regard  to  the  preparation  of  food. 

It  is  now  well  established  by  experience  that  animals  kept 
in  confinement  must  have,  in  order  to  escape  disease  and  attain 
the  best  results  on  the  whole,  a  diet  which  not  only  imitates 
that  of  the  corresponding  wild  forms  generally,  but  even  in 
details,  with,  it  may  be,  altered  proportions  or  added  constitu- 
ents, in  consequence  of  the  diflierence  in  the  environment.  To 
illustrate :  poultry  can  not  be  kept  healthy  confined  in  a  shed 
without  sand,  gravel,  old  mortar,  or  some  similar  preparation ; 
and  for  the  best  results  they  must  have  green  food  also,  as 
lettuce,  cabbage,  chopped  green  clover,  grass,  etc.  They  must 
not  be  provided  with  as  much  food  as  if  they  had  the  exercise 
afforded  by  running  hither  and  thither  over  a  large  field.  We 
have  chosen  this  case  because  it  is  not  commonly  recognized 
that  our  domesticated  birds  have  been  so  modified  that  special 
study  must  be  made  of  the  environment  in  all  cases  if  they 
are  not  to  degenerate.  The  facts  in  regard  to  horned  cattle, 
horses,  and  dogs  are  perhaps  better  known. 

But  all  these  instances  are  simple  as  compared  with  man. 
The  lower  mammals  can  live  and  flourish  with  comparatively 
little  change  of  diet ;  not  so  man.  He  demands  diet  not  only 
dissimilar  in  its  actual  grosser  nature,  but  differently  prepared. 
In  a  word,  for  the  efferent  nervous  impulses,  on  which  the 
digestive  processes  depend  to  be  properly  supplied,  it  has  be- 
come necessary  that  a  variety  of  afferent  impulses  (through 
eye,  ear,  nose,  palate)  reach  the  nervous  centers,  attuning  them 
to  harmony,  so  that  they  shall  act,  yet  not  interfere  with  one 
anoth(;r. 

Cooking  greatly  alters  the  chemical  composition,  the  me- 
chanical condition,  and,  in  consequence,  the  flavor,  the  digesti- 
bility, and  tlio  nutritive  value  of  foods.  To  illustrate:  meat  in 
its  raw  condition  would  present  mechanical  difficulties,  the  di- 
gestive fluids  permeating  it  less  completely;  an  obstach;,  how- 
cvftr,  of  far  greater  magnitude  in  the  case  of  most  vegetable 
foods.  By  cooking,  certain  chemical  compounds  are  replaced 
by  others,  while  some;  may  be  wholly   removed.     As  a  rule, 


360  ANIMAL  PHYSIOLOGY. 

boiling  is  not  a  good  form  of  preparing  meat,  because  it  with- 
draws not  only  salts  of  importance,  but  proteids  and  the  ex- 
tractives— nitrogenous  and  other.  Beef -tea  is  valuable  chiefly 
because  of  these  extractives,  though  it  also  contains  a  little 
gelatine,  albumin,  and  fats.  Salt  meat  furnishes  less  nutri- 
ment, a  large  part  having  been  removed  by  the  brine ;  not- 
withstanding, all  persons  at  times,  and  some  frequently,  find 
such  food  highly  beneficial,  the  efi^ect  being  doubtless  not  con- 
fined to  the  alimentary  tract. 

Meat,  according  to  the  heat  employed,  may  be  so  cooked  as 
to  retain  the  greater  part  of  its  juices  within  it  or  the  reverse. 
With  a  high  temperature  (65°  to  70°  C.)  the  outside  in  roasting 
may  be  so  quickly  hardened  as  to  retain  the  juices. 

In  feeding  dogs  it  is  both  physiological  and  economical  to 
give  the  animal  the  broth  as  well  as  the  meat  itself.  The  poor 
man  may  get  excellent  food  cheaply  by  using  not  alone  the 
meat  of  the  shank  of  beef,  but  the  extractives  derived  from  it. 
There  is  much  waste  not  only  by  the  consumption  of  more  food 
than  is  necessary,  but  by  the  purchase  of  kinds  in  which  that 
important  class  of  bodies,  the  proteids,  comes  at  too  high  a 
price. 

It  is  remarkable  in  the  highest  degree  that  man's  appetite, 
or  the  instinctive  choice  of  food,  has  proved  wiser  than  our 
science.  It  would  be  impossible  even  yet  to  match,  by  calcula- 
tions based  on  any  data  we  can  obtain,  a  diet  for  each  man  equal 
upon  the  whole  to  what  his  instincts  prompt.  With  the  lower 
mammals  we  can  prescribe  with  greater  success.  At  the  same 
time  chemical  and  physiological  science  can  lay  down  general 
principles  based  on  actual  experience,  which  may  serve  to  cor- 
rect some  artificialities  acquired  by  perseverance  in  habits  that 
were  not  based  on  the  true  instincts  of  a  sound  body  and  a 
healthy  mental  and  moral  nature;  for  the  influence  of  the 
latter  can  not  be  safely  ignored  even  in  such  discussions  as  the 
present.  These  remarks,  however,  are  meant  to  be  suggestive 
rather  than  exhaustive. 

We  may  with  advantage  inquire  into  the  nature  of  hunger 
and  thirst.  These,  as  we  know,  are  safe  guides  usually  in  eat- 
ing and  drinking. 

After  a  long  walk  on  a  warm  day  one  feels  thirsty,  the 
mouth  is  usually  dry ;  at  all  events,  moistening  the  mouth, 
especially  the  back  of  it  (pharynx),  will  of  itself  partially  re- 
lieve thirst.  But  if  we  remain  quiet  for  a  little  time  the  thirst 
grows  less,  even  if  no  fluid  be  taken.     The  dryness  has  been 


DIGESTION  OP   FOOD.  ^  361 

relieved  by  the  natural  secretions.  If,  however,  fluid  be  intro- 
duced into  the  blood  either  directly  or  through  the  alimentary 
canal,  the  thirst  is  also  relieved  speedily.  The  fact  that  we 
know  when  to  stop  drinking  water  shows  of  itself  that  there 
must  be  local  sensations  that  guide  us,  for  it  is  not  possible  to 
believe  that  the  whole  of  the  fluid  taken  can  at  once  have  en- 
tered the  blood. 

Again,  in  the  case  of  hunger,  the  introduction  of  innutritions 
matters,  as  earth  or  sawdust,  will  somewhat  relieve  the  urgent 
sensations  in  extreme  cases ;  as  will  also  the  use  of  tobacco  by 
smokers,  or  much  mental  occupation,  though  the  latter  is 
rather  illustrative  of  the  lessening  of  the  consciousness  of  the 
ingoing  impulses  by  diverting  the  attention  from  them.  But 
hunger,  like  thirst,  may  be  mitigated  by  injections  into  the 
intestines  or  the  blood.  It  is,  therefore,  clear  that,  while  in  the 
case  of  hunger  and  thirst  there  is  a  local  expression  of  a  need, 
a  peculiar  sensation,  more  pronounced  in  certain  parts  (the 
fauces  in  the  case  of  thirst,  the  stomach  in  that  of  hunger), 
yet  these  may  be  appeased  from  within  through  the  medium 
of  the  blood,  as  well  as  from  without  by  the  contact  of  food  or 
water,  as  the  case  may  be. 

Up  to  the  present  we  have  assumed  that  the  changes 
wrought  in  the  food  in  the  alimentary  tract  were  identical 
with  those  produced  by  the  digestive  ferments  as  obtained  by 
extracts  of  the  organs  naturally  producing  them.  But  for 
many  reasons  it  seems  probable  that  artificial  digestion  can  not 
be  regarded  as  parallel  with  the  natural  processes  except  in  a 
very  general  way.  When  we  take  into  account  the  absence  of 
muscular  movements,  regulated  according  to  no  rigid  prin- 
ciples, but  varying  with  innumerable  circumstances  in  all 
probability ;  the  absence  of  the  influence  of  the  nervous  sys- 
tem determining  the  variations  in  the  quantity  and  compo- 
sition of  the  outflow  of  the  secretions ;  the  changes  in  the  rate 
of  so-called  absorption,  which  doubtless  influences  also  the  act 
of  the  secretion  of  the  juices — by  these  and  a  host  of  other  con- 
siderations we  are  lead  to  hesitate  before  we  commit  ourselves 
too  unreservedly  to  the  belief  that  the  processes  of  natural 
'ligestion  can  be  exactly  imitated  in  the  laboratory. 

What  is  it  which  enables  one  man  to  digest  hal)itually  what 
may  be  almost  a  poison  to  another  ?  How  is  it  that  each  one 
can  dispo.se  readily  of  a  food  at  one  time  that  at  another  is  quite 
iiidigesti}>le  ?  To  reply  tliat,  in  the  one  case,  the  digestive 
fluids  are  poured  out  and   in  the  other  not,  is  to  go  little  below 


362  ,         ANIMAL   PHYSIOLOGY. 

the  surface,  for  one  asks  the  reason  of  this,  if  it  be  a  fact,  as  it 
no  doubt  is.  When  we  look  further  into  the  peculiarities  of 
digestion,  etc.,  we  recognize  the  influence  of  race  as  such,  and 
in  the  race  and  the  individual  that  obtrusive  though  ill-under- 
stood fact — the  force  of  habit,  operative  here  as  elsewhere. 
And  there  can  be  little  doubt  that  the  habits  of  a  people,  as  to 
food  eaten  and  digestive  peculiarities  established,  become  or- 
ganized, fixed,  and  transmitted  to  posterity. 

It  is  probably  in  this  way  that,  in  the  course  of  the  evolu- 
tion of  the  various  groups  of  animals,  they  have  come  to  vary 
so  much  in  their  choice  of  diet  and  in  their  digestive  processes, 
did  we  but  know  them  thoroughly  as  they  are ;  for  to  assume 
that  even  the  digestion  of  mammals  can  be  summed  up  in  the 
simple  way  now  prevalent  seems  to  us  too  broad  an  assump- 
tion.   The  field  is  very  wide,  and  as  yet  but  little  explored. 

Human  Physiology. — The  study  of  Alexis  St.  Martin  has  fur- 
nished probably  the  best  example  of  genuine  human  physiology 
to  be  found,  and  has  yielded  a  harvest  rich  in  results. 

We  suggest  to  the  student  that  self-observation,  without 
interfering  with  the  natural  processes,  may  lead  to  valuable 
knowledge ;  for,  though  it  may  lack  some  of  the  precision  of 
laboratory  experiments,  it  will  prove  in  many  respects  more 
instructive,  suggestive,  and  impressive,  and  have  a  bearing  on 
medical  practice  that  will  make  it  telling.  Not  that  we  would 
be  understood  now  or  at  any  time  as  depreciating  laboratory 
experiments ;  but  we  wish  to  point  out  from  time  to  time  how 
much  may  be  learned  in  ways  that  are  simple,  inexpensive, 
and  consume  but  little  time. 

The  latu  of  rhythm  is  illustrated,  both  in  health  and  disease, 
in  striking  ways  in  the  digestive  tract.  An  individual  long 
accustomed  to  eat  at  a  certain  hour  of  the  day  will  experience 
at  that  time  not  only  hunger,  but  other  sensations,  probably 
referable  to  secretion  of  a  certain  quantity  of  the  digestive 
juices  and  to  the  movements  that  usually  accompany  the  pres- 
ence of  food  in  the  alimentary  tract.  Some  persons  find  their 
digestion  disordered  by  a  change  in  the  hours  of  meals. 

It  is  well  known  that  defecation  at  periods  fixed,  even  within 
a  few  minutes,  has  become  an  established  habit  with  hosts  of 
people ;  and  the  same  is  to  a  degree  true  of  dogs,  etc.,  kept  in 
confinement,  that  are  taught  cleanly  habits,  and  encouraged 
therein  by  regular  attention  to  their  needs. 

Now  and  then  a  case  of  what  is  very  similar  to  regurgita- 
tion of  food  in  ruminants  is  to  be  found  among  human  beings. 


DIGESTION    OF    FOOD.  3(33 

This  is  traceable  to  habit,  which  is  bound  up  with  the  law  of 
rhythm  or  periodic  increased  and  diminished  activity. 

Indeed,  every  one  sufficiently  observant  may  notice  in  him- 
self instances  of  the  application  of  this  law  in  the  economy  of 
his  own  digestive  organs. 

This  tendency  is  imjiortant  in  preserving  energy  for  higher 
ends,  for  such  is  the  result  of  the  operation  of  this  law  every- 
where. 

The  law  of  correlation,  or  mutual  dependence,  is  well  illus- 
trated in  the  series  of  organs  composing  the  alimentary  tract. 

The  condition  of  the  stomach  has  its  counterpart  in  the  rest 
of  the  tract :  thus,  when  St.  Martin  had  a  disordered  stomach, 
the  epithelium  of  his  tongue  showed  corresponding  changes. 

We  have  already  referred  to  the  fact  that  one  part  may  do 
extra  work  to  make  up  for  the  deficiencies  of  another. 

It  is  confidently  asserted  of  late  that,  in  the  case  of  persons 
long  unable  to  take  food  by  the  mouth,  nutritive  substances 
given  by  enemata  find  their  way  up  to  the  duodenum  by  anti- 
peristalsis.  Here,  then,  is  an  example  of  an  acquired  adaptive 
arrangement  under  the  stress  of  circumstances. 

It  can  not  be  too  much  impressed  on  the  mind  that  in  the 
complicated  body  of  the  mammal  the  work  of  any  one  organ 
is  constantly  varying  with  the  changes  elsewhere.  It  is  this 
mutual  dependence  and  adaptation — an  old  doctrine,  too  much 
left  out  of  sight  in  modern  physiology — which  makes  the  at- 
tempt to  coinpleiely  unravel  vital  processes  well-nigh  hopeless; 
though  each  accumulating  true  observation  gives  a  Ijetter  in- 
sight into  this  kaleidoscopic  mechanism. 

We  have  not  attempted  to  make  any  statements  as  to  the 
quantity  of  the  various  secretions  discharged.  This  is  large, 
douljtless,  but  much  is  prol)ably  reabsorbed,  either  altered  or 
unaltered,  and  used  over  again.  In  the  case  of  fistulm  the  con- 
ditions are  so  unnatural  that  any  conclusions  as  to  the  normal 
quantity  from  tlie  data  tliey  afford  must  be  liighly  unsatisfac- 
tory. Moreover,  the  quantity  must  be  very  variable,  accord- 
ing to  th(?  law  we  are  now  considering.  It  is  well  known  that 
dry  ffjod  pr(;v(jkes  a  more  abundant  discharge  of  saliva,  and 
this  is  doubtless  but  one  example  of  many  other  relations  be- 
tween the  cliaractf-r  of  the  food  and  the  quantity  of  secretion 
provided. 

Evolution. — We  have  from  time  to  time  eitlier  distinctly 
point(;d  out  or  hinted  at  the  evolutionary  implications  of  tlio 
facts  of  this  department  of  physiology.     The  structure  of  the 


3^4  ANIMAL   PHYSIOLOGY. 

digestive  organs,  plainly  indicating  a  rising  scale  of  complexity 
with  greater  and  greater  differentiation  of  function,  is,  beyond 
question,  an  evidence  of  evolution. 

The  law  of  natural  selection  and  the  law  of  adaptation, 
giving  rise  to  new  forms,  have  both  operated,  we  may  believe, 
from  what  can  be  observed  going  on  around  us  and  in  our- 
selves. The  occurrence  of  transitional  forms,  as  in  the  epi- 
thelium of  the  digestive  tract  of  the  frog,  is  also  in  harmony 
with  the  conception  of  a  progressive  evolution  of  structure 
and  function.  But  the  limits  of  space  will  not  permit  of  the 
enumeration  of  details. 

Summary. — A  very  brief  resume  of  the  subject  of  digestion 
will  probably  suffice. 

Food  is  either  organic  or  inorganic  and  comprises  proteids, 
fats,  carbohydrates,  salts,  and  water ;  and  each  of  these  must 
enter  into  the  diet  of  all  known  animals.  They  must  also  be 
in  a  form  that  is  digestible.  Digestion  is  the  reduction  of  food 
to  a  form  such  that  it  may  be  further  dealt  with  by  the  aliment- 
ary tract  prior  to  being  introduced  into  the  blood  (absorption). 
This  is  effected  in  different  parts  of  the  tract,  the  various  con- 
stituents of  food  being  differently  modified,  according  to  the 
secretions  there  provided,  etc.  The  digestive  juices  contain 
essentially  ferments  which  act  only  under  definite  conditions  of 
chemical  reaction,  temperature,  etc. 

The  changes  wrought  in  the  food  are  the  following :  starches 
are  converted  into  sugars,  proteids  into  peptones,  and  fats  into 
fatty  acids,  soaps,  and  emulsion ;  which  alterations  are  effected 
by  ptyalin  and  amylopsin,  pepsin  and  trypsin,  and  bile  and 
pancreatic  steapsin,  respectively. 

Outside  the  mucous  membrane  containing  the  glands  are 
muscular  coats,  serving  to  bring  about  the  movements  of  the 
food  along  the  digestive  tract  and  to  expel  the  faeces,  the  circu- 
lar fibers  being  the  more  important.  These  movements  and  the 
processes  of  secretion  and  so-called  absorption  are  under  the 
control  of  the  nervous  system. 

The  preparation  of  the  digestive  secretions  involves  a  series 
of  changes  in  the  epithelial  cells  concerned,  which  can  be  dis- 
tinctly traced,  and  take  place  in  response  to  nervous  stimula- 
tion. 

These  we  regard  as  inseparably  bound  up  with  the  healthy 
life  of  the  cell.     To  be  natural,  it  must  secrete. 

The  blood-vessels  of  the  stomach  and  intestine  and  the  villi 
of  the  latter  receive  the  digested  food  for  further  elaboration 


THE   KESPIKATORY   SYSTEM. 


365 


(absorption).  The  undigested  remnant  of  food  and  the  excre- 
tions of  the  intestine  make  up  the  faeces,  the  latter  being  ex- 
pelled by  a  series  of  co-ordinated  muscular  movements  essen- 
tially reflex  in  origin. 


THE  RESPIRATORY  SYSTEM. 

In  the  mammal  the  breathing  organs  are  lodged  in  a  closed 
cavity,  separated  by  a  muscular  partition  from  that  in  which 
the  digestive  and  certain  other  organs   are  contained.     This 


FlO.  ifl^T).  -LuriKH,  anU-rior  vnw  iSapix-i).  1,  upper  lohr  of  left  lungf;  2,  lower  lobo;  :i.  fissure; 
4,  notch  corrfrHfKiridinK  t^>  afx-x  of  heart  ;  T>,  pericardium  ;  (!.  ujjper  lobe  of  rlKht  liine  ;  7, 
middle  lol»e  :  H.  lower  lof>e  ;  !l.  flBHiire  ;  10,  fissure  ;  11,  diaphraKin  ;  12,  anterior  mediasti- 
num ;  13,  thyroid  xlaiid  ;  M,  middle  cervical  aponeurosis  ;  If),  process  i>t  attachment  of 
mediastinum  to  pericardium  :  1<5,  16,  seventh  ribs ;  17,  17,  tranaversales  muscles  ;  IH,  linea 
alba. 


366 


ANIMAL  PHYSIOLOGY. 


thoracic  cliainher  may  be  said  to  be  reserved  for  circulatory 
and  respiratory  organs  which,  we  again  point  out,  are  so  related 
that  they  really  form  parts  of  one  system. 

The  mammal's  blood  requires  so  much  aeration  (ventilation) 
that  the  lungs  are  very  large  and  the  respiratory  system  has 
become  greatly  specialized.  We  no  longer  find  the  skin  or  ali- 
mentary canal  taking  any  large  share  in  the  process ;  and  the 
lungs  and  the  mechanisms  by  which  they  are  made  to  move  the 
gases  with  which  the  blood  and  tissues  are  concerned  become 
very  complicated. 


Fig.  296.— Bronchia  and  lungs,  posterior  view  (Sappey).  1,1,  summit  of  lungs  ;  2,  2,  base  of 
lungs ;  3,  trachea  ;  4,  right  bronchus  ;  5,  division  to  upper  lobe  of  lung  :  6,  division  to 
lower  lobe  ;  7,  left  bronchus  ;  8,  division  to  upper  lobe  ;  9,  division  to  lower  lobe  ;  10,  left 
branch  of  pulmonary  artery  ;  11,  right  branch  ;  12,  left  auricle  of  heart ;  13,  left  superior 
pulmonary  vein  ;  14,  left  inferior  pulmonary  vein  ;  15.  right  superior  pulmonary  vein  ;  16, 
right  inferior  pulmonary  vein  ;  17,  inferior  vena  cava  :  18.  left  ventricle  of  heart ;  19,  right 
ventricle. 


Our  studies  of  muscle  physiology  should  have  made  clear 
the  fact  that  tissue-life  implies  the  constant  consumption  of 
oxygen  and  discharge  of  carbonic  anhydride,  and  that  the  pro- 
cesses which  give  rise  to  this  are  going  on  at  a  rapid  rate ;  so 
that  the  demands  of  the  animal  for  oxygen  constantly  may  be 
readily  understood  if  one  assumes,  what  can  be  shown,  though 
less  readily  than  in  the  case  of  muscle,  that  all  the  tissues  are 
constantly  craving,  as  it  were,  for  this  essential  oxygen — well 
called  "  vital  air." 


THE  RESPIRATORY  SYSTEM, 


367 


Respiration  may,  then,  be  regarded  from  a  physical   and 
chemical  point  of  view,  though  in  this  as  in  other  instances  we 


Fig.  297.— Trachea  and  branchial  tubes  (Sappey).  1,  2,  larynx  ;  3,  3,  trachea  ;  4.  bifurcation 
of  trachea  :  :>.  rifcht  bronchus  ;  G.  left  bronchus  ;  7,  bronchial  division  to  upper  lobe  or 
right  lunK  ;  H.  division  to  middle  lobe  ;  9,  division  to  lower  lobe  ;  10.  division  to  upper  lobe 
of  left  XnuK  :  11.  division  to  lower  lobe  ;  12,  12,  12,  12,  ultimate  ramifications  of  bronchia; 
13.  13.  13.  13,  luntfs.  represented  in  contour  ;  14,  14,  summit  of  lungs  ;  15,  15,  base  of  lungs. 

must  be  on  our  guard  against  regarding  physiological  processes 
as  ever  purely  j^hysical  or  purely  chemical.  The  respiratory 
{irocess  in  the  mammal,  unlike  the  frog,  consists  of  an  active 
and  a  (largely)  passive  phase.  The  air  is  not  pumped  into  the 
lungs,  but  sucked  in.  So  great  is  the  complexity  of  the  lungs 
in  the  mammal,  that  the  frog's  lung  (whicli  may  be  rcsadily 
understood  by  blowing  it  up  by  inserting  a  small  pipe  in  the 
glottic  opf;ning  of  the  animal  and  then  ligaturing  the  distended 
organ)  may  be  c;ompared  to  a  single  infundibulum  of  the  mam- 
malian lung. 

AsHuniing  that  the  student  is  somewhat  conversant  with  the 


368  ANIMAL   PHYSIOLOGY. 

coarse  and  fine  anatomy  of  the  respiratory  organs,  we  call  at- 
tention to  the  physiological  aspects  of  some  points.  The  lungs 
represent  a  membranous  expansion  of  great  extent,  lined  with 
flattened  cells  and  supporting  innumerable  capillary  blood-ves- 
sels. The  air  is  admitted  to  the  complicated  foldings  of  this 
membrane  by  tubes  which  remain,  throughout  the  greater  part 
of  their  extent,  open,  being  composed  of  cartilaginous  rings, 
completed  by  soft  tissues,  of  which  plain  muscle-cells  form  an 


Fig.  298.— Mold  of  a  terminal  bronchus  and  a  group  of  air-cells  moderately  distended  by- 
injection,  from  the  human  subject  (Robin). 

important  part,  serving  to  maintain  a  tonic  resistance  against 
pulmonary  and  bronchial  pressure,  as  well  as  serving  to  aid 
in  the  act  of  coughing,  etc.,  so  important  in  expelling  foreign 
bodies  or  preventing  their  ingress. 

The  bronchial  tubes  are  lined  with  a  mucous  membrane, 
kept  moist  by  the  secretions  of  its  glands,  and  covered  with 
ciliated  epithelium,  as  are  also  the  nasal  passages,  which  by 
the  outward  currents  they  create,  favor  diffusion  of  gases,  and 
removal  of  excess  of  mucus.  The  thoracic  walls  and  the  lungs 
themselves  are  covered  with  a  tough  but  thin  membrane  lined 
with  flattened  cells,  which  secrete  a  small  quantity  of  fluid. 


THE  RESPIRATORY  SYSTEM. 


369 


that  serves  to  maintain  the  surrounding  parts  in  a  moist  con- 
dition, thus  lessening  friction.     The   importance  of  this  ar- 


FiG.  299.— Section  of  the  parenchyma  of  the  human  lung.  Injected  through  the  pulmonary- 
artery  (Schulze).    a,  a,  c,  c,  walls  of  the  air-cells  ;  6,  small  arterial  branch. 

rangement  is  well  seen  when,  in  consequence  of  inflammation 
of  this  pleura,  it  becomes  dry,  giving  rise  during  each  respira- 
tory movement  to  a  friction-sound  and  a  painful  sensation. 
It  will  not  be  forgotten  that  this  membrane  extends  over  the 
diai)hragm,  and  that,  in  consequence  of  the  lungs  completely 
filling  all  the  space  (not  occupied  by  other  organs)  during  every 
position  of  the  chest- walls,  the  costal  and  pulmonary  pleural 
surfaces  are  in  constant  contact.  By  far  the  greater  part  of 
the  lung-substance  consists  of  elastic  tissue,  thus  adapting  the 
principal  respiratory  organs  to  that  amount  of  distention  and 
recoil  to  which  they  are  ceaselessly  subjected  during  the  en- 
tire lif(;time  of  the  animal. 


The  Entrance  and  Exit  of  Air. 

Since  the  lungs  fill  uj)  so  completely  the  thoracic  cavity, 
manifestly  any  change  in  the  size  of  the  latter  must  lead  to 
an  increase  or  diminuticjn  in  the  quantity  of  air  they  contain. 
Since  the  air  within  the  respiratory  organs  is  being  constantly 

24 


370 


ANIMAL  PHYSIOLOGY. 


robbed  of  its  oxygen,  and  rendered  impure  by  the  addition  of 
carbonic  dioxide,  the  former  must  be  renewed  and  the  latter 

expelled ;  and,  as  mere  diffu- 
sion takes  place  too  slowly  to 
accomplish  this  in  the  mam- 
mal, this  process  is  assisted 
by  the  nervous  system  set- 
ting certain  muscles  at  work 
to  alter  the  size  of  the  chest 
cavity.  Because  of  the  ribs 
being  placed  obliquely,  it  fol- 
lows that  their  elevation  will 
result  in  the  enlargement  of 
the  thoracic  cavity  in  the  an- 
tero-posterior  diameter ;  and, 
as  the  chest,  in  consequence, 
gets  wider  from  above  down- 
ward, also  in  the  transverse 
diameter  ;  which  is  more- 
over assisted  by  the  eversion 
of  the  lower  borders  of  the 
ribs ;  and,  if  the  convexity  of 
the  diaphragm  were  dimin- 
ished by  its  contraction  and 
consequent  descent,  it  would  follow  that  the  chest  would  be  in- 
creased in  the  vertical  diameter  also.  All  these  events,  favor- 
able to  the  entrance  of  air,  actually  take  place  through  agencies 
we  must  now  consider.  The  student  is  recommended  to  look 
into  the  insertion,  etc.,  of  the  muscles  concerned,  to  which  we 
can  only  briefly  refer. 

The  act  of  inspiration  commences  by  the  fixation  of  the 
uppermost  ribs,  beginning  with  the  first  two,  by  means  of  the 
scaleni  muscles,  this  act  being  followed  up  by  the  contraction 
of  the  external  intercostals,  leading  to  the  elevation  of  the 
other  ribs ;  at  the  same  time,  the  arch  of  the  diaphragm  de- 
scends in  consequence  of  the  contraction  of  its  various  mus- 
cular bundles.  Under  these  circumstances,  the  air  from  with- 
out must  rush  in,  or  a  vacuum  be  formed  in  the  thoracic 
cavity ;  and,  since  there  is  free  access  for  the  air  through  the 
glottic  opening,  the  lungs  are  of  necessity  expanded.  This  in- 
going air  has  had  to  overcome  the  elastic  resistance  of  the 
lungs,  which  amounts  to  about  5  millimetres  of  mercury  in 
man,  as  ascertained  by  tying  a  manometer  in  the  windpipe  of 


Fig.  300.— Dia,s:ram  illustrating  elevation  of  ribs 
in  inspiration  (Beclard).  Tlie  dark  lines  rep- 
resent the  ribs,  sternum,  and  costal  cartilages 
in  inspiration. 


THE   RESPIRATORY  SYSTEM. 


371 


a  dead  subject,  and  then  opening  the  thorax  to  equalize  the 
inside  and  outside  pressures,  when  the  lungs  at  once  collapse 
and  the  manometer  shows  a 
rise  of  the  mercury  to  the  ex- 
tent indicated  above.  To  this 
we  must  add  the  influence  of 
the  tonic  contraction  of  the 
bronchial  muscles  before  re- 
ferred to,  though  this  is  prob- 
ably not  very  great. 

That  there  are  variations 
of  intrapulmonary  pressure 
may  be  ascertained  by  con- 
necting a  manometer  with  one 
nostril — the  other  being  closed 
— or  with  the  windpipe.  The 
mercury  shows  a  negative 
pressure  with  each  inspirato- 
ry, and  a  positive  with  each 
expiratory  act.  This  may 
amount  to  from  30  to  70  mil- 
limetres with  strong  inspira- 
tion, and  60  to  100  in  forcible 
expiration. 

When  inspiration  ceases,  the  elastic  recoil  of  the  rib  carti- 
lages and  the  ribs  themselves,  and  of  the  sternum,  the  weight 


Fig.  301.  —  Diagrammatic  representation  of 
action  of  diaphragm  in  inspiration  (Her- 
mann). Vertical  section  tiirough  second 
rib  on  right  side.  The  broken  and  dotted 
lines  show  the  amount  of  the  descent  of  the 
diaphragm  in  ordinary  and  in  deep  inspira- 
tion. 


Fio.  302.— Apparatus  U>  illustrat/-  relations  of  intraf horacic  and  external  pressures  (after 
H»-aunis).  A  glans  liell-iar  is  jirovidcd  with  a  liK'lii  slopi.cr,  through  vvhi<,'li  i)ns.scKa  branch- 
ing glaH.H  tube  (ltt>-d  with  a  pair  of  elastii;  l)agH  ri-pr<'scriliiig  luiig.M.  Tlic  bottom  of  the  jiii'  i.s 
flowed  \iy  rubber  membrane  n-preHentiiig  diaphragm.  A  mercMt\'  iriiiiiomctiT  iiidi('ate,s 
the  diff>T<-iii;e  in  prfssure  within  and  without  tlie  Iw^ll-Jar.  In  Iffi-lmml  figure  it  will  be 
Heen  that  thew;  pr<;HKureH  are  e<]iiiil  ;  in  right  (irmpirationi,  tlie  e.vtcriiiil  pn-ssurf  iH  cntj.sid- 
•rably  greater.  At  one  part  (>>)  an  elaHtic  m<!mbran(!  fills  a  hole  in  jar,  representing  an 
inU:rc;(.fHtul  Hpace. 


372 


ANIMAL  PHYSIOLOGY. 


Fig.  303. — ^Dorsal  view  of  four  vertebrae 
and  three  attached  ribs,  showing 
attachment  of  elevator  muscles  of 
ribs  and  intercostals  (after  Allen 
Thomsoni).  1,  long  and  short  eleva- 
tors ;  2,  external  intercostal ;  3,  in- 
ternal intercostal. 


of  these  parts  and  tliat  of  the  attached  muscles,  etc.,  assists  in 
the  return  of  the  chest  to  its  original  position,  entirely  indepen- 
dently of  the  action  of  muscles. 
Moreover,  with  the  descent  of  the 
diaphragm  the  abdominal  viscera 
have  been  thrust  down  and  com- 
pressed together  with  their  included 
gases ;  when  this  muscle  relaxes, 
they  naturally  exert  an  upward 
pressure.  Putting  these  events 
together,  it  is  not  difficult  to  un- 
derstand why  the  air  should  be 
squeezed  out  of  the  lungs,  the  elas- 
ticity of  which  latter  is,  as  we  have 
shown,  an  important  factor  in  itself. 
The  Muscles  of  Respiration. — The 
diaphragyn  may  be  considered  the 
most  important  single  respiratory 
muscle,  and  can  of  itself  maintain 
respiration.  The  scalejii  are  important  as  fixators  of  the  ribs; 
the  levatores  costarum,  and  external  intercostals,  as  normal  ele- 
vators. The  quadratus  lumborum 
assists  the  diaphragm  by  fixing  the 
last  rib.  These,  with  the  serratus 
porticus  superior,  may  be  regarded 
as  the  principal  muscles  called  into 
action  in  an  ordinary  inspiration. 
The  muscles  used  in  an  ordinary  ex- 
piratory act  are  the  internal  intercos- 
tals, the  iriangidaris  sterni,  and  ser- 
ratus posticus  inferior.  In  forced 
inspiration  the  lower  ribs  are  drawn 
down  and  retracted,  giving  support 
in  their  fixed  position  to  the  dia- 
phragm. The  scaleni,  pectorales, 
serratus  magnus,  latissimus  dorsi, 
and  others  are  called  into  action ;  but 
when  dyspnoea  becomes  extreme,  as 
in  one  with  a  fit  of  asthma,  nearly  all 
the  muscles  of  the  body  may  be  called 
into  play,  even  the  muscles  of  the 
face,  which  are  not  normally  active  at  all  or  but  very  slightly 
in  natural  breathing. 


Fig.  304.— Laryngoscopic  views  of 
the  glottis,  etc.  (after  Quain  and 
Czermak).  I.  Larynx  in  quiet 
breathing.  II.  During  a  deep  in- 
spiration. In  this  case  the  rings 
of  the  trachea  and  commence- 
mentof bronchiarevisible.  Such 
a  condition  is  persistent  in  many 
forms  of  disease  in  which  respir- 
ation is  attended  with  difficulty. 


THE   RESPIRATORY  SYSTEM.  373 

Facial  and  laryngeal  respiration  is  best  seen  in  sucli  animals 
as  tlie  rabbit,  and  it  is  this  condition  which  is  approximated 
in  disordered  states  in  man — in  fact,  when  from  any  cause  in- 
spiration is  very  labored  (asthma,  diphtheria,  etc.). 

In  man  and  most  mammals,  unlike  the  frog,  the  glottic 
opening  is  never  entirely  closed  during  any  part  of  the  respira- 
tory act,  though  it  undergoes  a  rhythmical  change  of  size, 
widening  during  inspiration  and  narrowing  during  expiration, 
in  accordance  with  the  action  of  the  muscles  attached  to  the 
arytenoid  cartilages,  the  action  of  which  may  be  studied  in 
man  by  means  of  the  laryngoscope. 

The  abdominal  muscles  have  a  powerful  rhythmical  action 
during  forced  respiration,  though  whether  they  function  dur- 
ing ordinary  quiet  breathing  is  undetermined ;  if  at  all,  prob- 
ably but  slightly.  Though  the  removal  of  the  external  inter- 
costals  in  the  dog  and  some  other  animals  reveals  the  fact  that 
the  internal  intercostals  contract  alternately  with  the  dia- 
phragm, it  must  not  be  regarded  as  absolutely  certain  that  such 
is  their  action  when  their  companion  muscles  are  present,  for 
Nature  has  more  ways  than  one  of  accomplishing  the  same  pur- 
pose— a  fact  that  seems  often  to  be  forgotten  in  reasoning  from 
experiments.     This  result,  however,  carries  some  weight  with  it. 

Types  of  Respiration. — There  are  among  mammals  two  princi- 
pal types  of  breathing  recognizable — the  costal  (thoracic)  and 
abdominal — according  as  the  movements  of  the  chest  or  the 
abdomen  are  the  more  pronounced. 

In  the  civilized  white  woman,  even  in  the  female  child,  the 
upper  thorax  takes  a  larger  share  in  respiration  than  in  the 
male  sex.  This  has  been  explained,  on  the  one  hand,  as  being 
due  to  artificial  influences,  modes  of  dress,  and  their  inherited 
effects ;  and  on  the  other  to  natural  ones,  the  crowding  of  the 
respiratory  organs,  owing  to  the  contents  of  the  pelvic  and 
abdominal  cavities  encroaching  on  the  thorax,  in  consequence 
of  the  enlargement  of  the  uterus  during  pregnancy.  It  has, 
however,  been  maintained  recently  that  an  examination  of 
pure-blooded  Indian  girls  does  not  show  the  features  of  respira- 
tion just  noticed  as  characteristic  of  the  breathing  of  white 
females,  the  inference  from  which  is  obvious.  But,  again,  it  is 
to  be  remembered  that  the  Indian  and  other  women  retaining 
primitive  habits  possess  a  power  of  adaptation  to  the  demands 
of  the  pregnant  condition  no  longer  shown  by  white  women. 
Thoracic  breathing  in  females  is  probably  the  result  of  several 
co-operating  causes,  of  which  usage  in  dress  is  one. 


374 


ANIMAL  PHYSIOLOGY. 


Personal  Observation. — The  student  would  do  well  at  this  stage 
to  test  the  statements  we  have  made  in  regard  to  the  respira- 
tory movements  on  the  human  subject  especially.  This  he 
can  very  well  do  in  his  own  person  when  stripped  to  the  waist 
before  a  mirror.  Many  of  the  abnormalities  of  the  forced  res- 
piration of  disease  may  be  imitated — in  fact,  this  is  one  of  the 
departments  of  physiology  in  which  the  human  aspects  may 
be  examined  into  by  a  species  of  experiment  on  one's  self  that 
is  as  simple  as  it  is  valuable. 


Pig.  305. — Protula  dysteri,  a  marine  annelid  living  in  a  calcareous  tube  constructed  by  itself 
(after  Huxley).  The  cut  represents  the  sexually  matiu-e  animal  (hermaphrodite)  extracted 
from  its  calcareous  tube,  a,  branchial  (.respiratory)  plumes,  abundantly  vascular ;  b, 
hood-like  expansion  of  anterior  end  of  body  ;  c,  mouth  ;  d,  stomach  ;  e,  anus  ;  /,  testes  ; 
g,  ova. 


THE  RESPIRATORY   SYSTEM. 


375 


Fig.  306. 


Fig.  306.— Vertical  transverse  section  of  fresh-water  mussel  (Anodon)  through  heart  (after 

Huxley).     l\  ventricle  ;  a.  auricles  ;  }•,  rectum  ;  p,  pericardium  ;  i,  inner,  o,  outer  gill ; 

o'.  vestibule  of  organ  of  Bojanus,  B  ;  /,  foot ;  ?n,  m,  mantle  lobes. 
Fig.  307.— Gill  of  fish  (perchi,  to  illustrate  relations  of  different  blood-vessels,  etc.,  concerned 

in  respiration  (after  Bell).    A,  branchial  artery  ;  B,  branchial  arch  seen  in  cross-section  ; 

V,  branchial  vein  ;  a,  v,  branches  of  artery  and  vein  respectively. 

Comparative. — It  is  hoped  that  the  various  figures  accompa- 
nied by  descriptions,  introduced  in  this  and  other  chapters,  will 
make  the  relations  of  the  circulation  and  respiration  in  the  va- 


Fia.  308.— Diagram  of  scorpion,  mf»st  of  the  appendages  having  been  removed  (after  Huxley). 
a,  mouth  ;  h,  alitnentary  tra«rt ;  c.  anus  ;  f/.  heart ;  f ,  pulmonary  sac  ;  /,  position  of  ven- 
tral ganglionaU'd  cord  ;  f/,  cerebral  ganglia;  T,  U-lson.  VII— XX,  seventh  to  twentieth 
Bomite.    IV,  V,  VI,  bawal  joints  of  pedipalpi  and  two  following  pairs  of  limbs. 


376 


ANIMAL  PHYSIOLOGY. 


rious  classes  of  animals^,  whether  terrestrial  or  aquatic,  evident 
without  extended  treatment  of  the  subject  in  the  text.     What 


~Pm 


Fig.  309. 

Fig.  309.— a.  Pulmonary  sac.    B.  respiratory  leaflets  of  Scorpio  occitanus  (after  Blanchard). 
Fig.  310.— Left  pulmonary  sac,  viewed  from  dorsal  aspect,  of  a  spider  (after  Duges).    pm, 
pulmonary  lamellae  ;  stg,  stigma,  or  opening  to  former. 

we  are  desirous  of  impressing  is  that  throughout  the  entire  ani- 
mal kingdom  resx3iration  is  essentially  the  same  process ;  that 


Fig.  311.-  -A.  B.  Tadpoles  with  external  branchice  (after  Huxley),  n,  nasal  sacs  ;  a,  eye ;  o, 
ear  ;  k.  b,  branchias  ;  m,  mouth  ;  z,  horny  jaws  ;  s,  suckers  ;  d,  opercular  (or  gill)  fold. 
C.  More  advanced  frog's  larva,  y,  rudiment  of  hind-limb  ;  fc.  s,  single  branchial  aperture. 
Owing  to  figure  not  having  been  reversed,  this  aperture  seems  to  lie  on  right  instead  of 
left  side. 

finally  it  resolves  itself  into  tissue-breathing :  the  appropria- 
tion of  oxygen  and  the  excretion  of  carbon  dioxide.  Since  the 
manner  in  which  oxygen  is  introduced  into  the  lungs  and  foul 
gases  expelled  from  them  in  some  reptiles  and  amphibians,  is 
largely  different  from  the  method  of  respiration  in  the  mam- 
mal, we  call  attention  to  this  process  in  an  animal  readily 
watched — the  common  frog.  This  creature,  by  depressing  the 
floor  of  the  mouth,  enlarges  his  air-space  in  this  region  and 
consequently  the  air  freely  enters  through  the  nostrils ;  where- 
upon the  latter  are  closed  by  a  sort  of  valve,  the  glottis  opened 


THE   RESPIRATORY   SYSTEM. 


377 


and  the  air  forced  into  tlie  lungs  by  the  elevation  of  the  floor 
of  the  mouth.  By  a  series  of  flank  movements  the  elasticity 
of  the  lungs  is  aided  in  expelling  the  air  through  the  now  open 
nostrils.  The  respiration  of  the  turtle  and  some  other  reptiles 
is  somewhat  similar.     In  the  case  of  aquatic  animals,  both  in- 


FiG.  312.— General  view  of  air-reservoirs  of  duck,  opened  inferiorly  :  also  their  relations  with 
principal  viscera  of  trunlc  (after  Happey).  1,  1,  anterior  extremity  of  cervical  reservoirs  ; 
2.  thoracic  reservoir  ;  3,  anterior  (liaphraginatic  reservoir  ;  4,  posterior  ditto  ;  5,  ahdorii- 
inal  reservoir:  a.  membrane  forming  anterior  diaphragmatic  reservoir;  6,  membrane 
forming  posterler  ditto  ;  (i,  section  of  tliorac()-iil)dominal  diapliragm  :  il.  suV)pect()ral  pro- 
longation of  thoracic  reservoir  ;  e,  j)ei-ic'ardiuiii ;  /,  /,  liver  ;  (j,  gizzard  ;  /i,  intestines  ;  in, 
heart ;  n,  n,  section  of  great  pectoral  miis(,-le  above  its  insertion  into  the  iunnerus  ;  o,  an- 
terior clavicle  ;  p,  posterior  clavicle  of  right  side  cut  and  turned  outward. 


vertebrate  and  vertebrate,  excepting  mammals,  the  blood  is 
freely  exposed  in  the  gills  to  oxygen  dissolved  in  the  water  as 
it  is  to  the  same  gas  mixed  with  nitrogen  in  terrestrial  animals. 
In  the  land-snail,  land-crab,  etc.,  we  have  a  sort  of  intermedi- 
ate condition,  the  gills  being  kept  moist.     It  is  not  to  be  for- 


378  ANIMAL   PHYSIOLOGY. 

gotten,  however,  that  normally  the  respiratory  tract  of  mam- 
mals is  never  other  than  slightly  moist. 

The  Quantity  of  Air  respired. 

We  distinguish  between  the  quantity  of  air  that  usually  is 
moved  by  the  thorax,  and  that  which  may  be  respired  under 
special  effort,  which,  of  course,  can  never  exceed  the  capacity 
of  the  respiratory  organs. 

Accordingly,  we  recognize:  1.  Tidal  air,  or  that  which 
passes  in  and  out  of  the  respiratory  passages  in  ordinary  quiet 
breathing,  amounting  to  about  500  cc,  or  thirty  cubic  inches. 
2.  CoTuplemental  air,  which  may  be  voluntarily  inhaled  by  a 
forced  inspiration  in  addition  to  the  tidal  air,  amounting  to 
1,500  cc,  or  about  100  cubic  inches.  3.  Supplemental  {reserve) 
air,  which  may  be  expelled  at  the  end  of  a  normal  respiration 
— i.  e.,  after  the  expulsion  of  the  tidal  air,  and  which  represents 
the  quantity  usually  left  in  the  lungs  after  a  normal  quiet 
expiration,  amounting  to  1,500  cc.  4.  Residual  air,  which  can 
not  be  voluntarily  expelled  at  all,  amounting  to  about  2,000  cc, 
or  120  cubic  inches. 

The  vital  capacity  is  estimated  by  the  quantity  of  air  that 
may  be  expired  after  the  most  forcible  inspiration.  This  will, 
of  course,  vary  with  the  age,  which  determines  largely  the  elas- 
ticity of  the  thorax,  together  with  sex,  position,  height,  and  a 
variety  of  other  circumstances.  But,  inasmuch  as  the  result 
may  be  greatly  modified  by  practice,  like  the  power  to  expand 
the  chest,  the  vital  capacity  is  not  so  valuable  an  indication  as 
might  at  first  be  supposed. 

It  is  important  to  bear  in  mind  that  the  tidal  air  is  scarcely 
more  than  sufficient  to  fill  the  upper  air-passages  and  larger 
bronchi,  so  that  it  requires  from  five  to  ten  respirations  to  re- 
move a  quantity  of  air  inspired  by  an  ordinary  act.  Very 
much  must,  therefore,  depend  on  diffusion,  the  quantity  of  air 
remaining  in  the  lungs  after  each  breath  being  the  sum  of  the 
residual  and  reserve  air,  or  about  3,500  cc.  (220  cubic  inches). 
Considering  the  creeping  slowness  of  the  capillary  circulation, 
it  would  not  be  supposed  that  the  respiratory  process  in  its 
essential  parts  should  be  the  rapid  one  that  a  greater  move- 
m.ent  of  the  air  would  imply. 


THE  RESPIRATORY  SYSTEM.  379 

The  Respiratory  Rhythm. 

In  man,  and  most  of  oiir  domestic  mammals,  a  definite  rela- 
tion between  the  cardiac  and  respiratory  movements  obtains, 
there  being  about  four  to  five  heart-beats  to  one  respiration, 
which  would  make  the  rate  of  breathing  in  man  about  sixteen 
to  eighteen  per  minute.  Usually,  of  course,  the  largest  animals 
have  the  slower  pulse  and  respiration ;  and  this  is  an  invariable 
rule  for  the  varieties  of  a  species,  as  observable  in  the  canine 
race,  to  mention  a  well-known  instance. 

The  rate  of  the  respiratory  movements  is  to  some  extent  a 
measure  of  the  rapidity  of  the  oxidative  processes  in  the  body, 
as  witness  the  slow  and  intermittent  breathing  of  cold-blooded 
animals  as  compared  with  the  more  rapid  respiration  of  birds 
and  mammals  (Fig.  313). 

Pathological. — Any  condition  that  lessens  the  amount  of  re- 
spiratory surface,  or  diminishes  the  mobility  of  the  chest-walls 
is  usually  accompanied  by  accelerated  movements,  but  beneath 
this  is  the  demand  for  oxygen,  part  of  the  avenues  by  which 
this  gas  usually  enters,  having  been  closed  or  obstructed  by  the 
disease.  So  that  it  is  not  surprising  that,  in  consequence  of 
the  effusion  of  fluid  into  the  thoracic  cavity,  leading  to  the 
compression  of  the  lung,  the  opposite  one  should  be  called  into 
more  frequent  use,  and  even  enlarge  to  meet  the  demand. 
These  facts  show  how  urgent  is  the  need  for  constant  ventila- 
tion of  the  blood,  and  at  the  same  time  how  great  is  the  power 
of  adaptation  to  meet  the  emergency. 

The  difference  between  the  inspiratory  and  the  expiratory 
rhythm  may  be  gathered  by  watching  the  movements  of  the 
bared  chest,  or  more  accurately  from  a  graphic  record.  It  is 
usually  considered  that  expiration  is  only  slightly  longer  than 
inspiration,  and  that  any  marked  deviation  from  this  relation 
should  arouse  suspicion  of  disease.  Normally  the  respiratory 
pause  is  very  slight,  so  that  insjjiration  seems  to  follow  di- 
rectly on  expiration ;  though  the  latter  act  reminds  us  of  the 
prolongation  of  the  ventricular  systole  after  the  blood  is  ex- 
f)ellod. 

If,  in  the  tracing,  the  small  waves  on  the  upper  part  of  the 
expiratory  curve  really  represent  the  effect  of  the  heart-beat,  it 
makes  it  easier  to  understand  how  such  might  assist  in  venti- 
lating the  bl(jod  when  the  respirations  occur  only  once  in  a 
considerable  interval  and  very  feebly  then,  as  in  hibernating 
animals  or  individuals  that  have  fainted ;  though  it  must  be 


380 


ANIMAL  PHYSIOLOGY. 


remembered  that  diffusion  is  a  ceaseless  process  in  all  liAdng 
vertebrates. 

It  is  scarcely  necessary  to  point  ont  tbat  the  respiratory 


Fig.  313, — Tracings  of  respiratory  movements  of  individuals  belonging  to  different  groups  of 
the  animal  kmgdom  (after  ThanhofEer).  Differences  in  depth,  frequency,  and  especially 
regularity,  are  very  noticeable.  1,  fish  ;  2,  tortoise ;  3,  adder  (in  winter) ;  4,  boa-con- 
strictor (in  summer) ;  5,  frog  ;  6,  alligator  ;  7,  lizard  ;  8,  canary-bird  ;  9,  adult  dog  ;  10, 
rabbit :  11,  man  ;  13,  dog ;  13,  horse.  Compare  these,  and  note  that  in  nl  respiration  is 
shallow,  and  in  ml  deep. 


movements  are  increased  by  exercise,  emotions,  position,  sea- 
son, hour  of  the  day,  taking  meals,  etc. 


THE   RESPIRATORY  SYSTEM. 


381 


Fig.  314.— Tracings  of  respiration  of  horse  when  at  rest  and  after  exercise  (after  Thanhoffer). 
/,  inspiration  ;  E,  expiration.  Spaces  between  vertical  lines  indicate  time  periods  of  one 
second  each.  1,  animal  standing  at  rest ;  3.  after  walk  of  few  minutes  ;  7  and  8,  after 
trotting  :  9,  after  a  brief  rest ;  li;  after  trotting  and  running  for  some  minutes  ;  17,  after 
resting  from  last  for  a  short  time  ;  51,  tracing  at  end  of  experiment. 

Eespiratory  Sounds. — The  entrance  and  exit  of  air  are  accom- 
panied by  certain  sounds,  which  vary  with  each  part  of  the 
respiratory  tract.  To  these  sounds  names  have  been  given,  but 
as  they  are  somewhat  inconstant  in  their  application,  or  at  least 
have  several  synonyms,  we  pass  them  by,  recommending  the 
student  to  actually  learn  the  nature  of  the  respiratory  murmurs 
by  listening  to  the  normal  chest  in  both  man  and  the  lower  ani- 
mals. With  the  use  of  a  double  stethoscope  he  may  practice  upon 
himself,  though  not  so  advantageously  as  in  the  case  of  the  heart. 

The  sf>unds  are  caused  in  part  by  the  friction  of  the  air, 
though  they  are  probably  complex,  several  factors  entering  into 
their  causation. 


Comparison  op  the  Inspired  and  Expired  Air. 

The  changes  that  take  i)lace  in  the  air  respired  may  be 
briefly  stated  as  follows : 


382  ANIMAL  PHYSIOLOGY. 

1.  Whatever  the  condition  of  the  inspired  air,  that  expired 
is  about  saturated  with  aqueous  vapor — i,  e.,  it  contains  all  that 
it  is  capable  of  holding  at  the  existing  temperature. 

2.  The  temperature  of  the  expired  air  is  about  that  of  the 
blood  itself,  so  that  if  the  air  is  very  cold  when  breathed,  the 
body  loses  a  great  deal  of  its  heat  in  warming  it.  The  expired 
air  of  the  nasal  passages  is  slightly  warmer  than  that  of  the 
mouth. 

3.  Experiment  shows  that  the  expired  air  is  really  dimin- 
ished in  volume  to  the  extent  of  from  one  fortieth  to  one  fiftieth 
of  the  whole.  Since  two  volumes  of  carbonic  anhydride  require 
for  their  composition  two  volumes  of  oxygen,  if  the  amount  of 
the  former  gas  expired  be  not  equal  to  the  amount  of  oxygen 
inspired,  some  of  the  latter  must  have  been  used  to  form  other 

CO 

combinations.     -~7^,  amounting  to  rather  less  than  1,  is  called 

the  respiratory  coefficient, 

4.  The  difference  between  inspired  and  expired  air  may  be 
gathered  from  the  following : 


Inspired  air. 
Expired  air . 


Oxygen. 

Nitrogen. 

Carbonic  dioxide. 

20-810 

79-150 

0-040 

16-033 

79-587 

4-380 

From  which  the  most  important  conclusions  to  be  drawn 
are,  that  the  expired  air  is  poorer  in  oxygen  to  the  extent  of 
4  to  5  per  cent,  and  richer  in  carbonic  anhydride  to  somewhat 
less  than  this  amount. 

From  experiment  it  has  been  ascertained  that  the  amount 
of  carbonic  dioxide  is  for  the  average  man  800  grammes  (406 
litres,  equivalent  to  !^18'1  grammes  carbon)  daily,  the  oxygen 
actually  used  for  the  same  period  being  700  grammes.  But 
the  variations  in  such  cases  are  very  great,  so  that  these  num- 
bers must  not  be  interpreted  too  rigidly.  Experience  proves 
that,  while  chemists  often  work  in  laboratories  in  which  the 
percentage  of  carbonic  anhydride  (from  chemical  decomposi- 
tions) reaches  5  per  cent,  an  ordinary  room  in  which  the  amount 
of  this  gas  reaches  1  per  cent  is  entirely  unfit  for  occupation. 
This  is  not  because  of  the  amount  of  the  carbon  dioxide  pres- 
ent, but  of  other  impurities  which  seem  to  be  excreted  in  pro- 
portion to  the  amount  of  this  gas,  so  that  the  latter  may  be 
taken  as  a  measure  of  these  poisons. 

What  these  are  is  as  yet  almost  entirely  unknown,  but  that 
they  are  poisons  is  beyond  doubt.     Small  effete  particles  of 


THE   RESPIRATORY  SYSTEM.  383 

once-living  protoplasm  are  carried  out  with  the  breath,  but 
these  other  substances  are  got  rid  of  from  the  blood  by  a  vital 
process  of  secretion  (excretion),  we  must  believe ;  which  shows 
that  the  lungs  to  some  degree  play  the  part  of  glands,  and  that 
their  whole  action  is  not  to  be  explained  as  if  they  were  merely 
moistened  bladders  acting  in  accordance  with  ordinary  physical 
laws. 

An  estimation  of  the  amount  of  atmospheric  air  required 
may  be  calculated  from  data  already  given. 

Thus,  assuming  that  a  man  gives  up  at  each  breath  4  per 
cent  of  carbon  dioxide  to  the  500  cc.  of  tidal  air  he  expires,  and 
breathes,  say,  seventeen  times  a  minute,  we  get  for  the  amount 
of  air  thus  charged  in  one  hour  to  the  extent  of  1  per  cent : 

500  X  4  X  i:  X60  =  2,040,000  cc,  or  2,040  litres. 

But  if  the  air  is  to  be  contaminated  to  the  extent  of  only 
^  per  cent  of  carbonic  anhydride,  the  amount  should  equal  at 
least  2,040  X  10  hourly. 

Respiration  in  the  Blood. 

It  may  be  noticed  that  arterial  blood  kept  in  a  confined 
space  grows  gradually  darker  in  color,  and  that  the  original 
bright  scarlet  hue  may  be  restored  by  shaking  it  up  with  air. 
When  the  blood  has  passed  through  the  capillaries  and  reached 
the  veins,  the  color  has  changed  to  a  sort  of  purple,  character- 
istic of  venous  blood.  Putting  these  two  facts  together,  we  are 
led  to  suspect  that  the  change  has  been  caused  in  some  way  by 
oxygen.  Exact  experiments  with  an  appropriate  form  of  blood- 
pump  show  that  from  one  hundred  volumes  of  blood,  whether 
arterial  or  venous,  about  sixty  volumes  of  gas  may  be  obtained ; 
that  this  gas  consists  chiefly  of  oxygen  and  carbonic  anhydride, 
but  that  the  proportions  of  each  jjresent  depends  upon  whether 
the  blood  is  arterial  or  venous. 

The  following  table  will  make  this  clear : 


Arterial  blood. 
Venous  blood.. 


Oxygen. 

Carbonic  anhydride. 

Nitrogen. 

20 

40 

1-3 

8-12 

46 

1-2 

from  100  volumes  of  blood  at  0°  C.  and  760  millimetre  pressure. 

Arterial  blood,  then,  contains  8  to  12  per  cent  more  oxygen 

and  about  C  par  cent  more  carbonic  dioxide  than  venous  blood. 

It  is  not,  of  course,  true,  as  is  sometimes  supposcid,  tliat  arterial 


384 


ANIMAL  PHYSIOLOGY. 


blood  is  "  pure  blood  "  in  the  sense  that  it  contains  no  carbonic 
anhydride,  as  in  reality  it  always  carries  a  large  percentage  of 
this  gas. 


Fig.  315.— Diagrammatic  illustration  of  Ludwig's  mercurial  gas-pump.  A  and  B  are  two 
glass  globes,  connected  by  strong  India-rubber  tubes,  with  two  similar  glass  globes, 
A'  and  B'.  A  is  further  connected  by  means  of  the  stop-cock  c  with  the  receiver  C, 
containing  the  blood  (or  other  fluid)  to  be  analyzed  ;  and  B,  by  means  of  the  stop-cock 
d  and  tube  e  with  the  receiver  Z),  for  receiving  the  gases.  A  and  B  are  also  connected 
with  each  other  by  means  of  the  stop-cocks  /  and  g,  the  latter  being  so  arranged  that  B 
also  communicates  with  B'  by  the  passage  g'.  A'  and  B'  being  full  of  mercury,  and  the 
cocks  fc,  /,  g  and  d  being  open,  but  c  and  g'  closed,  on  raising  A'  by  means  of  the  pulley  p 
the  mercury  of  A'  fills  A,  driving  out  the  air  contained  in  it  into  B,  and  so  out  through  e. 
When  the  mercury  has  risen  above  g,  f  is  closed  ;  and  g'  being  opened,  B'  is  in  turn  raised 
till  B  is  completely  filled  with  mercury,  all  the  air  previously  in  it  being  driven  out 
through  e.  Upon  closing  d  and  lowering  B',  the  whole  of  the  mercury  in  B  falls  into  B', 
and  a  vacuum  consequently  is  established  in  B.  On  closing  g'  but  opening  g,  /,  and  Ic.  and 
lowering  A',  a  vacuum  is  similarly  established  jn  A  and  in  the  junction  between  A  and  B. 
If  the  cock  c  be  now  opened,  the  gases  of  the  blood  in  C  escape  into  the  vacuum  of  A  and 
B.  By  raising  A'  after  the  closure  of  c  and  opening  of  d,  the  gases  so  set  free  are  driven 
from  A  into  B,  and  by  the  raising  of  B'  from  B  through  e  into  the  receiver  D,  standing 
over  mercury.     (After  Foster.) 

The  Conditions  under  which  the  Gases  exist  in  the  Blood. — If  a 

fluid,  as  water,  be  exposed  to  a  mixture  of  gases  which  it  can 


THE  RESPIRATORY   SYSTEM,  335 

absorb  under  pressure,  it  is  found  that  the  amount  taken  up 
depends  on  the  quantity  of  the  particuhir  gas  present  independ- 
ent of  the  presence  or  quantity  of  the  others ;  thus,  if  water 
be  exposed  to  a  mixture  of  oxygen  and  nitrogen,  the  quantity 
of  oxygen  absorbed  will  be  the  same  as  if  no  nitrogen  were 
present — i.  e,,  the  absorption  of  a  gas  varies  with  the  iJartial 
pressure  of  that  gas  in  the  atmosphere  to  which  it  is  exposed. 
But  whether  blood,  deprived  of  its  gases,  be  thus  exposed  to 
oxygen  under  pressure,  or  whether  the  attempt  be  made  to 
remove  this  gas  from  arterial  blood,  it  is  found  that  the  above- 
stated  law  does  not  apply. 

When  blood  is  f)laced  under  the  exhaustion-pump,  at  first 
very  little  oxygen  is  given  off ;  then,  when  the  pressure  is  con- 
siderably reduced,  the  gas  is  suddenly  liberated  in  large  quan- 
tity, and  after  this  comparatively  little.  A  precisely  analogous 
course  of  events  takes  place  when  blood  deprived  of  its  oxygen 
is  submitted  to  this  gas  under  pressure.  On  the  other  hand, 
if  these  experiments  be  made  with  serum,  absorption  follows 
according  to  the  law  of  pressures.  Evidently,  then,  if  the  oxy- 
gen is  merely  dissolved  in  the  blood,  such  solution  is  peculiar, 
and  we  shall  xjresently  see  that  this  supposition  is  neither  neces- 
sary nor  reasonable. 

HEMOGLOBIN   AND   ITS   DERIVATIVES. 

Haemoglobin  constitutes  about  y'V  of  the  corpuscles,  and, 
though  amorphous  in  the  living  blood-cells,  may  be  obtained 
in  crystals,  the  form  of  which  varies  with  the  animal ;  in- 
deed, in  many  animals  this  substance  crystallizes  spontane- 
ously on  the  death  of  the  red  cells.  It  is  unique  among  albu- 
minous compounds  in  being  the  only  one  found  in  the  animal 
body  that  is  susceptible  of  crystallization.  Its  estimated  com- 
position is : 

Carbon 53-85 

Hydrogen 7-33 

Nitrogen 1  G'17 

Oxygen 21-84 

Iron '43 

8ul{)liur -39 

together  witli  3  to  4  per  cent  of  water  of  crystallization. 

The  formula  assigned  is:  CgooHasoOnsNiMFeSg.  The  molecular 
constitution  is  not  known,  and  the  above  formula  is  merely  an 
approximation,  wliich  will,  however,  servo  to  convey  an  idea 

2.-5 


386 


ANIMAL  PHYSIOLOGY. 


of  the  great  complexity  of  this  compound.     The  presence  of 
iron  seems  to  be  of  great  importance.     If  not  the  essential 

respiratory  constituent,  cer- 
tainly the  administration  of 
this  metal  in  some  form 
proves  very  valuable  when 
the  blood  is  deficient  in 
hsemoglobin. 

This  substance  can  be 
recognized  most  certainly  by 
the  spectroscope.  The  ap- 
pearances vary  with  the 
strength  of  the  solution, 
and,  as  this  test  for  blood 
(haemoglobin)  is  of  much 
practical  importance,  it  will 
be  necessary  to  dwell  a  little 
upon  the  subject ;  though, 
after  a  student  has  once  rec- 
ognized clearly  the  differ- 
ences of  the  spectrum  ap- 
pearances, he  has  a  sort  of 
knowledge  that  no  verbal 
description  can  convey.  This 
is  easily  acquired.  One  only 
needs  a  small,  flat-sided  bot- 
tle and  a  pocket  -  spectro- 
scope. Filling  the  bottle 
half -full  of  water,  and  getting  the  spectroscope  so  focused  that 
the  Fraunhofer  lines  appear  distinctly,  blood,  blood-stained 
serum,  a  solution  of  hsemoglobin-crystals,  or  the  essential  sub- 
stance in  any  form  of  dilute  solution,  may  be  added  drop  by 
drop  till  changes  in  the  spectrum  in  the  form  of  dark  bands 
appear.  By  gradually  increasing  the  quantity,  appearances 
like  those  figured  below  may  be  observed,  though,  of  course, 
much  will  depend  on  the  thickness  of  the  layer  of  fluid  as  to 
the  quantity  to  be  added  before  a  particular  band  comes  into 
view. 

When  wishing  to  be  precise,  we  speak  of  the  most  highly 
oxidized  form  of  haemoglobin  as  oxy-hgemoglobin  (0-H),  and 
the  reduced  form  as  haemoglobin  simply,  or  reduced  hsemo- 
globin  (H). 

By  a  comparison  of  the  spectra  it  will  be  seen  that  the  bands 


Fig.  316.  —  Crystallized  haemoglobin  (Gautier). 
a.  b,  crystals  f i  cm  venous  blood  of  man  ;  c, 
from  blood  of  cat ;  d,  of  Guinea-pig ;  e,  of 
marmot ;  /,  of  squirrel. 


THE  RESPIRATORY   SYSTEM. 


387 


of  oxy-h£emoglobin  lie  between  the  D  and  E  lines;  that  the 
left  band  near  D  is  always  the  most  definite  in  outline  and  the 


-=  §  £  S  te 


most  pronounced  in  every  respect  except  breadth;  that  it  is  in 
weak  solutions  the  first  to  appear,  and  tlie  last  to  disappear  on 


388  ANIMAL  PHYSIOLOGY. 

reduction ;  that  there  are  two  instances  in  which,  there  may  be 
a  single  band  from  haemoglobin — in  the  one  case  when  the  solu- 
tion is  very  dilute  and  when  it  is  very  concentrated.  These 
need  never  be  mistaken  for  each  other  nor  for  the  band  of  re- 
duced hsemoglobin.  The  latter  is  a  hazy  broad  band  with  com- 
paratively indistinct  outlines,  and  darkest  in  the  middle. 

It  will  be  further  noticed  that  in  all  these  instances,  apart 
from  the  bands,  the  spectrum  is  otherwise  modified  at  each 
end,  so  that  the  darker  the  more  centrally  placed  characteristic 
bands,  the  more  is  the  light  at  the  same  time  cut  oft*  at  each 
end  of  the  spectrum. 

If,  now,  to  a  specimen  showing  the  two  bands  of  oxy-hsemo- 
globin  distinctly  a  few  drops  of  ammonium  sulphide  or  other 
reducing  agent  be  added,  a  change  in  the  color  of  the  solution 
will  result,  and  the  single  hazy  band  characteristic  of  hsemo- 
globin will  appear. 

It  is  not  to  be  supposed,  however,  that  venous  blood  gives 
this  spectrum.  Even  after  asphyxia  it  will  be  difficult  to  see 
this  band,  for  usually  some  of  the-  oxy-haemoglobin  remains 
reduced ;  but  it  is  worthy  of  note,  as  showing  that  the  appear- 
ances are  normal,  that  the  blood,  viewed  through  thin  tissues 
when  actually  circulating,  whether  arterial  or  venous,  gives 
the  spectrum  of  oxy-hsemoglobin.  At  the  same  time  there  can 
be  no  doubt  that  the  changes  in  color  which  the  blood  under- 
goes in  passing  through  the  capillaries  is  due  chiefly  to  loss  of 
oxygen,  as  evidenced  by  the  experiments  before  referred  to ;  and 
the  reason  that  the  two  bands  are  always  to  be  seen  in  venous 
blood  is  simply  that  enough  oxy-haemoglobin  remains  to  give 
the  two-band  spectrum  which  prevails  over  that  of  (reduced) 
hsemoglobin.  We  are  thus  led  by  many  paths  to  the  important 
conclusion  that  the  red  corpuscles  are  oxygen-carriers,  and, 
though  this  may  not  be  and  probably  is  not  their  only  func- 
tion, it  is  without  doubt  their  principal  one.  Of  their  oxygen 
they  are  being  constantly  relieved  by  the  tissues ;  hence  the 
necessity  of  a  circulation  of  the  blood  from  a  respiratory  point 
of  view. 

There  are  other  gases  that  can  replace  oxygen  and  form 
compounds  with  hsemoglobin ;  hence  we  have  CO-hsemoglobin 
and  NO-hsemoglobin,  which  in  turn  are  replaced  by  oxygen  with 
no  little  difficulty — a  fact  which  explains  why  carbonic  oxide  is 
so  fatal  when  respired,  and,  as  it  is  a  constituent  of  illuminat- 
ing gas,  the  cause  of  the  death  of  those  inhaling  the  latter  is 
often  not  far  to  seek.     Blood  may,  in  fact,  be  saturated  with 


THE  RESPIRATORY   SYSTEM.  389 

carbonic  oxide  by  allowing  illuminating  gas  to  pass  through  it, 
when  a  change  of  color  to  a  cherry  red  may  be  observed,  and 
which  will  remain  in  spite  of  prolonged  shaking  up  with  air  or 
attempts  at  reduction  with  the  usual  reagents.  Haemoglobin 
may  be  resolved  into  a  proteid  (globin)  not  well  understood, 
and  hcemaiiii.  This  happens  when  the  blood  is  boiled  (perhaps 
also  in  certain  cases  of  lightning-stroke),  and  when  strong  acids 
are  added.  Hsematin  is  soluble  in  dilute  acids  and  alkalies,  and 
has  then  characteristic  spectra.  Alkaline  hsematin  may  be  re- 
duced ;  and,  as  the  iron  can  be  separated,  resulting  in  a  change 
of  color  to  brownish  red,  after  which  there  are  no  longer  any 
reducing  effects,  it  would  seem  that  the  oxygen-carrying  power 
and  iron  are  associated.  This  iron-free  hsematin  is  named 
hceniatopnrphyrin  or  luemaioin.. 

Hmmin  is  hydrochlorate  of  hsematin  (Teichmann's  crystals), 
and  may  be  formed  by  adding  glacial  acetic  acid  and  common 
salt  to  blood,  dried  blood-clot,  etc.,  and  heating  to  boiling.  This 
is  one  of  the  best  tests  for  blood,  valuable  in  medico-legal  and 
other  cases. 

When  oxy-hsemoglobin  stands  exposed  to  the  air,  or  when 
diffused  in  urine,  it  changes  color  and  becomes,  in  fact,  another 
substance — methcemoglohin,  irreducible  by  other  gases  (CO,  etc.), 
and  not  surrendering  its  oxygen  in  vacuo,  though  giving  it  up 
to  ammonium  sulphide,  becoming  again  oxy-hsemoglobin,  when 
shaken  up  with  atmospheric  air.  Its  spectrum  differs  from 
that  of  oxy-hsemoglobin  in  that  it  has  a  band  in  the  red  end  of 
the  spectrum  between  the  C  and  D  lines.  Hcematoidin  is  some- 
times found  in  the  body  as  a  remnant  of  old  blood-clots.  It  is 
probably  closely  allied  to  if  not  identical  with  the  hiliruhin 
of  bile. 

Comparative. — While  haemoglobin  is  the  respiratory  agent  in 
all  the  groups  of  vertebrates,  this  is  not  true  of  the  inverte- 
brates. Red  blood-cells  have  as  yet  been  found  in  but  a  few 
species,  though  haemoglobin  does  exist  in  the  blood  plasma  of 
several  groups,  to  one  of  which  the  earth-worm  and  several 
other  anneli<ls  belong.  It  is  interesting  to  note  that  the  respir- 
atory compound  in  certain  families  of  crustaceans,  as  the  com- 
mon crab,  horseshoe-crab  (limulus),  etc.,  is  blue,  and  that  in 
this  substance  cojiper  seems  to  take  thf;  place  of  iron. 

The  Nitrogen  and  the  Carbon  Dioxidfe  of  the  Blood. — The  little 
nitrogf'ii  whicli  is  found  iu  alxnit  equal  (piaiitity  in  venous  and 
arterial  blood,  seems  to  be  simply  dissolved.  The  relations  of 
carbonic  anhydride  are  much  more  complex  and  ob.scure.     The 


390  ANIMAL   PHYSIOLOGY. 

main  facts  known  are  that — 1.  The  quantity  of  this  gas  is  as 
great  in  serum  as  in  blood,  or,  at  all  events,  the  quantity  in 
serum  is  very  large.  2.  The  greater  part  may  be  extracted  by 
an  exhaustion-pump ;  but  a  small  percentage  (3  to  5  volumes 
per  cent)  does  not  yield  to  this  method,  but  is  given  off  when 
an  acid  is  added  to  the  serum.  3.  If  the  entire  blood  be  sub- 
jected to  a  vacuum,  the  whole  of  the  COa  is  given  off. 

From  these  facts  it  has  been  concluded  that  the  greater  part 
of  the  CO2  exists  in  the  plasma,  associated  probably  with  sodium 
salts,  as  sodium  bicarbonate,  but  that  the  corpuscles  in  some 
way  determine  its  relations  of  association  and  disassociation. 
Some  think  a  good  deal  of  this  gas  is  actually  united  with  the 
red  corpuscles. 

We  may  now  inquire  into  the  more  intimate  nature  of  respi- 
ration in  the  blood.  From  the  facts  we  have  stated  it  is  obvi- 
ous that  respiration  can  not  be  wholly  explained  by  the  Henry- 
Dalton  law  of  pressures  or  any  other  physical  law.  It  is  also 
plain  that  any  explanation  which  leaves  out  the  principle  of 
pressure  must  be  incomplete. 

While  there  is  in  oxy-hsemoglobin  a  certain  quantity  of  oxy- 
gen, which  is  intra-molecular  and  incapable  of  removal  by  re- 
duction of  pressure,  there  is  also  a  portion  which  is  subject  to 
this  law,  though  in  a  peculiar  way;  nor  is  the  question  of 
temperature  to  be  excluded,  for  experiment  shows  that  less 
oxygen  is  taken  up  by  blood  at  a  high  than  at  a  low  tempera- 
ture. 

We  have  learned  that,  in  ordinary  respiration,  the  propor- 
tion of  carbonic  dioxide  and  oxygen  in  different  parts  of  the 
respiratory  tract  must  vary  greatly ;  the  air  of  necessity  being 
much  less  pure  in  the  alveoli  than  in  the  larger  bronchi. 

From  experiments  on  blood,  venous  and  arterial,  to  deter- 
mine the  conditions  of  pressure,  temperature,  etc.,  under  which 
the  injurious  gas  is  got  rid  of  and  the  necessary  one  absorbed, 
it  has  been  found  that  the  partial  pressure  of  oxygen  in  the 
lungs  is  sufficient  to  bring  about  that  surrender  of  oxygen  to 
the  blood  necessary  to  keep  it  all  but  saturated  with  this  gas 
as  it  is  believed  to  be ;  and  that,  so  far  as  carbonic  anhydride 
is  concerned,  the  same  law  holds — i.  e.,  the  partial  pressure  in 
the  blood  is  ordinarily  greater  than  in  the  alveoli. 

By  means  of  an  apparatus  by  which  one  of  the  smaller 
bronchi  may  be  occluded  for  a  certain  period,  and  also  allow 
of  withdrawal  of  samples  of  the  air  in  the  occluded  portion  of 
lung  from  time  to  time,  to  ascertain  its  composition,  attempts 


THE  RESPIRATORY  SYSTEM.  391 

have  been  made  to  determine  the  joressure  relations  within  an 
alveolus.  It  is  maintained  that  while  the  partial  pressure  of 
the  carbonic  anhydride  rises  and  of  the  oxygen  sinks,  still  that 
they  remain  such  as  to  favor  respiration.  It  is  also  found  that, 
in  the  asphyxia  following  occlusion  of  the  trachea,  the  tension 
of  oxygen  is  always  greater,  and  of  carbonic  anhydride  less,  in 
the  alveoli  than  in  the  blood.  On  the  other  hand  it  is  stated 
that  oxy-hsemoglobin  is  found  in  the  blood  when  every  trace  of 
oxygen  is  removed  from  a  chamber  in  which  an  asphyxiating 
animal  is  breathing,  so  that  it  is  argued  that  partial  pressures 
alone  can  not  explain  the  facts  of  respiration,  and  that  this 
function  is  fundamentally  a  chemical  process ;  and  it  is  cus- 
tomary to  speak  of  the  oxygen  of  oxy-hsemoglobin  as  being  in 
a  state  of  "  loose  chemical  combination." 

The  entire  truth  seems  to  lie  in  neither  view,  though  both 
are  partially  correct. 

The  view  expressed  by  some  physiologists,  to  the  effect  that 
diffusion  explains  the  whole  matter,  so  far,  at  least,  as  carbonic 
anhydride  is  concerned,  and  that  the  epithelial  cells  of  the  lung 
have  no  share  in  the  respiratory  process,  does  not  seem  to  be 
in  harmony  either  with  the  facts  of  respiration  or  with  the 
laws  of  biology  in  general.  Why  not  say  at  once  that  the  facts 
of  respiration  show  that,  here  as  in  other  parts  of  the  economy, 
while  physical  and  chemical  laws,  as  we  know  them,  stand 
related  to  the  vital  processes,  yet,  by  reason  of  being  vital 
processes,  we  can  not  explain  them  according  to  the  theories  of 
either  physics  or  chemistry  ?  Surely  this  very  subject  shows 
that  neither  chemistry  nor  physics  is  at  present  adequate  to 
explain  such  processes.  It  is,  of  course,  of  value  to  know  the 
circumstances  of  tension,  temperature,  etc.,  under  which  respi- 
ration takes  place.  We,  however,  maintain  that  these  are  con- 
ditions only — essential  no  doubt,  but,  though  important,  that 
they  do  not  make  up  the  process  of  respiration.  But,  because 
we  do  not  know  the  real  explanation,  let  us  not  exalt  a  few 
facts  or  theories  of  chemistry  or  physics  into  a  solution  of  a 
complex  x^roblem.  Besides,  some  of  the  experiments  on  which 
the  conclusions  have  been  based  are  questionable,  inasmuch  as 
they  seem  to  induce  artificial  conditions  in  the  animals  oper- 
ated upon ;  and  we  have  already  insisted  on  the  blood  being 
regarded  as  a  living  tissue,  behaving  differently  in  the  body 
and  when  isohited  from  it,  so  that  even  in  so-called  blood-gas 
experiments  tliere  may  be  sources  of  fallacy  inherent  in  the 
nature  of  the  case. 


392  ANIMAL   PHYSIOLOGY. 

Foreign  Gases  and  Respiration. — These  are  divided  into : 

1.  Indifferent  gases,  as  N,  H,  CH4,  which.,  though  not  in 
themselves  injurious,  are  entirely  useless  to  the  economy. 

2.  Poisonous  gases,  fatal,  no  matter  how  abundant  the  nor- 
mal respiratory  food  may  be.  They  are  divisible  into :  (a)  those 
that  kill  by  displacing  oxygen,  as  NO,  CO,  HCN;  (&)  narcotic 
gases,  as  CO2,  ISTjO,  producing  asphyxia  when  present  in  large 
quantities ;  (c)  reducing  gases,  as  H2S,  (^114)28,  PH3,  AsHs,  C2N2, 
which  rob  the  haemoglobin  of  its  oxygen. 

There  are  probably  a  number  of  poisonous  products,  some 
of  them  possibly  gases,  produced  by  the  tissues  themselves  and 
eliminated  normally  by  the  respiratory  tract ;  and  these  are 
doubtless  greatly  augmented,  either  in  number  or  quantity,  or 
both,  when  other  excreting  organs  are  disordered. 

Eespiration  in  the  Tissues. 

"We  first  direct  attention  to  certain  striking  facts  : 
1.  An  isolated  (frog's)  muscle  will  continue  to  contract  for 
a  considerable  period  and  to  exhale  carbon  dioxide  in  the  total 
absence  of  oxygen,  as  in  an  atmosphere  of  hydrogen ;  though, 
of  course,  there  is  a  limit  to  this,  and  a  muscle  to  which  either 
no  blood  flows,  or  only  venous  blood,  soon  shows  signs  of 
fatigue.  2.  In  a  frog,  in  which  physiological  saline  solution 
has  been  substituted  for  blood,  the  metabolism  will  continue, 
carbonic  anhydride  being  exhaled  as  usual.  3.  Substances, 
which  are  readily  oxidized,  when  introduced  into  the  blood  of 
a  living  animal  or  into  that  blood  when  withdrawn  undergo 
but  little  oxidative  change.  4.  An  entire  frog  will  respire  car- 
bonic dioxide  for  hours  in  an  atmosphere  of  nitrogen. 

Such  facts  as  these  seem  to  teach  certain  lessons  clearly.  It 
is  evident,  first  of  all,  that  the  oxidative  processes  that  give  rise 
to  carbon  dioxide  occur  chiefly  in  the  tissues  and  not  in  the 
blood ;  that  in  the  case  of  muscle  the  oxygen  that  is  used  is  first 
laid  by,  banked  as  it  were  against  a  time  of  need,  in  the  form  of 
intra-molecular  oxygen,  which  is  again  set  free  in  the  form  of 
carbon  dioxide,  but  by  what  series  of  changes  we  are  quite  un- 
able to  say.  Though  our  knowledge  of  the  respiratory  processes 
of  muscle  is  greater  than  for  any  other  tissue,  there  seems  to 
be  no  reason  to  believe  that  they  are  essentially  different  else- 
where. The  advantages  of  this  banking  of  oxygen  are,  of  course, 
obvious ;  were  it  otherwise,  the  life  of  every  cell  must  be  at  the 
mercy  of  the  slightest  interruption  of  the  flow  of  blood,  the 


THE  RESPIRATORY   SYSTEM.  393 

entrance  of  air,  etc.  Even  as  it  is,  the  need  of  a  constant  supply 
of  oxygen  in  warm-blooded  animals  is  much  greater  than  in 
cold-blooded  creatures,  which  can  long  endure  almost  entire 
cessation  of  both  respiration  and  circulation,  owing  to  the  com- 
paratively slow  rate  of  speed  of  the  vital  machinery. 

If  one  were  to  rely  on  mere  appearances  he  might  suppose 
that  in  the  more  active  condition  of  certain  organs  there  was 
less  chemical  interchange  (respiration)  between  the  blood  and 
the  tissues  than  in  the  resting  stage,  or,  properly  speaking, 
more  tranquil  stage,  for  it  must  be  borne  in  mind  that  a  living 
cell  is  never  wholly  at  rest ;  its  molecular  changes  are  cease- 
less. It  happens,  e.  g.,  that  when  certain  glands  (salivary)  are 
secreting  actively,  the  blood  flowing  from  them  is  less  venous 
in  appearance  than  when  not  functionally  active.  This  is  not 
because  less  oxygen  is  used  or  less  abstracted  from  the  blood, 
but  because  of  the  greatly  increased  speed  of  the  blood-flow,  so 
that  the  total  supply  to  draw  from  is  so  much  larger  that, 
though  more  oxygen  is  actually  used,  it  is  not  so  much  missed, 
nor  do  the  greater  additions  of  carbon  dioxide  so  rapidly  pol- 
lute this  rapid  stream. 

It  is  thus  seen  that  throughout  the  animal  kingdom  respira- 
tion is  fundamentally  the  same  process.  It  is  in  every  case 
finally  a  consumption  of  oxygen  and  production  of  carbonic 
anhydride  by  the  individual  cell,  whether  that  be  an  Amoeba 
or  an  element  of  man's  brain.  These  are,  however,  but  the 
beginning  and  end  of  a  very  complicated  biological  history  of 
by  far  the  greater  part  of  which  nothing  is  yet  known ;  and  it 
must  be  admitted  that  diffusion  or  any  physical  explanation 
carries  us  but  a  little  way  on  toward  the  understanding  of  it. 

The  Nervous  System  in  Relation  to  Respiration. 

We  have  considered  the  muscular  movements  by  which  the 
air  is  made  to  enter  and  leave  the  lungs  in  consequence  of 
changes  in  the  diameters  of  the  air-inclosing  case,  the  thorax. 
It  remains  to  examine  into  the  means  by  which  these  muscles 
were  set  into  harmonious  action  so  as  to  accomplish  the  pur- 
pose. The  nerves  supplying  the  muscles  of  respiration  are  de- 
rived from  the  spinal  cord,  so  that  they  must  be  under  the 
dominion  of  central  nerve-cells  situated  either  in  the  cord  or 
the  brain.  Is  the  influence  that  proceeds  outward  generated 
within  the  cells  independently  of  any  afferent  impulses,  or  is  it 
dependent  on  such  causes  ?    Let  us  appeal  to  facts. 


394  ANIMAL   PHYSIOLOGY. 

1.  If  the  phrenics,  an  intercostal  nerve,  etc.,  be  cut,  there  is 
a  corresponding  paralysis  of  the  muscle  supplied.  2.  If  the 
spinal  cord  be  divided  below  the  medulla  oblongata,  there  is  a 
cessation  of  all  respiratory  movements  except  those  of  the 
larynx  and  face,  which  also  disappear  if  the  facial  and  recur- 
rent laryngeal  nerves  be  divided.  3.  So  long  as  the  medulla 
remains,  respiration  may  continue ;  but  if  even  a  small  part  of 
this  region,  situated  below  the  vaso-motor  center  between  this 
and  the  calamus  scriptorius  (respiratory  center,  no&ud  vital), 
be  injured,  death  ensues  rapidly.  Plainly,  then,  there  are  cen- 
tral cells  which  originate  the  impulses  that  energize  the  mus- 
cles. 

It  remains  to  inquire  still  whether  they  are  independent 
(automatic)  centers,  or  are  influenced  by  impulses  reaching 
them  from  without.  Is  the  government  absolute,  or  subject  to 
the  will  of  the  multitudinous  cells  of  the  organic  common- 
wealth ? 

Again  let  us  appeal  to  facts:  1.  If  one  vagus  nerve  be  cut, 
a  change  is  observable  in  the  respiratory  rhythm,  which  is 
much  more  pronounced  if  both  nerves  be  divided.  Respiration 
becomes  slower,  and  the  pause  between  inspiration  and  expira- 
tion greatly  lengthened,  though  the  gaseous  interchange  re- 
mains much  as  before.  2.  If  one  suddenly  step  into  a  cold 
bath,  he  naturally  draws  a  long  breath.  Again,  the  respiration 
is  very  greatly  altered  in  consequence  of  emotional  changes ; 
indeed,  there  is  probably  no  rhythm  in  the  body  more  subject 
to  frequent  obvious  alteration  than  that  of  respiration.  3. 
Stimulation  of  the  central  end  of  such  a  nerve  as  the  sciatic 
causes  marked  change  in  the  rhythm  of  breathing.  4.  Stimu- 
lation of  the  central  end  of  the  vagus  usually  quickens  res- 
piration, while  stimulation  of  the  central  end  of  the  superior 
laryngeal  has  the  opposite  effect.  If  the  current  be  strong, 
respiration  may  be  arrested  in  each  instance,  though  in  a  differ- 
ent manner.  In  the  case  of  vagus  stimulation  the  result  is 
inspiratory  spasm,  and  of  the  superior  laryngeal  expiratory 
spasm. 

These  and  a  host  of  additional  facts,  experimental  and  other, 
show  that  the  central  impulses  are  modified  by  afferent  im- 
pulses reaching  the  center  through  appropriate  nerves.  More- 
over, drugs  seem  to  act  directly  on  the  center  through  the 
blood. 

The  vagus  is  without  doubt  the  afferent  respiratory  nerve, 
though  how  it  is  affected,  whether  by  the  mechanical  movement 


THE   RESPIRATORY   SYSTEM. 


395 


of  the  lungs  merely,  by  the  condition  of  the  blood  as  regards  its 
contained  gases,  or,  as  seems  most  likely,  by  a  combination  of 
circumstances   into  which  these  enter  and  are  probablj^  the 


Brain  above  medulla  from  which 
impulses  modifying  respiration 
may  proceed. 


'acial  miiscles. 


Respiratory  centre 
in  the  meduna. 


Cutaneous  surf  ace  from  which 
afferent  impulses  proceed  di- 
rectly  to  brain. 


Thoracic  resp.  muscles. 


Sptnal  cord 


.(— Respiratory  tract. 


Biaphragm  with 
phrenic  nerve. 


Cutaneous  sur- 
face from  which 
imjmhea  reach  res- 
piratory centre  by 
spinal  cord. 


Fio.  81ft.— Diap^m  Intended  to  illustrate  nervous  mechanism  of  respiration.    Arrows  indicate 

course  of  iuipulses. 


principal,  is  not  demonstrably  clear.     When  others  function  as 
afferent  nerves,  capable  of  modifying  the  action  of  tlie  respira- 


396  ANIMAL   PHYSIOLOGY. 

tory  center,  they  are  probably  influenced  by  the  respiratory 
condition  of  tlie  bloody  though  not  necessarily  exclusively. 

But  when  all  the  principal  afferent  impulses  are  cut  off  by 
division  of  the  nerves  reaching  the  respiratory  center  directly 
or  indirectly,  respiration  will  still  continue,  provided  the  motor 
nerves  and  the  medulla  remain  intact. 

The  center,  then,  is  not,  mainly  at  least,  a  reflex  but  an  auto- 
matic one,  though  its  action  is  modified  by  afferent  impulses 
reaching  it  from  every  quarter.  Since  respiration  continues 
when  the  medulla  is  divided  in  the  middle  line,  yet  is  modified 
unilaterally  when  one  vagus  is  divided,  it  is  inferred  that  the 
respiratory  center  is  double,  that  each  half  usually  works  in' 
harmony  with  the  other,  but  that  each  can  act  independently. 
Though  it  seems  clear  enough  that  the  respiratory  center  is 
automatic,  and  that  its  action  is  modified  according  to  the  con- 
dition of  the  organism  generally,  as  communicated  to  it  by  the 
various  afferent  nerves  and  the  blood  itself,  yet  the  exact  man- 
ner of  its  action — why  inspiration  follows  up  expiration — has 
not  been  clearly  explained.  Some  assume  that  during  expira- 
tion inspiratory  impulses  are  gathering  head  and  finally  check 
expiration  by  originating  inspiration,  while  these  are  opposed 
by  another  process  which  at  length  gives  rise  to  enough  resist- 
ance to  check  inspiration,  and  originate  expiration;  and  this 
theory  becomes  more  complete  if  an  expiratory  as  well  as  in- 
spiratory center  be  assumed. 

We  have  hitherto  spoken  only  of  a.  single  respiratory  cen- 
ter in  the  medulla,  but  certain  experimental  facts  throw  addi- 
tional light  on  the  subject. 

In  young  mammals — e.  g.,  kittens — it  is  found  that,  in  the 
absence  of  the  medulla,  respiratory  movements  may  be  induced 
by  stimulating  (pinching)  the  surface,  especially  if  the  action 
of  the  spinal  cord  be  augmented  by  the  administration  of 
strychnia.  From  this  it  has  been  inferred  that  there  are  respir- 
atory centers  in  the  spinal  cord,  subordinate  to  the  main  cen- 
ter in  the  medulla.  Considering  the  imperfect  nature  of  the 
respiratory  act  as  thus  induced,  and  the  circumstances  of  the 
case,  the  conclusion  has  the  appearance  of  being  a  little  strained. 
But  quite  recently  it  has  been  shown  that  in  the  adult  dog 
when  the  cord  is  severed  below  the  medulla,  and  artificial  res- 
piration maintained  for  some  time,  on  ceasing  this,  breathing 
begins  spontaneously  and  continues  for  a  considerable  period ; 
and  the  expiratory  phase  of  respiration  in  this  case  is  the  most 
marked.     It  has  been  argued  from  this  experiment  that  there 


THE  RESPIRATORY   SYSTEM.  397 

are  both  inspiratory  and  expiratory  centers  in  the  spinal  cord. 
But,  as  We  have  pointed  out,  on  more  than  one  occasion,  we 
must  always  be  on  our  guard  in  interpreting  the  behavior  of 
one  part  when  another  is  out  of  gear.  There  is  so  much  latent 
resource,  so  great  a  power  to  resume  functions  normally  laid 
aside,  if  not  wholly  in  great  part,  that  we  should  hesitate  be- 
fore inferring  that  the  spinal  cord  usually  takes  a  prominent 
share  in  originating  the  impulses  which  govern  respiration. 
Notwithstanding  the  suggestiveness  of  such  experiments,  we 
do  not  think  they  make  the  medulla  appear  in  a  less  important 
light  as  the  part  of  the  nervous  system  dominant  in  respira- 
tion ;  though  there  may  be  nervous  machinery  in  the  cord  usu- 
ally in  feeble  action,  susceptible  of  assuming  a  more  exalted 
functional  role  when  occasion  urgently  demands  and  when  en- 
couraged, so  to  speak,  to  do  so,  as  in  the  experiments  referred 
to  above ;  indeed  such,  upon  our  own  theory  of  physiological 
reversion,  would  naturally  be  the  case.  We  must,  however, 
draw  the  line  between  what  is  and  what  may  be  in  function. 

The  Influence  of  the  Condition  of  the  Blood  in  Respiration. — If 
for  any  reason  the  tissues  are  not  receiving  a  due  supply  of 
oxygen,  they  manifest  their  disapproval,  to  speak  figuratively, 
by  reports  to  the  responsible  center  in  the  medulla,  and  if  the 
medulla  is  a  sharer  in  the  lack,  as  it  naturally  would  be,  it  takes 
action  independently.  One  of  the  most  obvious  instances  in 
which  there  is  oxygen  starvation  is  when  there  is  hindrance  to 
the  entrance  of  air,  owing  to  obstruction  in  the  respiratory^ 
tract. 

At  first  the  breathing  is  merely  accelerated,  with  perhaps 
some  increase  in  the  depth  of  the  inspirations  (hyjierpnoRCi),  a 
stage  which  is  soon  succeeded  by  labored  breathing  {dyspncea), 
which,  after  the  medulla  has  called  all  the  muscles  usually  em- 
jjloyed  in  respiration  into  violent  action,  passes  into  convul- 
sions, in  wliich  every  muscle  may  take  part. 

In  other  words,  the  respiratory  impulses  not  only  pass  along 
their  usual  paths  as  energetically  as  possible,  but  radiate  into 
unusual  ones  and  pass  by  nerves  not  commonly  thus  set  into 
functional  activity. 

It  would  be  more  correct,  perhaps  to  assume  that  the  vari- 
ous parts  of  the  nervous  system  are  so  linked  together  that  ex- 
cessive activity  of  one  set  f)f  connections  acts  like  a  stimulus  to 
rouse  another  .set  into  action,  the  order  in  which  this  happens 
depending  on  the  law  of  habit — habit  personal  and  especially 
ancestral.     An  opposite  condition  to  that  described,  known  as 


398  ANIMAL  PHYSIOLOGY. 

apncBa,  may  be  induced  by  pumping  air  into  an  animal's  chest 
very  rapidly  by  a  bellows ;  or  in  one's  self  by  a  succession  of 
rapid,  deep  respirations. 

After  ceasing,  the  breathing  may  be  entirely  interrupted 
for  a  brief  interval,  then  commence  very  quietly,  gradually  in- 
creasing to  the  normal. 

Apnoaa  has  been  interpreted  in  two  ways.  Some  think  that 
it  is  due  to  fatigue  of  the  muscles  of  respiration  or  the  respira- 
tory center;  others  that  the  blood  has  under  these  circum- 
stances an  excess  of  oxygen,  which  so  influences  the  respiratory 
center  that  it  is  quieted  (inhibited)  for  a  time. 

The  latter  view  is  that  usually  adopted ;  but,  considering  that 
apncEa  results  from  the  sobbing  of  children  following  a  pro- 
longed fit  of  crying,  also  in  Cheyne-Stokes  and  other  abnormal 
forms  of  breathing,  and  that  the  blood  is  normally  almost  satu- 
rated with  oxygen,  it  will  be  agreed  that  there  is  a  good  deal 
to  be  said  for  the  first  view,  especially  that  part  of  it  which 
represents  the  cessation  of  breathing  as  owing  to  excessive 
activity  and  exhaustion  of  the  respiratory  center.  We  find 
such  a  calm  in  asphyxia  after  the  convulsive  storm. 

Is  it,  then,  the  excessive  accumulation  of  carbon  dioxide  or 
the  deficiency  of  oxygen  that  induces  dyspnoea  ?  Considering 
that  the  former  gas  acts  as  a  narcotic,  and  does  not  induce  con- 
vulsions, even  when  it  constitutes  a  large  percentage  of  the 
atmosphere  breathed,  and  that  the  need  of  oxygen  for  the  tis- 
sues is  constant,  it  certainly  seems  most  reasonable  to  conclude 
that  the  phenomena  of  dyspnoea  are  owing  to  the  lack  of  oxy- 
gen chiefly,  at  least ;  though  the  presence  of  an  excess  of  car- 
bonic anhydride  may  take  some  share  in  arousing  that  vigorous 
effort  on  the  part  of  the  nervous  system,  to  restore  the  func- 
tional equilibrium,  so  evident  under  the  circumstances. 

The  Cheyne-Stokes  Respiration  (Phenomenon). — There  is  a  form 
of  breathing  occurring  under  a  variety  of .  abnormal  circum- 
stances, in  which  the  respirations  gradually  reach  a  maximum 
(dyspnoea),  and  then  as  gradually  decline  to  absolute  cessation 
(apnoea).  The  pause  may  last  a  surprising  length  of  time  (one 
half  to  three  quarters  of  a  minute),  when  this  form  of  breathing 
again  repeats  itself.  It  has  been  compared  to  the  periodic 
grouping  of  heart-beats  (Luciani  groups),  occurring  when  the 
organ  is  suffering.  There  is  abundant  cause  usually  for  ex- 
haustion of  the  center,  on  account  of  disordered  blood  or  an 
insufficient  supply  to  the  brain.  This  phenomenon  and  apnoea 
bring  out  clearly  the  rhythmic  character  of  those  processes. 


THE  RESPIRATORY  SYSTEM.  399 

like  respiration,  which  in  the  nature  of  the  case  must  be  in 
the  higher  groups  of  vertebrates  ceaseless,  and  it  is  not  surpris- 
ing that,  like  a  lame  dog,  which  prefers  progression  by  three 
legs  to  none  at  all,  the  ever-active  center  will  keep  up  its  rhythm 
as  long  as  it  can — perfectly,  if  possible,  and,  if  not  perfectly,  as 
well  as  it  can.  We  mean  to  imply  that  its  action  must  be 
rhythmic,  or  cease  entirely. 

The  Effects  of  Variations  in  the  Atmospheric 
Pressure. 

These  depend  in  great  part  upon  the  suddenness  with  which 
the  change  is  made.  When  an  individual  ascends  a  high 
mountain  or  rises  in  a  balloon,  parts  in  contact  with  the  air 
become  reddened  and  swollen,  owing  to  the  distention  of  the 
small  vessels,  which  may  result  in  hsemorrhages.  There  is  dif- 
ficulty in  breathing,  the  respirations  become  more  rapid,  as  also 
the  pulse.  If  the  lowering  of  pressure  amounts  to  from  one 
third  to  one  half,  the  quantity  of  oxygen  in  the  blood  is  dimin- 
ished, and  the  carbon  dioxide  imperfectly  excreted.  Owing  to 
the  excess  of  blood  in  the  superficial  parts,  the  internal  organs 
become  anaemic,  and  there  is  consequently  diminished  secretion 
of  urine  and  a  variety  of  other  disturbances,  with  general  weak- 
ness.    The  blood-pressure  is  also  altered. 

Sudden  diminution  of  pressure  gives  rise  to  a  liberation  of 
gas — chiefly  nitrogen — within  the  blood-vessels,  which  causes 
death  by  blocking  the  circulation  in  the  small  vessels  (hence 
also  the  danger  from  section  of  a  large  vein  in  surgical  opera- 
tions about  the  neck,  the  air  being  liable  to  be  sucked  in,  owing 
to  the  negative  pressure). 

Increase  in  the  atmospheric  pressure  when  not  very  great 
gives  rise  to  symptoms  akin  to  those  of  narcotic  poisoning; 
but  when  the  increase  amounts  to  twenty  atmospheres,  animals 
die,  as  if  asphyxiated,  with  convulsions.  Neither  the  assump- 
tion of  oxygen  nor  tlie  separation  of  carbon  dioxide  takes  place 
to  the  usual  extent ;  and  it  is  interesting  to  note  that  micro- 
organisms are  killed  under  similar  circumstances. 

Witli  considerable  diminution  of  pressure,  though  not  suf- 
ficient to  lead  to  a  fatal  result,  symptoms  the  opposite  of  those 
describofl  above  occur.  Thus,  there  is  paleness  of  the  surface, 
respiration  is  easy,  the  capacity  of  the  lungs  is  increased,  owing, 
it  is  thought,  to  the  greater  descent  of  the  diaphragm,  in  con- 
sef^uence  of  the  compression  of  the  gases  of  the  intestines. 


400 


ANIMAL  PHYSIOLOGY. 


Urine  is  secreted  in  excess,  there  is  more  muscular  energy,  and 
the  metabolism  of  the  body  generally  is  accelerated.  Air  under 
altered  pressure  has  been  employed  as  a  therapeutic  agent,  but 
a  little  reflection  will  make  it  clear  that  it  is  a  remedy  to  be 
used  with  the  greatest  care,  especially  when  there  is  disease  of 
the  heart,  blood-vessels,  etc. 

The  Influence  of  Respiration  on  the  Circulation. 

An  examination  of  tracings  of  the  intra-thoracic  and  blood- 
pressure,  taken  simultaneously,  shows  (1)  that  during  inspira- 
tion the  blood-pressure  rises  and  the  intra-thoracic  pressure 
falls ;  (2)  that  during  expiration  the  reverse  is  true ;  and  (3)  that 
the  heart-beat  is  slowed,  and  has  a  decided  effect  on  the  form 
of  the  pulse.  But  it  also  appears  that  the  period  of  highest 
blood-pressure  is  just  after  expiration  has  begun. 


Fig.  319.-  Tracin^.s  of  blood-pressure  and  intrathoracic  pressure  (after  Foster),  a,  blood- 
pressure  tracing  showing  irregularities  due  to  respiration  and  pulse  :  6,  curve  of  intra- 
thoracic pressure  ;  /,  beginning  of  inspiration  ;  e,  of  expiration.  Intrathoracic  pressure 
is  seen  to  rise  rapidly  after  inspiration  ceases,  and  then  slowly  sinlis  as  the  expiratory 
blast  continues,  to  become  a  rapid  faU  when  inspiration  begins. 

We  must  now  attempt  to  explain  how  these  changes  are 
brought  about.  By  intra-thoracic  pressure  is  meant  the  press- 
ure the  lungs  exert  on  the  costal  pleura  or  any  organ  within 
the  chest,  which  must  differ  from  intra-pulmonary  pressure 
and  the  pressure  of  the  atmosphere,  because  of  the  resistance 
of  the  lungs  by  virtue  of  their  own  elasticity. 

It  has  been  noted  that  even  in  death  the  lungs  remain  par- 
tially distended ;  and  that  when  the  thorax  is  opened  the  pul- 
monary collapse  which  follows  demonstrates  that  their  elas- 
ticity amounts  to  about  five  millimetres  of  mercury,  which 
must,  of  course,  represent  but  a  small  portion  of  that  elasticity 
which  may  be  brought  into  play  when  these  organs  are  greatly 
distended,  so  that  they  never  press  on  the  costal  walls,  heart. 


THE  RESPIRATORY  SYSTEM.  401 

etc.,  witli  a  pressure  equal  to  that  of  the  atmosphere.  It  follows 
that  the  deeper  the  inspiration  the  greater  the  difference  be- 
tween the  intra-thoracic  and  the  atmospheric  pressure.  Even 
in  exi^iration,  except  when  forced,  the  intra-thoracic  pressure 
remains  less,  for  the  same  reason. 

These  conditions  must  have  an  influence  on  the  heart  and 
blood-vessels.  Bearing  in  mind  that  the  pressure  without  is 
practically  constant  and  always  greater  than  that  within  the 
thorax,  the  conditions  are  favorable  to  the  flow  of  blood  toward 
the  heart.  As  in  inspiration,  the  pressure  on  the  great  veins 
and  the  heart  is  diminished,  and,  as  these  organs  are  not  rigid, 
they  tend  to  expand  within  the  thorax,  thus  favoring  an  on- 
ward flow.  But  the  opposite  effect  would  follow  as  regards  the 
large  arteries.  Their  expansion  must  tend  to  withdraw  blood. 
During  expiration  the  conditions  are  reversed.  The  effects  on 
the  great  veins  can  be  observed  by  laying  them  bare  in  the 
neck  of  an  animal,  when  it  may  be  seen  that  during  inspiration 
they  become  partially  collapsed,  and  refilled  during  expiration. 
In  consequence  of  the  marked  thickness  of  the  coats  of  the 
great  arteries,  the  effect  of  changes  in  intra-thoracic  pressure 
must  be  slight.  The  comparatively  thin-walled  auricles  act 
somewhat  as  the  veins,  and  it  is  likely  that  the  increase  of 
pressure  during  expiration  must  favor,  so  far  as  it  goes,  the 
cardiac  systole. 

More  blood,  then,  entering  the  right  side  of  the  heart  dur- 
ing inspiration,  more  will  be  thrown  into  the  systemic  circula- 
tion, unless  it  be  retained  in  the  lungs,  and,  unless  the  effect  be 
counteracted,  the  arterial  pressure  will  rise,  and,  as  all  the  con- 
ditions are  reversed  during  expiration,  we  look  for  and  find 
exactly  opposite  results.  The  lungs  themselves,  however,  must 
be  taken  into  the  account.  During  inspiration  room  is  pro- 
vided for  an  increased  quantity  of  blood,  the  resistance  to  its 
flow  is  lessened,  hence  more  blood  reaches  the  left  side  of  the 
heart.  The  immediate  effect  would  be,  notwithstanding,  some 
diminution  in  the  quantity  flowing  to  the  left  heart,  in  conse- 
quence of  the  sudden  widening  of  the  pulmcmary  vessels,  the 
reverse  of  which  would  follow  during  expiration;  hence  the 
period  of  highest  intra-thoracic  pressure  is  after  the  onset  of 
the  expiratory  act.  During  inspiration  the  descent  of  the  dia- 
phragm compressing  tlie  ,'i})dorninal  organs  is  thought  to  force 
on  blood  from  the  abdominal  veins  int(j  the  th(jracic  vena  cava. 

That  the  respiratory  movements  do  exert  in  some  way  a 
pronounced  effect  on  the  circulation  the  student  may  demon- 

26 


402  ANIMAL  PHYSIOLOGY. 

strate  to  himself  in  the  following  ways  :  1.  After  a  full  inspira- 
tion, close  the  glottis  and  attempt  to  expire  forcibly,  keeping 
the  fingers  on  the  radial  artery.  It  may  he  noticed  that  the 
pulse  is  modified  or  possibly  for  a  moment  disappears.  2.  Re- 
verse the  experiment  by  trying  to  inspire  forcibly  with  closed 
glottis  after  a  strong  expiration,  when  the  pulse  will  again  be 
found  to  vary.  In  the  first  instance,  the  heart  is  comparative- 
ly empty  and  hampered  in  its  action,  intra-thoracic  pressure 
being  so  great  as  to  prevent  the  entrance  of  venous  blood  by 
compression  of  the  heart  and  veins,  while  that  already  within 
the  organ  and  returning  to  it  from  the  lungs  soon  passes  on 
into  the  general  system,  hence  the  pulseless  condition.  The 
explanation  is  to  be  reversed  for  the  second  case.  The  heart's 
beat  is  modified,  probably  reflexly,  through  the  cardio-inhibitory 
center,  for  the  changes  in  the  pulse-rate  do  not  occur  when  the 
vagi  nerves  are  cut,  at  least  not  to  nearly  the  same  extent. 

Comparative. — It  may  be  stated  that  the  cardiac  phenomena 
referred  to  in  this  section  are  much  more  marked  in  some  ani- 
mals than  in  others.  Very  little  change  may  be  observed  in 
the  pulse-rate  in  man,  while  in  the  dog  it  is  so  decided  that  one 
observing  it  for  the  first  time  might  suppose  that  such  pro- 
nounced irregularity  of  the  heart  was  the  result  of  disease ; 
though  even  in  this  animal  there  are  variations  in  this  respect 
with  the  breed,  age,  etc. 

We  must  now  direct  attention  to  certain  facts  which  have 
been  very  differently  interpreted. 

During  artificial  respiration,  when  air  is  pumped  into  the 
chest  by  a  bellows,  it  follows,  of  course,  that  all  the  usual  press- 
ure conditions  are  reversed — e.  g.,  the  inspiratory  pressure  is 
greater  than  the  expiratory. 

If  artificial  respiration,  in  an  animal  under  experiment,  be 
stopped,  it  may  be  noticed  that  there  is  at  first  a  steady  rise  of 
blood-pressure ;  but  presently  certain  undulations  in  the  respir- 
atory tracings  may  be  observed,  known  as  Traube-Hering 
curves ;  and  these  will  appear  even  when  the  vagi  nerves  are 
cut,  and  disappear  only  with  the  fall  of  blood-pressure  that 
ensues  with  the  exhaustion  of  the  animal. 

If  the  spinal  cord  has  been  divided,  the  tracings  may  still 
be  obtained,  though  the  effect  is  not  so  marked.  These  are  the 
phenomena,  but  there  is  much  divergence  of  opinion  as  to  their 
cause.  Some  maintain  that  mechanical  effects  suffice  to  explain 
them,  though  the  majority  are  not  of  this  opinion,  but  believe 
them  due  to  rhythmical  variations  in  the  caliber  of  the  arteri- 


THE  RESPIRATORY  SYSTEM. 


403 


oles  affected  through,  vaso-motor  nerves  in  obedience  to  the 
medullary  center  which  operates  by  their  agency;    and  that 


Fig.  320. — Tracings  of  blood-pressure  in  rabbit  to  show  Traube-Hering  curves  (after  Foster). 
The  widest  undulations  indicate  Traube  Hering  curves  ;  those  next  in  size,  effects  of 
respiration  ;  and  the  smallest,  of  the  pulse. 

when  this  center  is  disabled  its  subordinates  in  the  spinal  cord 
take  upon  them  the  task.  It  has  also  been  suggested  that  there 
may  be  a  local  vaso-motor  mechanism  acted  upon  by  the  ve- 
nous blood  or  that  the  muscle-cells  themselves  may  be  influ- 
enced by  the  unnatural  condition  of  the  blood  in  asphyxia. 

These  curves,  however,  also  appear  during  respiration  that 
deviates  but  little  from  the  normal. 

It  is  to  be  borne  in  mind  that  the  tracings  on  which  we 
have  based  our  reasoning  do  not  represent  what  takes  place  in 
every  mode  of  breathing.  The  subject  is  one  of  great  com- 
y)lexity.  Doubtless  mechanical  explanations  go  a  long  way 
here,  but  they  are  so  mixed  up  with  factors  that  play  a  part 
more  or  less  prominent,  though  difficult  to  isolate  in  individual 
instances,  and  in  no  wise  to  be  explained  as  other  than  vital 
effects,  that  one  must  exercise  the  usual  caution ;  the  more  no 
as  it  is  found  upon  actual  experiment  that  the  outcome,  as 
regards  blood-pressure,  is  not  always  quite  what  would  have 
been  expected,  reasoning  from  the  principles  of  physics  alone. 

That  there  are  rhythms  within  rhythms  in  the  vascular  and 
respiratory  system,  rendering  the  subject  complex  beyond  the 
power  of  experiments  fully  to  unravel,  is  a  conviction  that  we 
think  will  deepen  in  the  minds  of  physiologists. 


404  ANIMAL  PHYSIOLOGY. 

The  Respiration  and  Circulation  in  Asphyxia. — A  most  instruct- 
ive experiment  may  be  arranged  thus : 

Let  an  ansestlietized  rabbit,  cat,  or  sucb-like  animal,  have 
tlie  carotid  of  one  side  connected  with  a  glass  tube  as  before 
described  (page  229),  by  which  the  blood-pressure  and  its 
changes  may  be  indicated,  and,  when  the  normal  respiratory 
acts  have  been  carefully  observed,  proceed  to  notice  the  effects 
on  the  blood-pressure,  etc.,  of  pumping  air  into  the  chest  by  a 
bellows,  of  hindering  the  ingress  of  air  to  a  moderate  degree, 
and  of  struggling.  With  a  small  animal  it  will  be  difficult  to 
observe  the  respiratory  effects  on  the  blood-pressure  by  simply 
watching  the  oscillations  of  the  fluid  in  the  glass  tube,  but  this 
is  readily  enough  made  out  if  more  elaborate  arrangements  be 
made,  so  that  a  graphic  tracing  may  be  obtained. 

But  the  main  events  of  asphyxia  may  be  well  (perhaps  best) 
studied  in  this  manner  : 

Let  the  trachea  be  occluded  (ligatured).  At  once  the  blood- 
pressure  will  be  seen  to  rise  and  remain  elevated  for  some  time, 
then  gradually  fall  to  zero.  These  changes  are  contemporane- 
ous with  a  series  of  remarkable  manifestations  of  disturbance 
in  the  respiratory  system  as  it  at  first  appears,  but  in  reality' 
due  to  wide-spread  and  profound  nutritive  disturbance.  So  far 
as  the  breathing  is  concerned,  it  may  be  seen  to  become  more 
rapid,  deeper,  and  labored,  in  which  the  expiratory  phase  be- 
comes more  than  proportionably  marked  (dyspnoea) ;  this  is  fol- 
lowed by  the  gradual  action  of  other  muscles  than  those  usually 
employed  in  respiration,  until  the  whole  body  passes  into  a  ter- 
rible convulsion — a  muscle-storm  in  consequence  of  a  nerve- 
storm.  When  this  has  lasted  a  variable  time,  but  usually 
about  one  minute,  there  follows  a  period  of  exhaustion,  during 
which  the  subject  of  the  experiment  is  in  a  motionless  condi- 
tion, interrupted  by  an  occasional  respiration,  in  which  inspi- 
ration is  more  pronounced  than  expiration ;  and,  finally,  the 
animal  quietly  stretches  every  limb,  the  sphincters  are  relaxed, 
there  may  be  a  discharge  of  urine  or  faeces  from  peristaltic 
movements  of  the  bladder  or  intestines,  and  death  ends  a  strik- 
ing scene.  These  events  may  be  classified  in  three  stages, 
though  the  first  and  second  especially  merge  into  one  another : 
1.  Stage  of  dyspnoea.  2.  Stage  of  convulsions.  3.  Stage  of 
exhaustion. 

It  is  during  the  first  two  stages  that  the  blood-pressure  rises, 
and  during  the  third  that  it  sinks,  due  in  the  first  instance 
chiefly  to  excessive  activity  of  the  vaso-motor  center,  and  in 


THE  RESPIRATORY  SYSTEM.  405 

the  second  to  its  exhaustion  and  the  weakening  of  the  heart- 
beat. 

These  violent  movements  are  owing,  we  repeat,  to  the  action 
of  blood  deficient  in  oxygen  on  the  respiratory  center  (or  cen- 
ters), leading  to  inordinate  action  followed  by  exhaustion. 

The  duration  of  the  stages  of  asphyxia  varies  with  the  ani- 
mal, but  rarely  exceeds  five  minutes.  In  this  connection  it  may 
be  noted  that  newly-born  animals  (kittens,  pupj^ies)  bear  im- 
mersion in  water  for  as  much  as  from  thirty  to  fifty  minutes, 
while  an  adult  dog  dies  within  four  or  five  minutes.  This  is 
to  be  explained  by  the  feeble  metabolism  of  new-born  mam- 
mals, which  so  slowly  uses  up  the  vital  air  (oxygen). 

If  the  chest  of  an  animal  be  opened,  though  the  respiratory 
muscles  contract  as  usual  there  is,  of  course,  no  ventilation  of 
the  lungs,  which  lie  collapsed  in  the  chest;  and  the  animal  dies 
about  as  quickly  as  if  its  trachea  were  occluded.  It  passes 
through  all  the  phases  of  asphyxia  as  in  the  former  case ;  but 
additional  information  may  be  gained.  The  heart  is  seen  to 
beat  at  first  more  quickly  and  forcibly,  later  vigorously  though 
slower,  and  finally  both  feebly  and  irregularly,  till  the  ventri- 
*  cles,  then  the  left  auricle,  and  finally  the  right  auricle  cease  to 
beat  at  all  or  only  at  long  intervals.  The  terminations  of  the 
great  veins  (representing  the  sinus  venosus)  beat  last  of  all. 

At  death  the  heart  and  great  veins  are  much  distended 
with  blood,  the  arteries  comparatively  empty.  Even  after 
rigor  mortis  has  set  in,  the  right  heart  is  still  much  engorged. 

These  phenomena  are  the  result  of  the  operation  of  several 
causes.  The  increasingly  venous  blood  at  first  stimulates  the 
heart  probably  directly,  in  j^art  at  least,  but  later  has  the  con- 
trary effect.  The  nutrition  of  the  organ  suffers  from  the  de- 
graded blood,  from  which  it  must  needs  derive  its  supplies. 
The  cardio-inhibitory  center  prol^ably  has  a  large  share  in  the 
-lowing  of  the  heart,  if  not  also  in  (quickening  it.  Wliether 
the  accelerator  fibers  of  the  vagus  or  synipathetic  jjlay  any 
part  is  uncertain.  The  increase  of  peripheral  resistance  caused 
by  the  action  of  the  vaso-motor  center  makes  it  more  difficult 
for  the  heart  to  empty  its  left  side  and  thus  receive  the  venous 
blood  as  it  pours  on.  At  the  same  time  the  deep  inspirations 
(when  the  chest  is  unopened)  favor  the  onflow  of  venous  blood; 
and  in  any  case  the  whole  venous  system,  including  the  right 
heart,  tends  to  become  engorged  from  these  several  causes  act- 
ing together.  The  heart  gives  up  the  struggle,  unable  to  main- 
tain it,  Ijut  not  so  long  as  it  can  beat  in  any  pai't. 


4:06  ANIMAL  PHYSIOLOGY. 

The  share  whicli  the  elasticity  of  the  arteries  takes  in 
forcing  on  the  blood  when  the  heart  ceases,  and  the  contraction 
of  the  muscular  coat  of  these  vessels,  especially  the  smaller, 
must  not  be  left  out  of  the  account  in  explaining  the  phenom- 
ena of  asphyxia  and  the  post-mortem  appearances. 

Pathological. — The  importance  of  being  practically  as  well  as 
theoretically  acquainted  with  the  facts  of  asphyxia  is  very  great. 

The  appearance  of  the  heart  and  venous  system  gives  une- 
quivocal evidence  as  to  the  mode  of  death  in  any  case  of  as- 
phyxia ;  and  the  contrast  between  the  heart  of  an  animal  bled 
to  death,  or  that  has  died  of  a  lingering  disease,  and  one 
drowned,  hanged,  or  otherwise  asphyxiated,  is  extreme. 

We  strongly  recommend  the  student  to  asphyxiate  some 
small  mammal  placed  under  the  influence  of  an  anaesthetic, 
and  to  note  the  phenomena,  preferably  with  the  chest  opened  ; 
and  to  follow  up  these  observations  by  others  after  the  onset 
of  rigor  mortis. 

Peculiar  Respiratory  Movements. 

Though  at  first  sight  these  seem  so  different,  and  are  so  as 
regards  acts  of  expression,  yet  from  the  respiratory  point  of 
view  they  resemble  each  other  closely;  they  are  all  reflex, 
and,  of  course,  involuntary.  Many  of  them  have  a  common 
purpose,  either  the  better  to  ventilate  the  lungs,  to  clear  them 
of  foreign  bodies,  or  to  prevent  their  ingress. 

Coughing,  in  which  such  a  purpose  is  evident,  is  made  up  of 
several  expiratory  efforts  preceded  by  an  inspiratory  act.  The 
afferent  nerve  is  usually  the  vagus  or  laryngeal,  but  may  be 
one  or  more  of  several  others. 

The  glottis  presents  characteristic  appearances,  being  closed 
and  then  opened  suddenly,  the  mouth  being  kept  open. 

Coughing  is  often  induced  in  attempting  to  examine  the  ear 
with  instruments.     (Reflex  act.) 

Laughing  is  very  similar  to  the  last,  so  far  as  the  behavior 
of  the  glottis  is  concerned,  though  it  usually  acts  more  rapidly, 
of  course.     Several  expirations  follow  a  deep  inspiration. 

Crying  is  essentially  the  same  as  laughing,  but  the  facial 
expression  is  different,  and  the  lachrymal  gland  functions  exces- 
sively, though  with  some  persons  this  occurs  during  laughter 
also. 

Sobbing  is  made  up  of  a  series  of  inspirations,  in  which  the 
glottis  is  partially  closed,  followed  by  a  deep  expiration. 


THE   RESPIRATORY  SYSTEM.  407 

Yawning  involves  a  deep-drawn,  slow  inspiration,  followed 
by  a  more  sudden  expiration,  with  a  well-known  depression  of 
the  lower  jaw  and  usually  stretching  movements. 

Sighing  is  much  like  the  preceding,  though  the  mouth  is  not 
opened  widely  if  at  all,  nor  do  the  stretching  movements  com- 
monly occiir. 

Hiccough  is  produced  by  a  sudden  inspiratory  effort,  though 
fruitless,  inasmuch  as  the  glottis  is  suddenly  closed.  It  is 
spoken  of  as  spasm  of  the  diaphragm,  and  when  long  continued 
is  very  exhaustive. 

Sneezing  is  the  result  of  a  powerful  and  sudden  expiratory 
act  following  a  deep  inspiration,  the  mouth  being  usually  closed 
by  the  anterior  pillars  of  the  fauces  against  the  outgoing  cur- 
rent of  air,  which  then  makes  its  exit  through  the  nose,  while 
the  glottis  is  forcibly  opened  after  sudden  closure.  It  will  be 
noticed  that  in  most  of  these  acts  the  glottis  is  momentarily 
closed,  which  is  never  the  case  in  mammals  during  quiet  res- 
piration. 

This  temporary  occlusion  of  the  respiratory  passages  per- 
mits of  a  higher  intrapulmonary  pressure,  which  is  very  effect- 
ive in  clearing  the  passages  of  excess  of  mucus,  etc.,  when  the 
glottis  is  suddenly  opened.  Though  the  acts  described  are  all 
involuntary,  they  may  most  of  them  be  imitated  and  thus 
studied  deliberately  by  the  student.  It  will  also  appear,  con- 
sidering the  many  ways  in  which  some  if  not  all  of  them  may 
be  brought  about,  that  if  the  medullary  center  is  responsible 
for  the  initiation  of  them,  it  must  be  accessible  by  numberless 
paths. 

Comparative. — Few  of  the  lower  animals  cough  with  the  same 
facility  as  man,  while  laughing  is  all  but  unknown,  crying  and 
sobbing  rare,  though  the  whining  of  dogs  is  allied  to  the  cry- 
ing of  human  beings. 

Sneezing  seems  to  be  voluntary  in  some  animals,  as  squir- 
rels, when  engaged  in  toilet  operations,  etc. 

Barking  is  voluntary,  and  in  mechanism  resembles  cough- 
ing, the  vocal  cords  being,  however,  more  definitely  employed, 
as  also  in  growling. 

Bawling,  neighing,  braying,  etc.,  are  made  up  of  long  expira- 
tory acts,  preceded  by  one  or  more  inspirations.  The  vocal 
cords  are  also  rendered  tense. 


408  ANIMAL  PHYSIOLOGY. 

Special.  Considerations. 

Pathological  and  Clinical. — The  number  of  diseases  that  lessen 
the  amount  of  available  pulmonary  tissue,  or  hamper  the  move- 
ments of  the  chest,  are  many,  and  only  the  briefest  reference 
can  be  made  to  a  few  of  them. 

Inflammation  of  the  lungs  may  render  a  greater  or  less  por- 
tion of  one  or  both  lungs  solid ;  inflammation  of  the  pleura 
(pleuritis,  pleurisy)  by  the  dryness,  pain,  etc.,  may  restrict  the 
thoracic  movements;  philiisis  may  solidify  or  excavate  the  lungs, 
or  by  pleuritic  inflammation  glue  the  costal  and  pulmonary 
pleural  surfaces  together ;  bronchitis  clog  the  tubes  and  other 
air-passages  with  altered  secretions ;  emiDliysema  (distention  of 
air-cells)  may  destroy  elasticity  of  parts  of  the  lung ;  pneuma- 
tliorax  from  rupture  of  the  lung-tissue  and  consequent  accumu- 
lation of  gases  in  the  pleural  cavity,  or  pleurisy  with  effusion, 
render  one  lung  all  but  useless  from  pressure.  In  all  such 
cases  Nature  attempts  to  make  up  what  is  lost  in  amplitude  by 
increase  in  rai3idity  of  the  respiratory  movements.  It  is  inter- 
esting to  note  too  how  the  other  lung,  in  diseased  conditions,  if 
it  remain  unaffected,  enlarges  to  compensate  for  the  loss  on  the 
opposite  side.  When  the  muscles  are  weak,  especially  if  there 
be  hindrance  to  the  entrance  of  air  while  the  thoracic  move- 
ments are  marked,  there  may  be  bulging  inward  of  the  inter- 
costal spaces. 

Normally,  this  would  also  occur,  as  the  intra-thoracic  press- 
ure is  less  than  the  atmospheric,  were  it  not  for  the  fact  that 
the  intercostal  muscles  when  contracting  have  a  certain  resist- 
ing power. 

The  imperfect  respiration  of  the  moribund,  permitting  the 
accumulation  of  carbonic  anhydride  with  its  soporific  effects, 
smooths  the  descent  into  the  valley  of  the  shadow  of  death ;  so 
that  there  may  be  to  the  uninitiated  the  appearance  of  a  suffer- 
ing which  does  not  exist,  consciousness  itself  being  either 
wholly  or  partially  absent.  The  dyspnoea  of  anaemic  persons, 
whether  from  sudden  loss  of  blood  or  from  imperfect  renewal 
of  the  haemoglobin,  shows  that  this  substance  has  a  respiratory 
function ;  while  in  forms  of  cardiac  disease  with  regurgitation, 
etc.,  the  blood  may  be  imperfectly  oxidized,  giving  rise  to  la- 
bored respiration. 

Personal  Observation. — As  hinted  from  time  to  time  during 
the  treatment  of  this  subject,  there  is  a  large  number  of  facts 
the  student  may  verify  for  himself. 


THE   RESPIRATORY  SYSTEM.  409 

A  simple  way  of  proving  that  COo  is  exhaled  is  to  breathe 
(blow)  into  a  vessel  containing  some  clear  solution  of  quick- 
lime (CaO),  the  turbidity  showing  that  an  insoluble  salt  of  lime 
(CaCOs)  has  been  formed  by  the  addition  of  this  gas. 

The  functions  of  most  of  the  respiratory  muscles,  the  phe- 
nomena of  dyspnoea,  apnoea  (by  a  series  of  long  breaths),  partial 
asphyxia  by  holding  the  breath,  and  many  other  experiments, 
simjDle  but  convincing,  will  occur  to  the  student  who  is  willing 
to  learn  in  this  way. 

The  observation  of  respiration  in  a  dreaming  animal  (dog) 
will  show  how  mental  occurrences  affect  the  respiratory  center 
in  the  absence  of  all  the  usual  outward  influences.  The  respira- 
tion of  the  domestic  animals,  of  the  frog,  turtle,  snake,  and  fish 
are  easily  watched  if  these  cold-blooded  animals  be  placed  for 
observation  beneath  a  glass  vessel.  Their  study  will  teach  how 
manifold  are  the  ways  by  which  the  one  end  is  attained.  Com- 
pare the  tracings  of  Fig.  313. 

Evolution. — A  study  of  embryology  shows  that  the  respira- 
tory and  circulatory  systems  develoi3  together;  that  the  vascu- 
lar system  functions  largely  as  a  respiratory  system  also  in  cer- 
tain stages,  and  remains  such,  from  a  physiological  point  of 
view,  throughout  embryonic  life. 

The  changes  that  take  place  in  the  vascular  system — the 
heart,  especially — of  the  mammal  when  the  lungs  have  become 
functionally  active  at  birth,  show  how  one  set  of  organs  modi- 
fies the  other. 

When  one  considers,  in  addition  to  these  facts,  that  the 
digestive  as  well  as  the  vascular  and  respiratory  organs  are 
represented  in  one  group  of  structures  in  a  jelly-fish,  and  that 
the  lungs  of  the  mammal  are  derived  from  the  same  mesoblast 
as  gives  rise  to  the  digestive  and  circulatory  organs,  many  of 
the  relations  of  these  systems  in  the  highest  groups  of  animals 
become  intelligible ;  but  unless  there  be  descent  with  modifica- 
tion, these  facts,  clear  enough  from  an  evolutionary  standpoint, 
are  isolated  and  out  of  joint,  bound  together  by  no  common 
principle  that  satisfies  a  philosophical  biology. 

It  has  been  found  that  in  hunting-dogs  and  wild  rabbits  the 
vagus  is  more  efficient  than  in  other  races  of  dogs  and  in  rab- 
bits kept  in  confinement ;  and  possibly  this  may  in  i)art  account 
for  the  greater  speed  and  especially  the  endurance  of  the 
former.  The  very  conformation  of  some  animals,  as  the  grey- 
hound, with  his  deep  chest  and  capacious  lungs,  indicates  an 
unusual  respiratory  capacity. 


410  ANIMAL   PHYSIOLOGY. 

The  laiv  of  habit  is  well  illustrated  in  the  case  of  divers,  who 
can  bear  deprivation  of  air  longer  than  those  unaccustomed  to 
such  submersion  in  water.  Greater  toleration  on  the  part  of 
the  respiratory  center  has  probably  much  to  do  with  the  case, 
though  doubtless  many  other  departures  from  the  normal  occur, 
either  independently  or  correlated  to  the  changes  in  the  respira- 
tory center. 

Summary  of  the  Physiology  of  Respiration. — The  purpose  of 
repiration  in  all  animals  is  to  furnish  oxygen  for  the  tissues 
and  remove  the  carbonic  anhydride  they  produce,  which  in  all 
vertebrates  is  accomplished  by  the  exposure  of  the  blood  in 
capillaries  to  the  atmospheric  air,  either  free  or  dissolved  in 
water.  A  membrane  lined  with  cells  always  intervenes  between 
the  capillaries  and  the  air. 

The  air  may  be  pumped  in  and  out,  or  sucked  in  and  forced 
out. 

Respiration  in  the  IVCammal. — The  air  enters  the  lungs,  owing 
to  the  enlargement  of  the  chest  in  three  directions  by  the  action 
of  certain  muscles.  It  leaves  the  lungs  because  of  their  own 
elastic  recoil  and  that  of  the  chest- wall  chiefly.  Inspiration  is 
active,  expiration  chiefly  passive. 

The  diaphragm  is  the  principal  muscle  of  respiration.  In 
some  animals  there  is  a  well-marked  facial  and  laryngeal  as 
well  as  thoracic  respiration.  Respiration  is  rhythmical,  con- 
sisting of  inspiration,  succeeded  without  appreciable  pause  by 
expiration,  the  latter  being  in  health  of  only  slightly  longer 
duration.  There  is  also  a  definite  relation  between  the  number 
of  respirations  and  of  heart-beats.  According  as  respiration  is 
normal,  hurried,  labored,  or  interrupted,  we  describe  it  as 
eupnoBa,  hyperpnoea,  dyspnoea,  and  ap7io&a.  The  intra-thoracic 
pressure  is  never  equal  to  the  atmospheric — i.  e.,  it  is  always 
negative — except  in  forced  expiration ;  and  the  lungs  are  never 
collapsed  so  long  as  the  chest  is  unopened.  The  expired  air 
differs  from  that  inspired  in  being  of  the  temperature  of  the 
body,  saturated  with  moisture,  and  containing  about  4  to  5 
per  cent  less  oxygen  and  4  per  cent  more  carbonic  anhydride, 
besides  certain  indifferently  known  bodies,  the  result  of  tissue 
metabolism,  excreted  by  the  lungs. 

The  quantity  of  air  actually  moved  by  a  respiratory  act,  as 
compared  with  the  total  capacity  of  the  respiratory  organs,  is 
small ;  hence  a  great  part  must  be  played  by  diffusion.  The 
portion  of  air  that  can  not  be  removed  from  the  lungs  by  any 
respiratory  effort  is  relatively  large. 


THE  KESPIRATORY  SYSTEM.  411 

It  is  customary  to  distinguish  tidal,  complementary,  supple- 
mentary, and  residual  air. 

The  vital  capacity  is  estimated  by  the  quantity  of  air  the 
respiratory  organs  can  move,  and  is  very  variable. 

The  blood  is  ilie  respiratory  tissue,  through  the  mediation 
of  its  red  cells,  by  the  haemoglobin  they  contain.  This  sub- 
stance is  a  ferruginous  proteid,  capable  of  crystallization,  and 
assuming  under  chemical  treatment  many  modifications.  When 
it  contains  all  the  oxygen  it  can  retain,  it  is  said  to  be  saturated, 
and  is  called  oxy -haemoglobin,  in  which  form  it  exists  (with 
some  reduced  haemoglobin)  in  arterial  blood,  and  to  a  lesser 
extent  in  venous  blood,  which  differs  from  arterial  in  the  rela- 
tive proportions  of  haemoglobin  (reduced)  it  contains,  as  viewed 
from  the  respiratory  standpoint. 

Oxy-haemoglobin  does  not  assume  or  part  with  its  oxygen, 
according  to  the  Henry-Dalton  law  of  pressures,  nor  is  this  gas 
in  a  state  of  ordinary  chemical  combination.  It  is  found  that 
the  oxygen  tension  of  the  blood  is  lower  and  that  of  carbonic 
anhydride  higher  than  in  the  air  of  the  alveoli  of  the  lungs, 
while  the  same  may  be  said  of  the  tissues  and  the  blood  re- 
spectively.    This  has  been,  however,  recently  again  denied. 

Respiration  is  a  vital  process,  though  certain  physical  con- 
ditions (temperature  and  pressure)  must  be  rigidly  maintained 
in  order  that  the  gaseous  interchanges  shall  take  place.  Res- 
piration is  always  fundamentally  bound  up  with  the  metabo- 
lism of  the  tissues  themselves.  All  animal  cells,  whether  they 
exist  as  unicellular  animals  (Amoeba)  or  as  the  components  of 
complex  organs,  use  up  oxygen  and  produce  carbonic  dioxide. 
Respiratory  organs,  usually  so  called,  and  the  respiratory  tissue 
par  excellence  (the  blood)  are  only  supplementary  mechanisms 
to  facilitate  tissue  respiration.  Carbonic  anhydride  exists  in 
blood  probably  in  combination  with  sodium  salts,  though  the 
whole  matter  is  very  obscure. 

Respiration,  like  all  the  other  functions  of  the  body,  is  con- 
trolled by  the  central  nervous  system  through  nerves.  The 
medulla  oblongata  is  chiefly  concerned,  and  esi)ecially  one 
small  part  of  it  known  as  the  respiratory  center.  It  is  possi- 
ble, even  probable,  that  there  are  subordinate  centers  in  the 
cord,  which,  under  peculiar  circumstances,  assume  importance; 
but  how  far  they  act  in  concert  with  the  medullary  center,  or 
wliether  they  act  at  all  when  normal  conditions  prevail,  is  an 
open  question. 

The  vagus  is  the  principal  afferent  respiratory  nerve.     The 


412  ANIMAL  PHYSIOLOGY. 

efferent  nerves  are  the  phrenics^  intercostals^  and  others  supply- 
ing the  various  muscles  used  in  moving  the  chest- walls,  etc. 

The  respiratory  center  is  automatic,  but  its  action  is  sus- 
ceptible of  modification  through  afferent  influences  taking  a 
variety  of  paths.  The  respiratory,  vaso-motor,  and  cardio- 
inhibitory  centers  seem  to  act  somewhat  in  concert. 

Blood-pressure  is  being  constantly  modified  by  the  respira- 
tory act,  rising  with  inspiration  and  sinking  with  expiration. 
In  some  animals  the  heart-beat  also  varies  with  these  phases 
of  respiration,  becoming  slow  and  irregular  during  expiration. 
Into  the  causation  of  these  changes  both  mechanical  and  nerv- 
ous factors  enter,  and  make  a  very  complex  mesh,  which  we 
can  at  present  but  imperfectly  unravel.  When  the  access  of 
air  to  the  tissues  is  prevented,  a  series  of  stages  of  respiratory 
activity  and  decline,  accompanied  by  pronounced  changes  in 
the  vascular  system,  are  passed  through,  known  as  asphyxia. 

Three  stages  are  distinguishable:  one  of  dyspnoea,  one  of 
convulsions,  and  one  of  exhaustion — while  at  the  same  time 
there  is  a  rise  of  blood-pressure  during  the  first  two,  and  a 
decline  during  the  third,  accompanied  by  marked  alterations  in 
the  cardiac  rhythm. 


PROTECTIVE  AND  EXCRETORY  FUNCTIONS  OF  THE  SKIN. 

As  has  been  intimated  from  time  to  time,  thus  far,  as  a 
result  of  the  metabolism  of  the  tissues,  certain  products  require 
constant  removal  from  the  blood  to  prevent  poisonous  effects. 
These  substances  are  in  all  probability  much  more  numerous 
than  physiological  chemistry  has  as  yet  distinctly  recognized 
or,  at  all  events,  isolated.  Quantitatively  considered,  the  most 
important  are  carbonic  anhydride,  water,  urea,  and,  of  less  im- 
portance, perhaps,  certain  salts. 

In  many  invertebrates  and  in  all  vertebrates  several  organs 
take  ]part  in  this  work  of  elimination  of  waste  products  or  puri- 
fication of  the  blood,  one  set  of  which — the  respiratory — we 
have  just  studied ;  and  we  now  continue  the  consideration  of 
the  subject  of  excretion,  this  term  being  reserved  for  the  pro- 
cess of  separating  harmful  products  from  the  blood  and  dis- 
charging them  from  the  body. 

We  strongly  recommend  the  student  to  make  the  study  of 
excretion  comparative  in  the  sense  of  noting  how  one  organ 
engaged  in  the  process  supplements  another.     A  clear  under- 


PROTECTIVE   AND   EXCRETORY  FUNCTIONS  OF  THE  SKIN.   413 


standing  of  this  relation  even  to  details  makes  the  practice  of 
medicine  more  scientific  and  practically  effective,  and  gives 
physiology  greater  breadth. 

The  skin  has  a  triple  function :  it  is  protective,  excretory, 
sensory,  and,  we  may  add,  nutritive  (absorptive)  and  respira- 
tory, especially  in  some  groups  of  animals. 

As  a  sensory  organ,  the  skin  will  receive  attention  later. 
Protective  Function  of  the  Skin. — Comparative. — Among  many 
groups  of  i]i vertebrates  the  principal  use  of  the  exterior  cover- 
ing of  the  body  is  manifestly  protection.  Among  these  forms, 
an  internal  skeleton  being  absent,  the  exo-skeleton  is  developed 
externally,  and  serves  not  only  for  protection,  but  for  the  at- 
tachment of  muscles,  as  seen  in  crustaceans  and  insects.  But 
this  part  of  the  subject  is  too  large  for  detailed  treatment  in 

such  a  work  as  this.  Turning  to 
the  vertebrates,  we  see  scales, 
bony  plates,  feathers,  spines,  hair, 
etc.,  most  of  them  to  be  regarded 
as  modifications  of  the  epidermis, 
always  useful,  and  frequently  also 
ornamental. 

•  Primitive  man  was  probably 
much  more  hirsute  than  his  mod- 


P\.--^'- 


r-1 


'•I ; 


Fig.  322. 


Via.  321. 


Fio 


.  321.— Sudoriparous  glands.  1  x  20  f  Aftor  Sapp^y.)  1.  1,  epidermis;  2,2,  mucous  layer; 
3,  3,  papilla; ;  1,  4.  derma  ;  .'),  5,  subcutaneous  areolar  tissue  ;  (i,  0,  6,  (j,  sudoriparous 
glaiitls  ;  7.  7.  adir)ow  vesicles ;  H.  H,  e.xcretorj'  rliicts  in  derma  ;  9,  9,  excretory  ducts  divided, 
Fio.  322.  — Portion  of  slfin  of  palm  of  hand  aljout  one-half  an  inch  (12'7  mm.)  square.  1x4. 
r.Vfter  Sapfx^y.)  1,  li  1,  1,  openin«8  of  audoriferous  ducts;  2,  2,  2,  2,  grooves  between 
papillH'  -if  hkm. 

em  representative;  and,  though  Hk;  liuman  subject  is  at  pres- 
ent provided  with  a  skin  in  wliicli  j)rotective  functions  are  at 
their  lowest,  still  the  epidermis  does  serve  such  a  purpose,  as 


414 


ANIMAL  PHYSIOLOGY. 


all  have  some  time  realized  when  it  has  been  accidentally  re- 
moved by  blistering,  etc. 

Taking  the  structure  of  the  skin  of  man  as  representing  that 
of  mammals  generally,  certain  points  claim  attention  from  the 

physiologist.  Its  elastic- 
ity, the  failure  of  which 
in  old  age  accounts  for 
wrinkles  ;  its  epidermal 
covering,  made  up  of 
numerous  layers  of  cells  ; 
its  coiled  and  spiral- 
ly twisted  sudoriferous 
glands,  permitting  of 
movements  of  the  skin 
without  harm  to  these 
structures ;  its  hair-folli- 
cles and  associated  seba- 
ceous glands,  the  fatty 
secretion  of  which  keeps 
the  hair  and  the  skin  gen- 
erally soft  and  pliable. 

The  muscles  of  the 
skin,  which  either  move 
it  as  a  whole  or  erect  in- 
dividual hairs,  play  an 
important  part  in  modi- 
fying expression,  well 
seen  in  the  whole  canine 
tribe  and  many  others. 

There  are  several  mod- 
ifications of  the  sebaceous 
glands  that  furnish  high- 
ly odoriferous  secretions, 
as  in  the  civet  cat,  the 
skunk,  the  musk  -  deer, 
and  many  lower  verte- 
brates. In  some,  these 
are  protective  (skunk)  ; 
in  others,  though  they 
may  not  be  agreeable  to 
the  senses  of  man,  they  are  doubtless  attractive  to  the  females 
of  the  same  tribe,  and  are  to  be  regarded  as  important  in 
"  sexual  selection/'  being  often  confined  to  the  males  alone. 


Fig.  323.— Hair  and  hair-follicle  (after  Sappey).  1, 
root  of  hair  ;  2,  bulb  of  hair  ;  3,  internal  root- 
sheath  ;  5,  membrane  of  hair-follicle  ;  6,  external 
membrane  of  follicle  ;  7,  7,  muscular  bands  at- 
tached to  follicle  ;  8,  8,  extremities  of  bands  pass- 
ing to  skin  ;  9,  compound  sebaceous  gland,  with 
duct  (10)  opening  into  upper  third  of  follicle  :  11, 
simple  sebaceous  gland  ;  12,  opening  of  hair-fol- 
licle. 


PROTECTIVE  AND  EXCRETORY   FUNCTIONS  OF   THE  SKIN.  415 

Ear-wax  and  the  Meibomian  secretion  are  the  work  of  modi- 
fied sebaceous  ghmds ;  as  also  the  oil-glands  so  highly  developed 
in  birds,  especially  aquatic  forms,  of  which  these  creatures 
make  great  use  in  preserving  their  feathers  from  wetting. 

The  Excretory  Function  of  the  Skin. 

Sweating  in  man  has  been  studied  by  inclosing  the  greater 
part  of  the  body  or  a  single  limb  in  a  caoutchouc  or  other  form 
of  impermeable  covering  and  exposing  the  subject  to  various 
degrees  of  heat ;  but,  apart  from  errors  in  collecting,  weighing, 
etc.,  such  sweating  must  be  regarded  as  somewhat  abnormal. 

It  is  clear,  however,  that  the  quantity  of  matter  discharged 
through  the  skin  is  large — greater  than  by  the  lungs  (about  as 
7  to  11),  though  the  amount  is  very  variable,  depending  on 
the  degree  of  activity  of  other  related  excreting  organs,  as  the 
lungs  and  kidneys,  and  largely  upon  the  temperature  as  a 
physical  condition. 

When  the  watery  vapor  is  carried  off,  before  it  can  condense, 
the  perspiration  is  said  to  he  insensible  ;  when  small  droplets 
become  visible,  sensible.  As  to  whether  the  one  or  the  other 
is  predominant  will,  of  course,  depend  on  the  rapidity  of  re- 
newal of  the  air,  its  humidity,  and  its  temperature.  Apart 
from  the  temperature,  the  amount  of  sweat  is  influenced  by  the 
quality  and  quantity  of  food  and,  especially,  of  drink  taken, 
the  amount  of  exercise,  and  psychic  conditions ;  not  to  speak 
of  the  effect  of  drugs,  poisons,  or  disease. 

Perspiration  in  man  is  a  clear  fluid,  mostly  colorless,  with 
a  characteristic  odor,  devoid  of  morphological  elements  (except 
epidermal  scales),  and  alkaline  in  reaction.  It  may  be  acid 
from  the  admixture  of  the  secretion  of  the  sebaceous  glands. 

Its  solids  (less  than  3  per  cent)  consist  of  sodium  salts, 
mostly  chlorides,  cholesterin,  neutral  fats,  and  traces  of  urea. 
The  acids  of  the  sweat  belong  to  the  fatty  series  (acetic,  buty- 
ric, formic,  propionic,  caprylic,  caproic,  etc.). 

Pathological. — The  sweat  may  contain  blood,  proteids,  abun- 
dance of  urea  (in  cholera),  uric  acid,  oxalates,  sugar,  lactic  acid, 
bile,  indigo  and  other  pigments.  Many  medicines  are  elimi- 
nated in  part  through  the  skin. 

Eespiration  by  the  Skin. — Comparative. — In  reptiles  and  batra- 
chiaiis,  with  smooth,  iiHjist  skin,  tli(;  respiratory  functi<ms  of 
this  organ  are  of  great  importance;  hence  these  animals  can 
live  long  under  water. 


416  ANIMAL  PHYSIOLOGY. 

It  is  estimated  that  in  the  frog  the  greater  part  of  the  car- 
bonic anhydride  of  the  body- waste  is  eliminated  by  the  skin. 
Certainly  frogs  can  live  for  days  immersed  in  a  tank  supplied 
with  running  water ;  and  it  is  a  significant  fact  that  in  this 
animal  the  vessel  that  gives  rise  to  the  pulmonary  artery  sup- 
plies also  a  cutaneous  branch. 

The  respiratory  capacity  of  the  skin  in  man  and  most  mam- 
mals is  comparatively  small  under  ordi7iary  circumstances. 
The  amount  of  carbonic  9.nhydride  thus  eliminated  in  twenty- 
four  hours  in  man  is  estimated  at  not  more  than  10  grammes. 
It  varies  greatly,  however,  with  temperature,  exercise,  etc. 

The  skin  is  highly  vascular  in  mammals,  and  its  importance 
as  a  heat  regulator  is  thus  very  great. 

When  an  animal  is  varnished  over,  its  temperature  rapidly 
falls,  though  heat  production  is  in  excess.  From  the  fact  that 
life  may  be  prolonged  by  diminishing  loss  of  heat  through 
wrapping  up  the  animal  in  cotton-wool,  it  is  inferred  that 
depression  of  the  temperature  is,  at  all  events,  one  of  the  causes 
of  death.  Though  the  subject  is  obscure,  it  is  likely  that  the 
retention  of  poisonous  products  so  acts  as  to  derange  metabo- 
lism, as  well  as  poison  directly,  which  might  thus  lead  to  the 
disorganization  of  the  machinery  of  life  to  the  point  of  disrup- 
tion or  death.  It  is  also  possible  that  the  reduction  of  the  tem- 
perature from  dilp.tation  of  the  cutaneous  vessels  may  be  so 
great  that  the  animal  is  cooled  below  that  point  at  which  the 
vital  functions  can  continue. 

The  Excretion  of  Perspiration. 

In  secretion  in  the  wider  sense  we  find  usually  certain  nerv- 
ous and  vascular  effects  associated.  The  vessels  supplying  the 
gland  are  dilated  during  the  most  active  phase,  and  at  the  same 
time  nervous  impulses  are  conveyed  to  the  secreting  cells  which 
stimulate  them  to  action.  There  is  a  certain  proportion  of 
water  given  off  by  transpiration ;  but  the  sweat,  as  a  whole, 
even  the  major  part  of  the  water,  is  a  genuine  secretion,  the 
result  of  the  metabolism  of  the  cells. 

Certain  experimental  facts  deserve  consideration  in  this  con- 
nection :  1.  If,  in  the  cat,  the  sciatic  nerve  be  divided  and  its 
distal  end  stimulated,  even  when  the  vessels  of  the  leg  are  liga- 
tured, the  corresponding  foot  sweats.  2.  The  vessels  being  un- 
touched and  atropin  injected  into  the  blood,  no  sweating  occurs 
on  stimulation  of  the  nerve,  though  the  vessels  of  the  foot 


PROTECTIVE   AND    EXCRETORY  FUNCTIONS  OP  THE  SKIN.  417 

dilate.  3.  If  a  kitten  with  divided  sciatic,  and  as  a  consequence 
dilated  blood-vessels  in  the  corresponding  limb,  be  placed  in  a 
warm  oven,  the  other  feet  will  sweat,  while  the  one  the  nerves 
going  to  which  have  been  divided  remains  dry.  4.  Perspira- 
tion will  take  place  in  a  cat  that  has  just  died  under  the  cir- 
cumstances mentioned  in  1.  From  these  experiments  it  is 
clear  that  nervous  influences  alone,  in  the  absence  of  any  vas- 
cular changes,  or  in  the  total  deprivation  of  blood,  suffice  to 
induce  the  secretion  of  perspiration. 

If  the  central  stump  of  the  divided  sciatic  be  stimulated, 
sweating  of  the  other  limbs  follows,  showing  that  perspiration 
may  be  a  reflex  act.  It  is  found  that  stimulation  of  the  periph- 
eral end  of  the  divided  cervical  sympathetic  leads  to  sweating 
on  the  corresponding  side  of  the  face. 

Hnman  Physiology. — Certain  nerves  (e.  g.,  the  cervical  sym- 
pathetic) have  been  stimulated  with  results  similar  to  those 
obtained  in  other  animals.  We  think  these  experiments  and 
certain  pathological  phenomena,  to  be  presently  mentioned,  of 
importance  beyond  their  immediate  application.  They  seem  to 
show  the  influence  of  nerves  over  vital  processes  in  the  clearest 
way,  and  render  it  probable  that  this  is  the  essential  element  in 
the  highest  vertebrates,  and  not  the  blood-supply,  which,  though 
important,  is  subsidiary.  The  path  of  the  sweat-nerves  is 
somewhat  similar  to  that  of  the  vaso-motor  fibers,  running 
mostly  in  the  sympathetic  in  some  part  of  their  course. 
Whether  there  is  a  dominant  center  in  the  medulla  and  subor- 
dinate ones  in  the  cord  is  a  matter  of  uncertainty  ;  though,  that 
the  cerebrum  can  exercise  a  powerful  influence  over  the  sudor- 
ific glands  is  evident  from  the  effect  of  emotions. 

Certain  drugs  seem  to  act  on  the  centers  through  the  blood ; 
others  on  either  the  nerve  terminals  or  the  gland-cells  them- 
selves. It  is  true  that  some  of  these  will  induce  sweating  after 
the  nerves  have  been  divided,  though  conclusions  as  to  the  nor- 
mal  action  of  a  part  from  such  experiments  must  be  drawn  with 
the  greatest  caution.  In  our  opinion  they  are  rather  suggest- 
ive than  demonstrative  in  themselves,  and  the  views  we  enter- 
tain of  normal  function  should  be  formed  from  a  consideration 
of  all  the  evidence  rather  than  that  from  a  single  experiment, 
however  striking  in  itself. 

Sweating  during  dyspnoea  and  from  fear,  when  the  cutane- 
ous surfaces  are  pale,  as  well  as  in  the  moribund,  shows  also 
the  independent  influence  over  the  sudorific;  glands  of  the  nerv- 
ous system.  Heat  induces  sweating  by  acting  both  reflexly  and 
27 


418  ANIMAL   PHYSIOLOGY. 

directly  on  the  sweat-centers  we  may  suppose.  Unilateral 
sweating  is  known  as  a  pathological  as  well  as  experimental 
phenomenon.  Perspiration  may  be  either  increased  or  dimin- 
ished in  paralyzed  limbs,  according  to  circumstances.  It  is 
possible  that  there  is  a  paralytic  secretion  of  sweat  as  of  saliva. 
The  subject  is  very  intricate  and  will  be  referred  to  again  on 
account  of  the  light  it  throws  on  metabolic  processes  generally. 

Absorption  by  the  skin  in  man  and  other  mammals  is,  under 
natural  conditions  probably  very  slight,  as  would  be  expected 
when  it  is  borne  in  mind  that  the  true  skin  is  covered  by  sev- 
eral layers  of  cells,  the  outer  of  which  are  hardened. 

Ointments  may  unquestionably  be  forced  in  by  rubbing; 
and  perhaps  absorption  may  take  place  when  an  animal's  tis- 
sues are  starving,  and  food  can  not  be  made  available  through 
the  usual  channels.  It  is  certain  that  abraded  surfaces  are  a 
source  of  danger,  from  affording  a  means  of  entrance  for  dis- 
ease-producing substances  or  for  germs. 

Comparative. — It  is  usually  stated  in  works  on  physiology 
that  the  horse  sweats  profusely,  the  ox  less  so ;  the  pig  in  the 
snout ;  and  the  dog,  cat,  rabbit,  rat,  and  mouse,  either  not  at  all 
or  in  the  feet  (between  the  toes)  only.  That  a  closer  observa- 
tion of  these  animals  will  convince  any  one  that  the  latter 
statements  are  incorrect,  we  have  no  doubt.  These  animals,  it 
is  true,  do  not  perspire  sensibly  to  any  great  extent;  but  to 
maintain  that  their  skin  has  no  excretory  function  is  an  error. 

Summary. — The  skin  of  the  mammal  has  protective,  sensory, 
respiratory,  and  excretory  functions.  The  respiratory  are  in- 
significant under  ordinary  circumstances  in  this  group,  though 
well  marked  in  reptiles  and  especially  in  batrachians  (frog, 
menobranchus).  Sweating  is  probably  dependent  on  the  action 
of  centers  situated  in  the  brain  and  spinal  cord,  through  nerves 
that  run  generally  in  sympathetic  tracts  during  some  part  of 
their  course.  While  the  function  of  sweating  may  go  on  inde- 
pendently of  abundant  blood-supply,  it  is  usually  associated 
with  increased  vascularity. 

Sweat  contains  a  very  small  quantity  of  solids,  is  alkaline 
in  reaction  when  pure,  but  liable  to  be  acid  from  the  admixture 
of  sebaceous  matter  that  has  undergone  decomposition.  Sebum 
consists  chiefly  of  olein,  palmitin,  soaps,  cholesterin,  and  ex- 
tractives of  little  known  composition.  The  salty  taste  of  the 
perspiration  is  due  chiefly  to  sodium  chloride,  and  its  smell  to 
volatile  fatty  acids ;  especially  is  this  so  of  the  sweat  of  certain 
parts  of  the  body  of  man  and  other  mammals. 


EXCRETION  BY  THE   KIDNEY. 


419 


The  functional  activity  of  the  skin  varies  with  the  tempera- 
ture, moisture,  etc.,  of  the  air  and  certain  internal  conditions ; 
especially  is  it  important  to  remember  that  it  is  one  of  a  series 
of  excretory  organs  which  act  in  harmony  to  eliminate  the 
waste  of  the  body,  so  that  when  one  functions  more  the  other 
may  and  usually  does  function  less. 

The  protective  function  of  the  skin  and  its  modified  epithe- 
lium (hair,  horns,  nails,  feathers,  etc.)  is  in  man  slight,  but  very 
important  in  many  other  vertebrates,  among  which  provision 
against  undue  loss  of  temperature  is  one  of  the  most  constant- 
ly operative,  and  enables  a  vast  number  of  groups  of  animals 
to  adapt  successfully  to  their  varying  surroundings. 


EXCRETION  BY  THE  KIDNEY. 

The  kidney  in  man  and  other  mammals  may  be  described  as 
a  very  complex  arrangement  of  tubes  lined  with  many  different 
forms  of  secreting  cells,  sur- 
rounded by  a  great  mesh- 
work  of  capillaries,  bound 
together  by  connective  tis- 
sue, the  quantity  varying 
with  the  animal,  and  the 
whole  inclosed  in  a  capsule. 
The  organ  is  well  supplied 
with  lymphatics  and  nerves. 
Though  the  tubes  are  so 
complex,  the  kidney  may  be 
divided  into  zones  which 
contain  mostly  but  one  kind 
f>f  tubule. 

Comparative. — Among  the 
lowest  forms,  the  Infusori- 
ans  and  CcpJenterates,  ex- 
cretory organs  have  not 
been  definitely  traced.  In 
tlie  Ferm^.s-,  organs  known 
as  nephridia  (segmental  or- 
gans, see  Figs.  253,  257)  are  ,  .     ^ 

°                  1    ,            /      ,             \      I-  Fio.  324.-Vertioal  section  of  kidney  (after  Sap- 

BUppOSed    to  act  the    part  OI  peyj.     l,  l,  a,  a,  3,  3,  a.  4,  4,  4,  4,  nyramids  of 

, ,        ,   .  ,             .                      /.      1  •  MalpiKhi  :   5,  5,  5,  5,  5,  f),  apicfs  of  pyramidH, 

the  kidney  m  some  lashlOn.  surrounded  by  calices  ;   (1,  (!,  coliiiimH  of  Ber- 

mv                     1                 i>i               Ml  tin  ;  7,  pelvis  of  kidney  ;  8,  upper  extremity  of 

lhe.se  are  long,  often  coiled         urvusr. 


420 


ANIMAL  PHYSIOLOGY. 


tubes  lined  with  cells,  and  with  an  internal,  cilated,  funnel- 
shaped  extremity  opening  into  the  body  cavity.     In  such  crus- 


FiG.  325.— structure  of  kidney  (after  Landois).  I.  Blood-vessels  and  tubes  (semi-diagi'am- 
matic).  A.  Capillaries  of  cortical  substance.  B.  Capillaries  of  medullary  substance. 
1,  artery  penetrating  Malpighian  body ;  2,  vein  enierging  from  a  Malpighian  body  ;  R- 
arteriolcB  rectse  ;  C,  ven»  rectte  ;  V,  V,  Interlobular  veins  ;  S,  stellate  veins  ;  I,  I,  cap. 
sules  of  Miiller  ;  X,  X,  convoluted  tubes  ;  T,  T,  T,  tubes  of  Henle  ;  N,  N,  N,  N,  communi- 
cating tubes ;  O,  O,  straight  tubes  ;  O,  opening  into  pelvis  of  kidney.  II.  Malpighian 
body.  A,  artery ;  jB,  vein  ;  C,  capillaries ;  K,  epithelium  of  capsule  ;  H,  beginning  of 
convoluted  tube.  III.  Rodded  cells  from  convoluted  tube.  1,  view  from  surface  ;  2,  side 
view  ((?,  granular  zone).  IV.  Cells  lining  tubes  of  Henle.  V.  Cells  lining  communicating 
tubes.    VI.  Section  of  straight  tube. 


EXCRETIOX  BY   THE  KIDNEY. 


421 


taceans  as  tlie  crayfish  the  green  gland  is  supposed  to  repre- 
sent a  kidney.  It  does  not  open  into  the  body  cavity  like  the 
preceding  and  the  following  form  of  the  organ.  It  is  well  sup- 
plied with  capillaries.     The  organ  of  Bojanus  (Fig.  30G)  is  the 


Fio.  326.— Blood-vessels  of  Malpighian  hoflies  and  convoluted  tubes  of  kidney  (after  Sappey). 
1,  1.  Malpit'hian  bodies  surround.-d  by  eajwiiles  ;  2,  2,  2,  convoluted  tubes  connected  with 
MaJpi^'inan  bodies  ;  :i.  arlcry  braiK-lilii^'  to  ko  to  Malj)iKhian  bodies  ;  4,  4,  4,  branches  of 
Z'X'^/  '  ^1  ^'  MaljiiKhian  bodies  from  which  a  portion  of  cai)sules  has  been  removed  ; 
<■  7,  (  vessels  passing  out  of  Malpighian  bodies  ;  «,  vessel,  branches  of  which  (9)  pass  to 
capillary  plexus  (10^ 

main  excretory  channel  in  many  groups  of  mollusks.  In  in- 
sects the  long,  coiled  Malj>ighian  tubules,  which  open  into  the 
intestine,  are  believed  to  secrete  both  bile  and  uric  .acid. 

Among  vertebrates,  till  the  reptiles  are  reached,  the  kidney 
is  a  persistent  Wolffian  body,  hence  its  more  sini])l('  form. 


422 


ANIMAL   PHYSIOLOGY. 


>C 


In  most  fishes  the  kidney  is 
a  very  elongated  organ,  though 
in  the  lowest  it  consists  of  little 
more  than  tubules,  coiling  but 
slightly,  ending  by  one  extrem- 
ity in  a  glomerulus  and  by  the 
other  opening  into  a  long  com- 
mon efferent  tube  or  duct.  The 
glomerulus  is,  however,  pecul- 
iar to  the  vertebrate  kidney. 
The  graded  complexity  in  ar- 
rangement, etc.,  of  the  tubes  is 
^-S  represented  well  in  the  figure 
below.  It  is  a  significant  fact 
that  the  kidney  of  the  human 
subject  is  lobulated  in  the  em- 
bryo, which  condition  is  persist- 
ent in  some  mammals  (rumi- 
nants, etc.). 

As  the  lungs  are  the  organs 
employed     especially    for    the 
elimination   of   carbonic  anhy- 
dride, so  the  kidneys  are  above 
all  others  the  excretors  of  the 
nitrogenous  waste  products  of 
the  body  chiefly  in  the  form  of 
uric  acid  or  urea.     Before  treat- 
ing of  secretion  by  the  kidney 
it  will  be  well  to  examine  into  the  physical  and  chemical  prop- 
erties of  urine  with  some  detail,  especially  on  account  of  its 
great  importance  in  the  diagnosis  of  disease. 


>P 


Fig.  327.— Diagrammatic  representation  of 
distribution  of  tubules  of  kidney  (after 
Huxley).  C.  cortical  region  ;  B,  bound- 
ary zone,  containing  large  part  of  Hen- 
le's  loops  :  P,  papillary  zone,  in  which 
are  the  main  outflow  tubules. 


Urine  considered  Physically  and  Chemically. 

Urine  is  naturally  a  fluid  of  very  variable  composition,  espe- 
cially regarded  quantitatively — a  fact  to  be  borne  in  mind  in 
considering  all  statements  of  the  constitution  of  this  fluid. 

Specific  Gravity. — Urine  must  needs  be  heavier  than  water,  on 
account  of  the  large  varietj''  of  solids  it  contains.  The  average 
specific  gravity  of  the  urine  for  the  twenty-four  hours  is  1015 
to  1030.  It.  is  lowest  in  the  morning  and  varies  greatly  with 
the  quantity  and  kind  of  food  eaten,  the  activity  of  the  lungs 
and  especially  of  the  skin,  with  emotions,  etc. 


EXCRETION   BY   THE  KIDNEY. 


423 


Color. — A  light  straw  color,  which  is  also  very  variable, 
being  increased  in  depth  either  by  the  presence  of  an  excess  of 
pigment  or  a  diminution  of  water.  There  are  probably  several 
pigments,  among  which  occur  urobilin,  derived  probably  from 
bile  pigment ;  urochrome,  becoming  red  on  oxidation ;  and 
indican,  wliich  may  be  oxidized  to  indigo. 

The  reaction  of  human  urine  is  acid,  owing  to  acid  salts,  espe- 
cially acid  sodium  phosphate  (NaH2P04).  There  is  usually  but 
a  trifling  quantity,  if  any,  of  free  acid  in  the  urine  when 
secreted.  The  acidity  diminishes  after  meals,  and  the  urine 
may  be  neutral  or  alkaline  when  the  food  is  wholly  vegetable, 
or  unduly  acid  when  the  diet  is  entirely  fleshy. 

ftuantity. — Usually  about  1,500  c.c.  or  from  50  to  52  ounces 
(two  pints)  in  twenty-four  hours.  This  is,  of  course,  like  the 
specific  gravity,  highly  variable,  and  frequently  they  run  par- 
allel with  each  other. 

The  following  tabular  statement  will  prove  useful  for  refer- 
ence : 


Quantitative  Estimation  of  the  Constituents  of  the  Urine  for 
Twenty-four  Hours  {after  Parkes). 


By  an  average 
man  of  65  kilos. 

Per  1  kilo  of 
body  weight. 

Water 

Total  solids 

Grammes. 

1500-000 

72-000 

33-180 

•555 

•400 

•910 

10-000 

2-012 

3-1(54 

7-000 

•770 

2-500 

11-090 

•200 

•207 

Grammes. 

23-000 
1-1000 

Urea ; 

Uric  acid 

-5000 
•0084 

Hippuric  aoid 

•0060 

Creatinin 

•0140 

Pigment,  etc 

Sulphuric  acid    

-1510 
-0305 

Phosphoric  acid 

Chlorine 

•0480 
•1260 

Ammonia 

Potassium 

Sodium 

Calcium .... 

Magnesium 

Attention  is  directed  more  particularly  to  the  preponderance 
among  the  solids  of  urea,  and  sodium  chloride,  for  the  latter  is 
the  form  in  whicli  a  large  part  of  tlu;  scxlium  reappears.  We 
may  say  that  in  round  numbers  about  35  grammes  or  500  grains 
{2  to  .">  per  cf'iit)  of  urea  are  excreted  daily. 

Nitrogenous  Crystalline  Bodies. — Tliese  are  the  derivatives  of 
the  metaljolistn  of  llie  bo<ly,  and  not  in  any  appreciable  degree 
drawn  from  the  food  itself.     Besides  urea,  and  of  much  less 


424  ANIMAL   PHYSIOLOGY. 

importance,  occurring  in  small  quantities,  are  bodies  that  may- 
be regarded  as  less  oxidized  forms  of  nitrogenous  metabolism, 
such  as  creatinin,  xanthin,  hypoxanthin  (sarkin),  hippuric  acid, 

ammonium  oxalurate,  and   urea,  CO  ]  -vrxr^     The   latter  was 

first  prepared  artificially  from  ammonium  cyanate,  tv^tt  |-  O, 
with  which  it  is  isoraeric. 

When  air  has  free  access  to  urine  for  some  time  in  a  warm 
room,  the  urea  becomes  ammonium  carbonate  by  hydration, 
probably  owing  to  the  influence  of  micro-organisms,  thus : 
CO  (^£[2)2  +  2  H2O  =  (NH4)2  CO3 ;  hence  the  strong  ammonical 
smell  of  old  urine,  urinals,  etc. 

Uric  acid  (C6H4N4O3)  occurs  sparingly  (see  table),  combined 
with  sodium  and  ammonium  chiefly  as  acid  salts.  Since  these 
salts  are  not  so  soluble  in  cold  as  in  warm  water,  they  often 
fall  as  a  sediment  in  the  vessel  in  which  the  urine  stands,  and 
present  a  brick-red  or  fawn  color. 

Uric  acid  is  itself  rather  insoluble  in  cold  water  or  hydro- 
chloric acid,  though  soluble  in  alkalies ;  hence  it  may  be 
obtained  by  adding  hydrochloric  acid  to  the  urine  in  the  cold. 
When  it  is  in  excess  it  may  separate  out  on  standing,  forming 
characteristic  colored  (dark-red)  crystals,  adhering  to  the  sides 
of  the  vessel,  floating  on  the  top  of  the  urine,  or  as  a  sediment 
at  the  bottom  (like  red-pepper  grains). 

Non-nitrogenous  Organic  Bodies. — Whether  traces  of  sugar  are 
normal  in  urine  is  as  yet  undetermined.  Certain  acids  occur, 
at  least  frequently,  in  small  quantities,  and  combined  mostly 
with  bases.  Among  these  are  lactic,  formic,  oxalic,  succinic, 
etc.  A  series  of  well-known  aromatic  bodies  occurs  in  urine, 
especially  in  that  of  the  horse,  cow,  etc.  These  are  phenol, 
cresol,  pyrocatechin,  which  occur  not  free,  but  united  with  sul- 
phuric acid. 

Inorganic  Salts. — These  are  mostly  in  simple  solution,  in  urine, 
and  not,  as  in  some  other  fluids  of  the  body,  united  with  pro- 
teid  bodies.  The  salts  are  chlorides,  phosphates,  sulphates, 
nitrates,  and  carbonates,  the  first  three  being  the  most  abun- 
dant ;  the  bases  being  sodium,  potassium,  calcium,  magnesium. 
Since  the  earthy  salts  can  not  remain  in  solution  in  an  alkaline 
fluid,  they  are  usually  found  as  a  sediment  when  the  urine  loses 
its  acid  reaction.  The  phosphates  are  to  be  traced  to  the  food, 
to  the  phosphorus  of  proteids,  and  to  phosphorized  fats  (leci- 
thin). The  sulphates  are  derived  from  those  of  the  food  and 
from  the  sulphur  of  the  proteids  of  the  body.     So  much  of  the 


EXCRETION  BY   THE  KIDNEY.  425 

carbonates  as  is  not  derived  directly  from  a  corresponding  sup- 
ply in  tlie  food  may  be  traced  to  tlie  oxidation  of  certain  or- 
ganic salts,  as  citrates,  tartrates,  etc. 

Doubtless  many  bodies  appear  either  regularly  or  occasion- 
ally in  urine  that  have  so  far  escaped  detection,  which  are,  like 
the  poisonous  exhalations  of  the  lungs,  not  the  less  important 
because  unknown  to  science. 

Abnormal  Urine. — There  is  not  a  substance  in  the  urine  that 
does  not  vary  under  disease,  while  the  possible  additions  act- 
ually known  are  legion.  These  may  be  derived  either  from 
the  blood  or  from  the  kidneys  and  other  parts  of  the  urinary 
tract.  The  kidneys  seem  to  take  upon  themselves  more  readily 
than  any  other  organ  the  duty  of  eliminating  foreign  matters 
from  the  body.  But  this  aspect  of  the  subject  is  too  wide  for 
detailed  consideration  in  this  work. 

The  student  of  medicine  should  be  thoroughly  familiar  with 
the  urine  in  its  normal  condition  before  he  enters  upon  the 
examination  of  the  variations  produced  by  disease.  This  is 
not  difficult,  and  much  of  it  may  be  carried  out  with  but  a 
meager  supjDly  of  apparatus.  For  this  purpose,  however,  we 
recommend  some  work  devoted  to  the  chemical  and  micro- 
scopic study  of  the  urine. 

It  greatly  assists  to  remember  a  few  points  in  regard  to 
solubilities.  From  a  physiological  point  of  view,  the  urine  and 
its  variations,  as  the  result  of  changes  in  the  organism,  may  be 
observed  with  advantage  in  one's  own  person — e.  g.,  the  influ- 
ence of  food  and  drink,  temperature,  emotions,  etc. 

Comparative. — The  urine  of  most  vertebrates  is  of  higher  spe- 
cific gravity  than  that  of  man.  In  fishes,  reptiles,  and  birds, 
uric  acid  replaces  urea,  and  is  very  abundant.  In  these  animals 
most  of  this  substance  is  white.  The  urine  is  passed  with  the 
feeces.  Among  mammals  the  urine  of  the  carnivora  is  strongly 
acid,  perhaps  owing  in  great  part  to  the  flesh  on  which  they 
feed ;  and  abounds  in  phosphates  and,  in  some  instances,  sul- 
phates. The  urine  is  so  concentrated  in  some  cases  that  we 
have  known  urea  nitrate  to  crystallize  out  on  the  addition  of 
nitric  acid  without  requiring  condensation. 

The  urine  of  the  herbivora  is  alkaline,  and  abounds  in  salts 
of  calcium,  especially  carbonates.  It  is  also  of  high  specific 
gravity,  and  grows  ra[)idly  dark  in  color  when  passed,  owing 
probably  to  the  presence  of  the  aromatic  compounds  referred 
to  above,  derived  from  the  food.  In  certain  groups  of  inverte- 
brates uric  acid  seems  to  be  a  normal  excretion. 


426  ANIMAL  PHYSIOLOGY. 


The  Secretion  of  Urine. 

Among  experimental  facts  from  which  important  conclu- 
sions have  been  drawn  are  the  following  (when  blood-pressure 
within  the  kidney  is  referred  to,  it  will  be  understood  that  the 
glomeruli  are  meant) :  1.  Section  of  the  spinal  cord,  which 
greatly  lowers  the  general  blood-pressure,  is  followed  by  dimi- 
nution or  total  arrest  of  the  secretion  of  urine.  2.  Section  of 
the  renal  nerves,  and  to  a  less  extent  of  the  splanchnics  de- 
creases the  flow  of  urine.  3.  Stimulation  of  the  spinal  cord 
after  section  of  the  above  nerves  (which  raises  the  blood-press- 
ure in  the  kidney  by  elevating  the  general  blood-pressure)  in- 
creases the  flow  of  urine.  4.  Certain  diuretics  increase  the 
blood-pressure,  either  generally  or  in  the  kidney,  while  others 
act  on  the  renal  epithelium,  apparently  independently  of  blood- 
pressure. 

By  means  of  apparatus  adapted  to  register  the  changes  of 
volume  the  kidney  undergoes,  it  is  found  that  the  kidney  not 
only  responds  to  every  general  change  in  blood-pressure,  but 


BLOOD     PRESSURE    CURVE 
KIDNEY    CURVE 

aAAAAAAAAAAAAAAAAA 


V vy vv  vv V vvvvv 


Fig.  338.— BP,  blood-pressure  curve  ;  K,  curve  of  the  volume  of  the  kidney ;  T,  time-curve, 
intervals  indicate  a  quarter  of  a  minute  ;  A,  abscissa  (Stirling,  after  Roy). 

to  each  heart-beat — that  is,  its  volume  varies  momentarily. 
This  shows  how  sensitive  it  is  to  variations  in  blood-pressure. 

From  the  above  and  other  experiments  it  has  been  concluded 
that  the  secretion  of  urine  is  largely  dependent  on  blood-press- 
ure. Until  very  recently  certain  experiments  (of  Nussbaum) 
were  considered  as  favoring  the  view  that  the  activity  of  the 
glomeruli  was  of  a  wholly  or  greatly  different  character  from 
that  of  the  tubules.  In  the  amphibia  (frog,  newt,  etc.)  there  is 
a  double  renal  blood-supply.  The  glomeruli  derive  their  blood 
from  the  renal  artery,  and  the  tubules  from  the  renal-portal 
system.  The  vein  returning  the  blood  from  the  lower  extrem- 
ity divides  (Fig.  231)  at  the  upper  part  of  the  thigh  into  two 
branches,  one  of  which,  entering  the  kidney,  breaks  up  into 


EXCRETION   BY   THE   KIDNEY.  427 

capillaries  around  the  tubules,  which  inosculate  to  some  extent 
with  the  vessels  emerging  from  the  glomeruli.  It  was  found 
that  when  certain  substances  were  injected  into  the  blood  they 
no  longer  appeared  in  the  urine  after  the  renal  artery  had  been 
tied,  from  which  it  was  concluded  that  they  were  secreted  only 
by  the  glomeruli,  and  that  the  blood  of  the  renal-portal  vein 
did  not  find  access  to  the  glomeruli.  This  conclusion  was  a 
pretty  bold  leap,  but  there  was  some  show  of  reason  for  it. 
More  recently,  however,  these  experiments  have  been  demon- 
strated to  be,  to  a  certain  extent,  unreliable,  and  that  the  pas- 
sage of  blood  from  the  venous  capillaries  backward  can  really 
take  place,  to  some  extent,  after  a  time. 

Theories  regarding  the  secretion  of  urine  may  be  divided 
into  those  that  are  almost  wholly  mechanical,  partly  mechani- 
cal, and  purely  secretory :  1.  To  the  first  class  belongs  that  of 
Ludwig,  which  teaches  that  very  dilute  urine  is  separated  from 
the  blood  in  the  glomeruli,  and  by  a  process  of  endosmosis  and 
absorption  of  water  by  the  tubular  capillaries  is  gradually 
concentrated  to  the  normal.  2.  As  an  example  of  the  second 
class  is  that  of  Bowman,  who  maintained  that  the  greater  part 
of  the  water  and  some  of  the  more  soluble  and  diffusible  salts  are 
separated  by  the  glomeruli  but  the  characteristic  constituents 
of  the  urine  by  the  epithelium  of  the  renal  tubules.  3.  As  an  ex- 
ample of  the  third  is  the  theory  of  Heidenhain,  who  attributed 
little  to  blood-pressure  in  itself,  and  much,  if  not  the  whole,  to 
the  secreting  activity  of  the  epithelium  of  the  tubules  more  par- 
ticularly. This  physiologist  showed  that  while  ligature  of  a 
vein  raised  the  blood-pressure  within  a  glomerulus,  it  was  not 
followed  by  any  increase  in  the  quantity  of  the  secretion,  but 
by  its  actual  arrest.  He  also  showed  that  injection  of  a  colored 
substance  (sodium  sulphindigodate)  into  the  blood,  after  the 
pressure  had  been  greatly  lowered  by  section  of  the  spinal 
cord,  led  to  its  appearance  in  the  urine ;  and  microscopic  exam- 
ination showed  that  it  had  passed  through  the  epithelial  cells 
of  the  tubules,  not  of  the  glomeruli. 

It  is  found,  however,  that  after  the  removal  of  a  ligature 
applied  to  the  i-enal  artery  the  urine  is  albuminous,  showing 
that  the  cells  have  been  plainly  injured  by  the  operation  ;  hence 
Heidenliain's  experiment  described  above  is  not  valid  against 
the  };lofKl-pressure  tlioory.  Moreover,  too  much  must  not  be 
inferred  frc^m  the  acticni  of  fc^reign  Hubstanc(;s  under  the  ab- 
normal conditions  of  such  an  experimcMit.  Wliilo  some  physi- 
ologists claim  that  tlie  glomeruli  are  lilt(iring  mechanisms,  tlioy 


428  .  ANIMAL  PHYSIOLOGY, 

explain  that  filtration  is  not  to  be  understood  in  its  ordinary 
laboratory  acceptation,  but  that  the  glomeruli  discriminate  as 
to  what  they  allow  to  pass,  yet  they  in  no  way  explain  how 
this  is  done.  They  make  the  whole  process  depend  on  blood- 
pressure,  and  attribute  little  special  action  to  the  flat  epithe- 
lium of  the  Malpighian  capsules. 

Though  we  can  not  admit  the  full  force  of  Heidenhain's  ex- 
periments as  he  interprets  them,  we  still  believe  that  his  views 
are  most  in  harmony  with  the  general  laws  of  biology  and  the 
special  facts  of  renal  secretion.  Recently,  after  a  repetition  of 
Nussbaum's  experiments,  and  the  institution-  of  others,  it  has 
been  rendered  clear  that  the  mechanical  theory  of  the  work  of 
the  kidney  can  not  hold,  even  of  the  glomeruli,  which  are 
shown  to  be,  as  we  should  have  expected,  true  secreting  organs. 
Now,  there  can  be  no  doubt  that  blood-pressure  is  a  most  im- 
portant determining  condition  here  as  in  other  secreting  pro- 
cesses, in  the  mammal  at  all  events  ;  but  whether  of  itself  or 
because  of  the  influence  it  has  on  the  rapidity  of  blood-flow,  it 
is  difficult  to  determine ;  or  rather  whether  solely  to  the  latter, 
for  that  the  constant  supply  of  fresh  blood  is  a  regular  con- 
dition of  normal  secretion  there  can  be  no  doubt.  Further,  it 
seems  probable  that  blood-pressure  has  more  to  do  with  the 
secretion  of  water  than  any  other  constituent  of  urine.  But 
we  maintain  that  it  should  be  called  a  genuine  secretion,  and 
that  nothing  is  gained  by  using  the  term  "filtration" — on  the 
contrary,  that  it  is  misleading,  and  tends  to  divert  attention 
from  the  real  though  often  hidden  nature  of  vital  processes. 
The  facts  of  disease  and  the  evidence  of  therapeutics,  we  think, 
all  favor  such  a  view  of  the  work  of  the  kidneys. 

Nerves  having  an  influence  over  the  secretion  of  urine  simi- 
lar to  those  acting  on  the  digestive  glands  have  not  yet  been 
determined.  The  powerful  influence  of  emotion,  especially  in 
those  of  unstable  nervous  system,  over  the  secretion  of  urine 
shows  that  there  must  be  nervous  channels  through  which  the 
nerve-centers  act  on  the  kidneys ;  though  whether  the  results 
are  not  wholly  dependent-  upon  vaso-motor  effects  may  be  con- 
sidered as  an  open  question  by  many.  We  think  such  a  view 
improbable  in  the  highest  degree.  The  most  recent  investiga- 
tions would  seem  to  show  that  the  vaso-motor  fibers  run  in  the 
dorsal  nerves,  especially  the  eleventh,  twelfth,  and  thirteenth, 
and  that  of  these  the  vaso-constrictors  are  the  best  developed. 

Pathological. — When  the  kidneys  are  excised,  the  ureters 
ligatured,  or  when  the  former  are  so  diseased  as  to  be  inca- 


EXCRETION   BY   THE   KIDNEY.  429 

pable  of  performing  their  functions,  death  is  the  result,  being 
preceded  by  marked  depression  of  the  brain-centers  passing 
into  coma.  Exactly  which  of  the  retained  products  brings 
about  these  results  is  not  known.  They  are  likely  due  to  sev- 
eral, and  it  impresses  on  the  mind  the  importance  of  those 
processes  by  which  the  constantly  accumulating  waste  is  elimi- 
nated. Uric  acid  when  not  removed  from  the  blood  and  tissues 
is  supposed  to  be  the  exciting  cause  of  gout.  An  excess  in  the 
form  of  urates  retained  or  deposited  in  certain  parts,  especially 
the  joints,  is  frequently  at  all  events  an  accompaniment  of  this 
disease. 

The  Expulsion  of  Urine. 

We  now  present  in  concise  form  certain  facts  on  which  to 
base  opinions  as  to  the  nature  of  the  processes  by  which  the 
bladder  is  emptied. 

It  will  be  borne  in  mind  that  the  secretion  of  urine  is  con- 
stant, though  of  course  very  variable;  that  the  urine  is  con- 
veyed in  minute  quantities  by  rhythmically  contractile  tubes 
(ureters)  which  open  into  the  bladder  obliquely ;  and  that  the 
bladder  itself  is  highly  muscular,  the  cells  being  arranged  both 
circularly  and  obliquely,  with  a  special  accumulation  of  the 
circular  fibers  around  the  neck  of  the  organ  to  form  the  sphinc- 
ter vesicce. 

1.  It  is  found  that  the  pressure  which  the  sphincter  of  the 
bladder  can  withstand  in  the  dead  is  much  less  (about  one 
third)  than  in  the  living  subject.  2.  We  are  conscious  of  being 
able  to  empty  the  bladder,  whether  it  contains  much  or  little 
fluid.  3.  We  are  equally  conscious  of  an  urgency  to  evacuation 
of  the  vesical  contents,  according  to  the  fullness  of  the  organ, 
the  quality  of  the  urine,  and  a  variety  of  other  conditions. 

4.  Emotions  may  either  retard  or  render  micturition  urgent. 

5.  In  a  dog,  in  which  the  cord  has  been  divided  in  the  dorsal 
region  some  months  previously,  micturition  may  be  induced 
reflexly,  as  by  sponging  the  anus.  0.  In  the  paralyzed  there 
may  be  retention  or  dribbling  of  urine.  7.  In  cases  of  urethral 
obstruction  from  a  calculus,  stricture,  etc.,  there  may  be  excess- 
ive activity  of  the  muscular  tissue  of  the  bladder-walls.  8. 
Evacuation  of  the  bladder  may  occur  in  the  absence  of  con- 
sciousness (sleep). 

The  most  obvious  conclusions  from  these  facts  are  that — 1. 
The  urine  finds  its  way  to  the  bladder  partly  through  muscular 
(peristaltic)  contractions  of  the  ureters,  partly  through  gravity, 


430  ANIMAL  PHYSIOLOGY. 

in  man  at  all  events,  and  partly  from  the  pressure  within  the 
tubules  of  the  kidneys  themselves.  2.  The  evacuation  of  urine 
may  take  place  independently  of  the  will  (see  8),  and  is  a  reflex 
(5)  act.  3.  Micturition  may  be  initiated  by  the  will,  which  is 
usually  the  case,  when  by  the  action  of  the  abdominal  muscles 
a  little  urine  is  squeezed  into  the  urethra,  upon  which  afferent 
impulses  set  up  contractions  of  the  bladder  by  acting  on  the 
detrusor  center  of  the  cord  and  at  the  same  time  inhibit  the 
center  presiding  over  the  sphincter  (if  such  there  be),  permit- 
ting of  its  relaxation.  4.  Emotions  seem  to  interfere  with  the 
ordinary  control  of  the  brain-centers  over  those  in  the  spinal 
cord.  5.  It  may  be  assumed  that  the  normal  tone  of  the 
sphincter  of  the  bladder  is  maintained  reflexly  by  the  spinal 
cord.  The  unwonted  muscular  contraction  associated  with  an 
obstruction  to  the  outflow  of  urine  may  be  in  part  of  nervous 
origin,  but  is  also,  in  all  probability,  owing  in  some  degree  to 
the  muscle-cells  resuming  an  independent  contractility,  due  to 
what  we  recognize  as  the  principle  of  reversion.  The  same  is 
seen  in  the  heart,  ureters,  and  similar  structures. 

Pathological. — There  may  be  incontinence  of  urine  from  pa- 
ralysis, the  cerebral  centers  being  unable  to  control  those  in 
the  spinal  cord.  Dribbling  of  urine  may  be  due  to  retention  in 
the  first  instance,  the  tone  of  the  sphincter  being  finally  over- 
come, owing  to  increase  of  pressure  within  the  bladder.  Over- 
distention  of  the  bladder  may  arise  in  consequence  of  lack  of 
tone  in  the  muscular  walls,  though  this  is  rare.  Strangury  is 
due  to  excessive  action  of  the  walls  of  the  bladder  and  the 
sphincter,  brought  about  reflexly,  when  the  organ  is  unduly 
irritable,  as  in  inflammation,  after  the  abuse  of  certain  drugs 
(cantharides),  etc. 

Comparative. — In  man  the  last  drops  of  urine  are  expelled  by 
the  action  of  the  bulbo-cavernosus  muscle  and  perhaps  some 
others.  In  the  dog  and  many  other  animals  the  regulated  and 
voluntary  use  of  this  muscle,  marked  in  a  high  degree,  produces 
that  interrupted  flow  so  characteristic  of  the  micturition  of 
these  animals. 

Summary. — Urine  is  in  man  a  fluid  of  specific  gravity  1015 
to  1020,  acid  in  reaction,  pale  yellow  in  color,  and  containing 
certain  salts,  pigments,  and  nitrogenous  bodies.  The  chief  of 
the  latter  is  urea,  which  is  excreted  daily  to  the  extent  of  about 
one  ounce  (500  grains). 

The  kidneys  and  skin  especially  supplement  one  another, 
and  normally  great  activity  of  the  one  implies  lessened  ac- 


THE   METABOLISM   OF  THE    BODY.  431 

tivity  of  the  other.  This  is  availed  of  in  the  treatment  of  dis- 
ease. 

Both  the  Malpighian  capsules  and  the  renal  tubules  have  a 
true  secretory  function,  though  the  larger  part  of  the  water  of 
urine  is  secreted  by  the  former.  Blood-pressure  is  an  important 
condition  of  secretion,  though  it  is  likely  that  this  is  so  chiefly 
because  it  favors  a  rapid  renewal  of  the  blood  circulating 
through  the  organ.  Whether  there  are  nerves  that  influence 
secretion  directly,  as  in  the  case  of  the  skin,  is  not  determined. 

Suppression  of  the  renal  functions  leads  to  symptoms  in 
which  the  nervous  system  is  recogni^ied  as  suffering  to  the 
extent  often  of  coma,  ending  in  death.  The  urine  of  most  other 
animals  is  more  concentrated  than  that  of  man ;  this  secretion 
in  carnivora  being  acid,  and  in  herbivora  alkaline  in  reaction 
when  passed  a  short  time. 

Our  information  in  regard  to  the  kidneys  has  been  derived 
experimentally  chiefly  from  the  study  of  the  frog  and  a  few  of 
the  domesticated  mammals,  especially  the  dog  ;  and  as  regards 
some  points  of  interest,  so  far  as  urine  is  concerned,  from  the 
bird  (guano),  and  the  horse,  ox  (aromatic  compounds),  etc. 
Man's  urine  has  been  thoroughly  studied ;  but  the  nature  of 
the  act  of  renal  secretion  is  in  his  case  a  matter  of  inference 
from  the  facts  of  pathology,  clinical  medicine,  therapeutics,  etc. 


THE  METABOLISM  OF  THE  BODY. 

In  the  widest  sense  the  term  metabolism  may  be  conven- 
iently applied  to  all  the  numerous  changes  of  a  chemical  kind, 
resulting  from  the  activity  of  the  protoplasm  of  any  tissue  or 
organ.  In  a  more  restricted  meaning  it  is  confined  to  changes 
undergone  by  the  food  from  the  time  it  enters  till  it  leaves  the 
body,  in  so  far  as  these  are  not  the  result  of  obvious  mechani- 
cal causes.  The  sense  in  which  it  is  employed  in  the  present 
chapter  will  be  plain  from  the  context,  though  usually  we  shall 
be  concerned  with  those  changes  effected  in  the  as  yet  compara- 
tively unjjropared  products  of  digestion,  by  which  they  are  ele- 
vated to  a  higher  rank  and  brought  some  steps  nearer  to  the 
final  goal  toward  which  they  have  been  tending  from  the  first. 
As  yet  our  attempts  to  trace  out  these  steps  have  been  little 
better  than  the  fruitless  efforts  of  a  lost  traveler  to  find  a  road, 
the  general  direction  of  which  he  knows,  but  the  ways  by  which 
it  is  reached  only  the  subject  of  plausible  conjecture.     But 


432  ANIMAL   PHYSIOLOGY. 

any  theories  that,  like  a  scaffolding,  allow  of  or  help  to  addi- 
tional investigation,  and  in  any  way  lead  out  into  a  clearer 
light,  are  not  without  value;  and  on  this  principle  we  shall 
treat  the  subject,  spending  but  little  time  in  barren  fields 
except  as  they  have  an  interest  from  the  suggestiveness  of  the 
results,  even  though  negative. 

The  Metabolism  of  the  Liver, 

This  organ  has  two  well-recognized  functions :  1,  The  for- 
mation of  bile.     2,  The  formation  of  glycogen. 

We  have  already  considered  the  first,  and  ascertained  how 
little  is  positively  known.     Let  us  now  examine  the  second. 

Glycogen  may  be  obtained  from  the  liver  of  mammals,  such 
as  the  rabbit,  by  rapidly  killing  the  animal,  excising  the  warm 
still  living  organ,  cutting  into  fine  pieces,  throwing  them  into 
boiling  water,  removing  after  a  few  minutes  and  grinding  in  a 
mortar  and  reimmersing  in  the  boiling  water  ;  on  now  passing 
the  latter  through  a  coarse  filter  a  turbid,  whitish  fluid  is  ob- 
tained containing  the  extracted  glycogen  as  proved  by  giving 
a  red  color  with  solution  of  iodine.  The  substance  may  be  ob- 
tained as  a  whitish  amorphous  powder,  having  the  chemical  com- 
position of  starch,  and  has  in  fact  been  termed  animal  starch. 

By  appropriate  treatment  it  may  be  converted  into  sugar  by 
a  process  of  hydration  (CeHioOs  +  H2O  =  CeHjsOe). 

If,  after  the  death  of  an  animal,  the  liver  be  kept  at  body 
temperature  for,  say,  an  hour,  very  little  glycogen  can  be  recov- 
ered from  it,  but  instead  abundance  of  sugar.  These  facts  sug- 
gest that  the  sugar  present  represents  the  original  glycogen, 
and  that  the  conversion  has  been  effected  by  some  ferment, 
which  does  not  act  during  life,  though  why  not  is  one  of  the 
problems  ranking  with  the  non-digestion  of  the  stomach  by  its 
own  ferments,  etc. 

We  have  already  expressed  our  doubts  as  to  the  justifia- 
bility of  resorting  to  so  many  "  ferments  "  to  explain  the  facts 
of  physiology,  and  in  the  present  case  there  is  another  possible 
view  of  the  matter.  It  is  conceivable  that  the  conversion, 
under  these  circumstances,  of  the  glycogen  into  sugar,  may  be 
an  act  of  the  dying  protoplasm  of  the  liver-cells ;  and  there  are 
experimental  results  which  tend  to  strengthen  such  a  view. 

The  principal  facts  as  to  the  storage  of  glycogen  in  the  liver 
may  be  briefly  stated  thus  : 

1.  Glycogen  has  been  found  in  the  liver  of  a  large  number 


THE  METABOLISM   OF  THE   BODY.  433 

of  groups  of  animals  including  some  invertebrates.  2.  Among 
mammals  it  is  most  abundant  when  the  animal  feeds  largely 
on  carbohydrates.  3.  It  is  found  in  the  liver  of  the  carnivora, 
and  in  those  of  omnivora,  when  feeding  exclusively  on  flesh. 
4.  When  an  animal  starves  (does  not  feed),  the  glycogen  grad- 
ually disappears.  5.  A  fat-diet  does  not  give  rise  to  glycogen. 
G.  During  early  foetal  life  glycogen  is  found  in  all  the  tissues, 
but  later  it  is  restricted  more  and  more  to  the  liver,  though 
even  in  adults  it  is  to  be  found  in  various  tissues,  especially  the 
muscles,  from  which  it  is  almost  never  absent. 

From  the  facts  the  inference  is  plain  that  glycogen  is  formed 
from  carbohydrate  materials ;  or,  to  be  rather  more  cautious, 
that  the  formation  of  this  substance  is  dependent  on  the  pres- 
ence of  such  material  in  the  food.  Inasmuch  as  glycogen  oc- 
curs in  muscle,  it  does  not  follow,  from  the  fact  of  its  presence 
in  the  liver  of  carnivorous  animals,  that  it  is  manufactured 
from  proteid  substances,  though  this  is  not  more  difficult  to 
understand  chemically  than  the  formation  of  fat  from  this 
source  which  is  well  established. 

Starch,  it  is  well  known,  occurs  abundantly  in  plants,  and 
there  is  no  doubt  that  the  sugar  often  present  in  abundance  has 
starch  as  its  antecedent,  and  vice  versa.  Analogy,  then,  points 
to  such  a  relation  between  carbohydrate  food  and  glycogen  for- 
mation on  the  one  hand,  and  reconversion  of  glycogen  into 
sugar  on  the  other.  And  recent  investigations  tend  to  show 
that  plant  metabolism  bears  a  greater  resemblance  to  that  of 
animals  than  was  till  recently  supposed,  thus  giving  greater 
force  to  the  argument  from  analogy,  though  this  is  recognized 
as  generally  a  dangerous  one. 

Assuming  this  relation  between  food-stuffs  and  glycogen  to 
hold,  the  question  arises.  How  is  the  substance  formed  by  the 
liver?  There  are  three  conceivable  methods :  1.  The  liver-cells 
may,  we  know  not  how,  simply  dehydrate  the  sugar  of  diges- 
tion as  carried  to  them  in  the  portal  blood.  2,  The  cells  may 
manufacture  glycogen  from  their  own  protoplasm,  in  which 
process  the  portal  sugar  is  in  some  way  used.  3.  The  liver-cells 
may  always  be  engaged  in  the  construction  of  glycogen  as  the 
gastric  cells  of  pejjsinogen,  but  the  accumulation  or  removal  of 
tlie  substance  depends  on  the  character  of  the  food  especially; 
thus,  if  the  latter  abounds  in  carbohydrates,  the  blood  will  be 
well  supplifid  with  sugar,  so  that  the  glycogen  need  not  undergo 
its  usual  conversion  into  that  suV>stance.  None  of  these  views 
has  been  definitely  proved  to  be  the  correct  one. 

28 


434 


ANIMAL   PHYSIOLOGY, 


The  Uses  of  Glycogen. — Whetlier  tlie  blood  of  the  hepatic  vein 
contains  more  sugar  than  that  of  the  portal  vein  has  long  been 
a  subject  of  controversy.  If  the  affirmative  could  be  established, 
it  would  be  pretty  clear  that  glycogen  stored  in  the  liver-cells 
was  transformed  into  sugar,  possibly  by  a  process  of  hydration. 
But,  considering  the  rapidity  of  the  blood-stream,  it  is  easy  to 
understand  that  a  large  amount  of  sugar  might  be  conveyed 


Main  venous  trunk 


Bight  auricle 


Vena  cava 


Hepatic  vein- 


Lymph,  gland 


Portal  system 


"^Ollnti  ^yrnvhatic 


Blood  vessel,  tissue  cells, 
0r)'^S>ff  lymph-spaces 


Alimentary  tract 


Fig.  329.— Diagram  intended  to  illustrate  the  general  relations  of  blood  and  lymph  to  metab- 
oUsm  (nutrition) ;  and  the  method  by  which  the  portal,  lymphatic,  and  general  venous 
systems  are  related  to  the  alimentary  tract. 


into  the  general  circulation,  and  yet  the  blood,  whether  of  the 
hepatic  vein  or  of  other  parts,  contain  but  a  small  quantity  at 
any  one  time.  The  blood  is  kept  of  a  certain  fairly  constant 
composition,  both  by  the  action  of  the  excreting  organs  and  by 
the  withdrawal  from  it  of  supplies  for  the  tissues.  Moreover, 
that  correlation  of  functional  work  on  which  we  have  already 
insisted,  is  not  to  be  forgotten.  One  must  not  conceive  of  the 
liver-cells  or  any  others  doing  their  work  independently  of  the 
condition  of  their  fellow  cell-units  in  the  organic  common- 
wealth. We  mean  to  say  that  the  amount  of  glycogen  trans- 
formed to  sugar  will  depend  on  a  great  many  circumstances 
outside  of  the  liver  itself.  Such  aspects  of  the  case  have  been 
rather  overlooked.  According  to  another  theory,  glycogen  is 
an  intermediate  product  between  sugar  and  fat,  but  of  this 
there  is  very  little  evidence  indeed ;  and,  besides,  fat  formation 
is  otherwise  well  enough  accounted  for,  though,  of  course,  too 
much  stress  must  not  be  laid  upon  such  an  argument. 

What  is  the  fate  of  the  transformed  glycogen  ?    What  be- 
comes of  the  sugar  ?    We  can  answer,  negatively,  that  it  is  not 


THE   METABOLISM   OF  THE   BODY.  435 

used  up  in  the  blood,  it  is  not  oxidized  there;  but  by  what 
tissues  it  is  used  or  how  it  is  made  available  in  the  economy  is 
a  subject  on  which  we  are  profoundly  ignorant.  The  presence 
of  so  much  glycogen  in  the  partially  developed  tissues  of  the 
foetus  points  to  its  importance,  and  suggests  its  being  a  crude 
material  which  is  laid  up  to  be  further  elaborated,  as  in  vege- 
tables, by  the  growing  protoplasm. 

Glycogen  being  so  generally  present  in  muscle,  its  diminu- 
tion running  parallel,  to  some  extent  at  least,  with  the  func- 
tional activity  of  the  tissue,  it  is  clear  that  there  is  some  im- 
portant purpose  served ;  but  here  again  we  inquire,  What  ? 

Pathological. — If  a  point  in  the  medulla  oblongata  of  a  rabbit, 
corresponding  nearly  or  comjiletely  with  the  vaso-motor  center, 
be  punctured,  the  urine  will  in  a  few  hours  be  found  aug- 
mented in  quantity  and  containing  sugar. 

It  is  further  found  that  the  quantity  of  the  latter  bears 
some  relation  to  the  diet  of  the  animal,  one  well  fed  on  carbo- 
hydrates having  more  sugar  in  the  urine  than  a  fasting  animal. 
From  these  facts  it  has  been  concluded  that  the  nervous  system 
has  lost  a  customary  normal  influence  over  the  glycogenic 
function,  either  directly  through  the  action  of  the  nerves  on 
the  liver-cells  or  through  the  loss  of  tone  arising  from  injury 
to  the  vaso-motor  center.  Poisoning  by  carbonic  oxide  and  the 
administration  of  certain  drugs  also  causes  sugar  to  appear  in 
the  urine. 

The  symptoms  resulting  from  puncture  of  the  medulla,  etc., 
have  been  spoken  of  as  "  artificial  diabetes  " — a  very  objection- 
able term  for  which  artificial  glycosuria  should  be  substituted. 
There  is  a  grave  and  often  fatal  disease  known  as  diabetes 
mellitus,  one  of  the  symptoms  of  which  is  the  apjjearance  often 
of  enormous  quantities  of  grape-sugar  in  the  urine.  But  all 
attempts  to  fathom  the  dej)ths  of  obscurity  which  surround  this 
malady  have  been  in  vain.  It  would  seem  that  attention  has 
been  directed  too  exclusively  to  the  liver.  Cases  of  the  disease 
occur  in  which  at  the  2^ost-mortein  examination  the  liver  may 
be  perfectly  normal  in  appearance,  or  either  hypersemic  or 
ansemic. 

It  seems  to  us  that  it  is  likely  that  the  disease  will  be  shown 
to  be  of  diverse  origins,  or  certainly  not  referable  to  one  organ 
solely  in  most  cases.  The  conclusion  that  the  nervous  system 
is  greatly  concerned,  both  in  directing  the  glycogenic  functions 
of  the  liver  and  in  the  disease  in  question,  seems  to  be  un- 
doubted ;  vaso-motor  effects,  when  present,  being  probably  of 


436 


ANIMAL  PHYSIOLOGY. 


secondary  importance.  We  donbt,  however,  if  the  results  of 
the  above-mentioned  experiment  warrants  any  inferences  as  to 
the  normal  glycogenic  functions. 

The  instructive  part  about  the  disease  diabetes  is  the  man- 
ner in  which  the  course  of  events  emphasize  the  importance 
of  co-ordination  among  the  vital  processes,  and  the  constant 
necessity  for  regulation  of  them  all  by  the  nervous  system. 
Diabetes  seems  to  imply  that  these  processes  have  escaped  this 
normal  control  and  are  running  riot. 

Metabolism  of  the  Spleen. 


The  physiological  significance  of  the  peculiar  structure  of 
this  organ,  though  not  yet  fully  understood,  is  much  plainer 


Fis.  330. — Vertical  section  of  a  small  superficial  portion  of  human  spleen,  seen  with  low  power 
(Schafer).  A,  peritoneal  and  fibrous  covering  ;  b,  trabeculee  ;  c,  c,  Malpighian  corpuscles, 
in  one  of  which  an  artery  is  seen  cut  transversely,  in  the  other,  longitudinally  ;  d,  injected 
arterial  twigs  ;  e,  spleen-pulp. 

than  it  was  till  recently.  The  student  is  recommended  to  look 
carefully  into  the  histology  of  the  spleen,  especially  the  dis- 
tribution of  its  muscular  tissue  and  the  peculiarities  of  its 
blood-vascular  system.  It  has  already  been  pointed  out  that 
there  is  little  doubt  that  leucocytes  are  manufactured  here  even 
in  the  adult,  possibly  also  red  cells ;  and  that  the  latter  are  dis- 
integrated, and  the  resulting  substances  worked  over,  possibly 
by  this  organ  itself.  This  view  is  rendered  probable,  not  only 
by  microscopic  study  of  the  organ,  but  by  a  chemical  examina- 


THE  METABOLISM   OP  THE   BODY. 


43T 


tion  of  the  splenic  pulp ;  for  a  ferruginous  proteid,  and  numer- 
ous pigments,  of  a  character  such  as  harmonizes  with  this  con- 
ception, are  found. 

The  fact  that  the  spleen-pulp  does  not  agree  in  composition 
with  either  blood  or  serum ;  that  it  abounds  in  extractives  such 


Fig.  331.— Thin  section  of  spleen-pulp,  highly  magnified,  showing  mode  of  origin  of  a  small 
vein  in  the  interstices  of  pulp  (Sohafer).  i\  vein  filled  with  blood-corpuscles,  which  are  in 
continuity  with  others.  6/,  filling  up  interstices  of  retiform  tissue  of  pulp  ;  iv,  wall  of 
vein.    The  shaded  bodies  among  red  corpuscles  are  pale  corpuscles. 

as  lactic,  butyric,  formic,  and  acetic  acids,  together  with  inosit, 
xanthin,  hypoxanthin,  leucin  and  uric  acid — points  to  its  being 


Fio.  332.— Portion  of  splet-n  of  cat,  sh  )wing  Malpighian  (lymphatic)  corpuscle  (after  Cadiat). 
A,  arli'ry  aroimd  which  cori>UHcle  Ls  placed  ;  B,  meshes  of  spleen-pulp,  injected  ;  C.  artery 
of  c<)r[nis<;l<'  ramifying  in  lymphatic  tissue.  The  clear  space  around  corpuscle  represents 
a  lymphatic  sinus. 

the  seat  of  a  complex  metaboli.sm,  though  neither  the  changes 
themselves  nor  their  ])Ui-pose  arc;  well  understood. 

Nevertheless,  it  must  be  admitted  tiiat  to  recognize  this  was 
a  great  advance  upon  tlic;  view  that  tiu;  spleen  luid   no  inijjor- 


438  ANIMAL  PHYSIOLOGY. 

taut  function,  and  that  this  was  shown  by  the  removal  of  the 
organ  without  change  in  the  animal's  economy. 

But  to  believe  that  there  are  no  such  changes,  and  to  have 
clear  proof  of  it,  are  two  different  things.  As  a  matter  of  fact, 
closer  study  does  show  that  in  some  animals  there  are  altera- 
tions in  the  lymphatic  glands  and  bone-marrow,  which  organs 
are  undoubtedly  manufacturers  of  blood-cells. 

These  changes  are  unquestionably  compensatory,  and  that 
other  similar  ones  corresponding  to  comparatively  unknown 
functions  of  the  spleen  have  not  as  yet  been  discovered  is  owing 
likely  to  our  failures  rather  than  their  real  absence.  We  dwell 
for  a  moment  on  this,  because  it  illustrates  the  danger  of  the 
sort  of  reasoning  that  has  been  applied  in  the  case  of  this  and 
other  organs ;  and  it  shows  the  importance  of  recognizing  the 
force  of  the  general  principles  of  biology,  and  also  the  desira- 
bility of  refraining  from  drawing  conclusions  that  are  too  wide 
for  the  premises.  In  every  department  of  physiology  it  must 
be  more  and  more  recognized  that  what  is  true  of  one  group 
of  animals  is  not  necessarily  true  of  another,  or  even  of  other 
individuals,  though  the  differences  in  the  latter  case  are  of 
course  usually  less  marked.  "We  have  referred  to  this  be- 
fore, and  shall  do  so  again,  for  it  is  as  yet  but  too  little  con- 
sidered. 

Examinations  of  the  spleen,  carried  out  by  means  of  the  on- 
cograph, as  in  the  case  of  the  kidney,  reveal  the  following  facts: 
1.  The  spleen  undergoes  slight  changes  in  volume,  correspond- 
ing to  the  respiratory  undulations  of  blood-pressure,  but  not,  as 
■with  the  kidney,  to  each  heart-beat.  2.  The  spleen  experiences 
rhythmic  variations  in  size,  independent  of  the  general  blood- 
pressure.  It  will  be  borne  in  mind  that  the  splenic  arteries  end 
in  capillaries,  but  that  some  of  the  arterial  blood  finds  its  way 
possibly  from  the  capillaries  into  the  splenic  pulp,  from  which 
it  is  taken  up  by  veins  beginning  in  this  tissue. 

It  is  highly  probable,  then,  that  these  movements  serve  to 
proi^el  the  blood  that  has  found  its  way  into  the  pulp-tissue  on- 
ward into  the  veins  ;  and  it  is  not  to  be  forgotten  that  among 
large  groups  of  invertebrates,  in  which  capillaries  are  wanting, 
a  not  very  unlike  method  of  carrying  on  the  general  circula- 
tion is  found ;  at  the  same  time,  we  may  suppose  that  such  an 
arrangement  of  blood-supply  and  removal  would  not  be  un- 
favorable to  splenic  metabolism. 

There  is  one  fact  in  the  metabolism  of  the  spleen  that  de- 
serves special  notice,  though  we  can  not  indicate  all  its  bear- 


THE   METABOLISM   OF   THE   BODY.  439 

ings.    Uric  acid  is  found  in  the  spleen,  even  of  herbivorous 
aniraals,  though  not  in  their  urine. 


Abscigaa  of  Blood- pressure  curve.  3  seconds  intervals. 

MIIIUMMIIIIIUIIIIIIIIIUIIIIIIIilUIIIIIIIIIUIMIIIIIIUIMIIMI   I  LTTT- 

FiG.  333.— Tracing  of  splenic  variations  in  size,  taken  -with  the  oncograph  (after  Roy).  The 
increase  in  volume  is  indicated  in  upper  curve  by  the  ascent  and  the  diminution  by  the 
descent.  The  tracing  below  is  of  the  blood -pressure  as  taken  in  carotid  artery  of  dog. 
The  lower  line  indicates  time  markings 

It  is  known  that  this  constituent  of  the  urine  is  increased  in 
intermittent  fever  (ague),  in  which  disease  the  spleen  is  often 
greatly  enlarged.  The  vascular  engorgement  and  the  height- 
ened metabolism  of  the  spleen  seem  to  be  associated ;  and  the 
fact  that  the  uric-acid  diathesis  is  often  intensified  if  not  origi- 
nated by  overfeeding,  suggests  a  connection  between  the  spleen 
and  the  digestive  system  at  all  events.  Much  as  there  is  that 
remains  obscure,  we  think  it  can  not  be  doubted,  on  the  evi- 
dence furnished,  that  the  spleen  must  serve  some  very  impor- 
tant purpose  in  the  economy,  apart  from  its  relations  to  the 
blood,  noticed  in  an  earlier  chapter. 

The  dominion  of  the  nervous  system  over  the  spleen  is  evi- 
dent from  various  facts.  The  spleen  may  be  diminished  in  size 
either  generally  by  the  stimulation  of  the  vagus  or  splanchnic 
nerves  directly,  or  reflexly  through  stimulation  of  one  of  the 
afferent  nerves ;  and,  locally,  by  direct  application  of  the  elec- 
trodes to  the  surface  of  the  organ.  Stimulation  of  the  medulla 
itself  also  leads  to  contraction  of  the  organ.  It  would  seem 
that  not  only  the  arteries  but  the  organ  as  a  whole  is  main- 
tained in  a  state  of  tonic  contraction  to  a  certain  extent  by  the 
agency  of  the  nervous  system.  Not  only  so,  but,  if  we  may 
judge  from  the  analogy  of  other  organs,  wo  may  bf^lieve  that 
its  metabolism  is  directly  controlled  by  the  nervous  system. 


440  ANIMAL   PHYSIOLOGY. 


The  Consteuction  of  Fat. 

It  is  a  well-known  fact  that,  speaking  generally,  a  diet  ricli 
in  carbohydrates  favors  fat  formation,  both  in  man  and  other 
animals ;  though  it  is  not  to  be  forgotten  that  many  persons 
seem  to  be  unable  to  digest  such  food,  or,  at  all  events,  to  as- 
similate it  so  as  to  form  fat  to  any  great  extent.  Persons  given 
to  excessive  fat  production  are  as  frequently  as  not  sparing 
users  of  fat  itself. 

It  is  possible  in  man  and  probable  in  ruminants  that  fer- 
mentations may  occur  in  the  intestines  giving  rise  to  fatty  acids 
which  are  possibly  converted  into  fats  by  the  cells  of  the  villi 
or  elsewhere.  Certain  feeding  experiments  favor  the  view  that 
carbohydrates  may  be  converted  into  fat  or  in  some  way  give 
rise  to  an  increase  in  this  substance ;  for  it  is  to  be  borne  in 
mind  that  fat  may  arise  from  a  certain  diet  in  various  ways 
other  than  its  direct  transformation  into  this  substance  itself. 

There  are  certain  facts  that  make  it  clear  that  fat  can  be 
formed  from  proteids :  1.  A  cow  will  produce  more  butter  than 
can  be  accounted  for  by  the  fat  in  her  food  alone.  2.  A  bitch 
which  had  been  fed  on  meat  produced  more  fat  in  her  milk 
than  could  have  been  derived  directly  from  her  food,  and  this, 
when  the  animal  was  gaining  in  weight,  which  is  usually  to 
be  traced  to  the  addition  of  fat ;  so  that  the  fat  of  the  milk 
was  not,  in  all  probability,  derived  from  that  of  the  dog's 
body;  and,  as  will  be  seen  presently,  can  be  accounted  for 
without  such  a  supposition.  3.  It  has  been  shown  by  analysis 
that  472  parts  of  fat  were  deposited  in  the  body  of  a  pig  for 
every  100  in  its  food. 

These  facts  of  themselves  suffice  to  show  that  fat  can  be 
formed  from  proteid,  or  at  least  that  proteid  food  can  of  itself 
give  rise  to  a  metabolism,  resulting  in  fat  formation ;  and  the 
latter  is  probably  the  better  way  to  state  the  case  in  the  present 
condition  of  knowledge. 

An  examination  of  the  percentage  composition  of  proteid 
and  urea  renders  a  possible  construction  of  fat  from  proteid 
conceivable  and  in  harmony  with  other  better  known  physi- 
ological facts. 

Carbon.       Hydrogen.      Nitrogen.         Oxygen.      Sulphur. 

Proteid 53-00  7-30  15-53  23-04  1-13 

Urea 20-00  6-66  46-67  26-67 

It  will  be  seen  that,  if  we  assume  that  the  urea  discharged 
represents  the  whole  of  the  nitrogen  that  passes  through  the 


THE   METABOLISM   OF   THE   BODY. 


441 


body,  there  would  remain  for  disposal  otherwise  a  large  amount 
of  carbon,  for  there  is  nearly  three  times  as  much  of  this  ele- 
ment in  proteid  as  in  urea ;  so  that  it  is  possible,  from  a  chemi- 
cal point  of  view,  to  understand  the  origin  of  fat  from  the  pro- 
teid food ;  but  too  much  importance  must  not  be  attached  to 
such  speculations. 

That  fat  is  a  real  formation,  dependent  for  its  composition 
on  the  work  of  living  tissues,  is  clear  from  the  well-known  fact 
that  the  fat  of  one  animal  differs  from  that  of  another,  and  that 
it  preserves  its  identity,  no  matter  what  the  food  may  be,  or  in 
what  form  fat  itself  may  be  provided.  Certain  constituents  of 
the  animal's  fat  may  be  wholly  absent  from  the  fat  of  its  food, 
yet  they  appear  just  the  same  in  the  fat  produced  under  such 
diet.  Even  bees  can  construct  their  wax  from  proteid,  or  use 
unlike  substances,  as  sealing-wax. 

But  histological  examination  of  forming  adipose  tissue  itself 
throws  much  light  upon  the  subject.  Fat-cells  are  those  in 
which  the  protoplasm  has  been  largely  replaced  by  fat.  The 
latter  is  seen  to  arise  in  the  former  as  very  small  globules 


Fio.  334. -Mammary  Kland  of  iiiiman  female  (after  LiC-Keois*.  1,  sinus,  or  dilatatlrm  of  one  of 
lactiferous  ducts  ;  2,  extremities  of  the  ducts  ;  3,  lobules  of  gland  ;  4,  nipple,  retracted  In 
center ;  5.  areola. 


442 


ANIMAL   PHYSIOLOGY. 


wMch.  run  together  more  and  more  till  they  may  wholly  re- 
place the  original  protoplasm. 

The  history  of  the  mammary  gland  is,  perhaps,  still  more 
instructive.  In  this  case,  the  appearance  of  the  cells  during 
lactation  and  at  other  periods  is  entirely  different.     Fat  may 


Fig.  335.— Section  of  mammary  gland  (udder  and  nipple)  of  cow  (after  Thanhoffer).  Ma,  sub- 
stance of  gland  ;  N,  nipple  ;  A,  acini  of  gland  ;  m.  d,  milk-ducts  ;  C,  milk-cisterns  ;  /. 
folds  in  wide  milk-ducts  ;  aS,  section  of  sphincter  muscle  ;  s,  external  skin ;  n.  in.  d,  narrow 
milk-duct  in  nipple. 

be  seen  to  arise  within  these  cells  and  be  extruded,  perhaps  in 
the  same  way  as  an  Amoeba  gets  rid  of  the  waste  of  its  food. 
So  far  as  the  animal  is  concerned,  milk  is  an  excretion  in  a 
limited  sense. 


THE   METABOLISM   OP   THE   BODY. 


443 


It  is,  in  the  nature  of  the  case,  impossible  to  follow  with 
the  eye  the  formation  and  separation  of  milk-sugar,  casein,  etc. 


Fig.  33t.— I.  Acinus  from  mamma  of  a  bitch  when  inactive  (after  Heidenhain).    H.  During 
secretion  of  milk,    o,  6,  milk-globules  ;  c,  d,  e,  colostrum-corpuscles  ;  /,  pale  cells. 

But  the  whole  process  is  plainly  the  work  of  the  cells,  and  in 
no  mechanical  sense  a  mere  deposition  of  fat,  etc,  from  the 
blood ;  and  the  same  view  applies  to  the  construction  of  fat  by 
connective  (adipose)  tissue. 


Vo   °    o  O  oo  o.P  tsSS%V  'Coo   °o°o°  oOq  „o< 

Fio.  337. 

Fio.  3.37.— Human  milk-globules,  from  a  healthy  lying- 

(Funke). 
Fio.  :5JX.— Colostrum,  from  a  healthy  lying-in  woman, 

The  colostrum-corpuscles  are  large  and  granular  ; 

secretion. 


Fig.  338. 
in  woman,  eight  days  after  delivery 

twelve  hours  after  delivery  (Funke). 
they  gradually  disappear  from  the 


Whether  fat,  as  such,  or  fatty  acid,  is  dealt  with  without 
being  built  up  into  the  protoplasm  of  the  cell,  is  not  known  ; 
but,  taking  all  the  facts  into  the  account,  and  considering  the 
behavior  of  cells  generally,  it  seems  most  natural  to  regard 
the  construction  of  fat  as  a  sort  of  secretion  or  excretion.  To 
suppose  that  a  living  cell  acts  upon  material  in  the  blood  as  a 
workman  in  a  factory  on  his  raw  material,  or  even  as  a  chemist 


444 


ANIMAL  PHYSIOLOGY. 


does  in  the  laboratory,  seems  to  be  too  crude  a  conception  of 
vital  processes.     Until  it  can  be  rendered  very  mucli  clearer 


Fig.  339.— Microscopic  appearances  of— I,  milk  :  II,  cream  ;  III,  butter ;   IV,  colostrum  of 
mare  ;  V,  colostrum  of  cow  (after  Thanhoffer). 


than  at  present,  it  is  not  safe  to  assume  that  their  chemistry  is 
our  chemistry,  or  their  methods  our  methods.  It  may  be  so ; 
but  let  us  not,  in  our  desire  for  simple  explanations  or  undue 
haste  to  get  some  sort  of  theory  that  apparently  fits  into  our 
own  knowledge,  assume  it  gratuitously,  in  the  absence  of  the 
clearest  proofs,  especially  when  our  failures  on  this  supposi- 
tion are  so  numerous. 

We  may  say,  then,  that  fat  is  not  merely  selected  from  the 
blood,  but  formed  in  the  animal  tissues ;  that  fat  formation 
may  take  place  when  the  food  consists  largely  of  carbohydrates, 
when  it  is  chiefly  proteid,  or  when  proteid  and  fatty.  In  other 
words,  fat  results  from  the  metabolism  of  certain  cells,  which 
is  facilitated  by  the  consumption  of  carbohydrate  and  fatty 
food,  but  is  possible  when  the  food  is  chiefly  nitrogenous.  We 
must,  however,  recognize  differences  both  of  the  species  and 
the  individual  in  this  respect,  as  to  the  extent  to  which  one 
kind  of  food  or  the  other  most  favors  fat  formation  (excre- 
tion). The  use  of  the  adipose  tissue  as  a  packing  to  pre- 
vent undue   escape   of  heat  is  evident  ;   but  more  important 


THE   METABOLISM   OF  THE   BODY.  445 

purposes  are  probably  served,  as  will  appear  from  later  consid- 
erations. 

Pathological. — Corpulence,  or  excessive  fat  formation,  leading 
to  the  hampering  of  respiration,  the  action  of  the  muscles,  and, 
to  a  certain  extent,  many  other  functions  of  the  body,  does  not 
arise  usually  till  after  middle  life,  when  the  organism  has 
seen  its  best  days.  It  seems  to  indicate,  if  we  judge  by  the 
frequency  of  fatty  degeneration  after  disease,  that  the  proto- 
plasm stops  short  of  its  best  metabolism,  and  becomes  de- 
graded to  a  lower  rank ;  for  certainly  adipose  tissue  does  not 
occupy  a  high  place  in  the  histological  scale.  Many  persons 
given  to  excessive  fat  formation  are  fond  of  saccharine  and 
amylaceous  foods ;  but  the  fact  that,  under  the  strictest  diet, 
the  abnormality  can  be  but  moderately  controlled,  shows  that 
the  main  point  is  the  existence  of  the  habit  of  certain  cells 
naturally  to  form  fat,  which,  in  disease,  becomes  exaggerated, 
or  is  taken  up  by  others  that  normally  have  little  share  in 
such  work.  Such  pathological  facts  throw  a  good  deal  of  light 
upon  the  general  nature  of  fat  excretion,  as  it  would  be  better 
to  term  it,  perhaps,  and  seem  to  warrant  the  view  that  we  have 
presented  of  the  metabolic  processes. 

Although  the  nerves  governing  the  secretion  of  milk  have 
not  been  traced,  there  can  be  no  doubt  that  the  nervous  system 
controls  this  gland  also.  The  influence  of  the  emotions  on  both 
the  quantity  and  quality  of  the  milk  in  the  human  subject  and 
in  lower  animals  is  well  known.  There  seems  to  be  no  doubt 
that  milk  of  an  injurious  if  not  absolutely  poisonous  character 
may  be  formed  under  the  influence  of  depressing  or  unusually 
exciting  emotions,  as  grief,  rage,  etc.  We  know  less  about  the 
influence  of  the  nervous  system  in  fat  formation  elsewhere, 
though  it  is  well  enough  established  that  persons  grow  thin 
under  worry  as  well  as  excessive  mental  and  physical  exertion. 
In  the  latter  case,  it  is  not  imjjrobable  that  the  overworked 
muscles  may  draw,  in  some  way,  on  the  stored  fat.  At  the 
same  time,  fat  formation  may  be  interfered  with,  and  be  an  ex- 
pression of  the  unnatural  conditions  generally  that  have  been 
established.  Such  cases  are  too  complex  to  permit  of  being 
comph-tf'ly  unraveled. 

Comparative. — While  breeders  recognize  certain  foods  as 
tending  to  fat  formation  and  others  to  milk  production,  it  is 
interesting  to  note  that  their  experience  shows  that  race  and 
individuality,  even  on  the  male  side,  tell.  The  same  conditions 
being  in  all  respects  observed,  one  breed  of  cows  gives  more 


446  ANIMAL  PHYSIOLOGY. 

and  better  milk  than  another,  and  the  bull  is  himself  able  to 
transmit  this  peculiarity ;  for,  when  crossed  with  other  breeds, 
he  improves  the  milking  qualities  of  the  latter.  Individual 
differences  are  also  well  known. 

The  Metabolic  Processes  concerned  in  the  Formation 
OF  Urea,  Uric  Acid,  Hippuric  Acid,  and  Allied 
Bodies. 

^  Creatin  is  represented  by  the  formula  C4H9N3O2,  and  crea- 
tinin  by  C4H7N3O — that  is,  the  latter  may  be  regarded  as  the 
firmer  dehydrated.  Creatinin  occurs,  as  we  have  seen,  in  urine, 
and  the  question  arises.  Is  the  creatin  of  muscle  the  antecedent 
of  the  creatinin  of  urine  ?  Creatin  when  injected  into  the 
blood  reappears  as  creatinin  in  the  urine ;  but  the  latter  sub- 
stance is  not  increased  by  exercise,  though  the  creatin  of  the 
muscles  is,  while,  like  urea,  creatin  is  augmented  by  a  proteid 
(flesh)  diet.  It  is  not  clear,  then,  that  the  creatin  of  muscle 
has  any  definite  relation  to  the  creatinin  of  urine.  But  crea- 
tin occurs  not  only  in  muscle,  but  in  a  variety  of  other  tis- 
sues, including  the  nervous  ;  in  fact,  it  may  be  regarded  as 
one  of  the  products  of  proteid  metabolism.  Putting  these 
facts  along  with  the  absence  of  urea  itself  from  muscle  and 
many  other  tissues,  there  is  some  probability  in  the  view 
that  creatin  is  one  of  the  antecedents .  of  urea ;  possibly  it  is 
one  of  the  products  which  the  kidneys  directly  convert  into 
urea. 

There  are  several  facts  which  point  to  the  liver  as  being 
the  seat  of  urea  formation:  1.  Leucin,  when  taken  in  large 
quantities,  reappears  in  the  urine  as  urea,  or,  at  all  events,  is 
followed  by  an  increase  in  the  excretion  of  urea  by  the  kid- 
neys. 2.  In  certain  diseases  of  the  liver  (acute  atrophy)  urea 
is  largely  replaced  in  the  urine  by  leucin  and  tyrosin.  Now, 
since  the  consumption  of  much  proteid  matter  is  soon  fol- 
lowed by  an  excess  of  urea  in  the  urine,  and  since  in  such 
cases  it  is  likely  that  a  good  deal  of  leucin  and  its  compan- 
ion, tyrosin,  are  formed  in  the  digestive  tract,  which  we  may 
suppose  are  carried  directly  by  the  portal  blood  to  the  liver, 
the  conclusion  has  been  drawn  from  this  and  the  facts  just 
mentioned,  as  well  as  others,  that  the  liver  is  a  former  of 
urea. 


THE   METABOLISM   OF   THE   BODY.  447 

Urea  may  be  prepared  artificially,  as  represented  by  tlie  fol- 
lowing equations : 

1.  CO<g|^fj  =  C0N,H4+  H,0. 

Ammonium  Urea, 

carbamate. 

2.  CX.XH,  4-  H2O  =  CON2H4. 

Cyanamide. 

3.  CN(0NH4)  =  C0N,H4. 

Ammonium 
cyanate. 

Leuciii  is  amido-caproic  acid  (CH3CH.jCH2CH2CH(NH2) 
CO2H). 

Another  amido-acid,  glycin — 

Amido-acetic  acid, 

when  introduced  into  tbe  digestive  tract,  gives  rise  to  an  in- 
crease of  the  urea  of  the  urine. 

It  will  be  seen  that  ammonia  comjjounds,  both  in  the  labora- 
tory and  apparently  in  the  body,  have  a  formative  relation  to 
urea ;  but  beyond  this  we  can  not  go  very  far  in  furnishing  a 
chemical  explanation  of  the  formation  of  urea  as  a  part  of  a 
series  of  metabolic  processes.  Do  the  kidneys  merely  pick 
out  from  the  blood  and  pass  on  into  the  urinary  tubules  the 
already  formed  urea — i.  e,,  eat,  so  to  speak,  and  then  discharge 
it,  Amoeba-like — or  do  they  manufacture  it  from  bodies  that 
have  gone  on  the  way  a  certain  distance  toward  urea  before 
they  reach  the  kidneys ;  or,  again,  do  they  form  urea  in  some 
such  way  as  the  mammary  gland  constructs  fat  ? 

If  the  ureters  be  tied,  the  renal  arteries  ligatured,  or  the 
kidneys  extirpated,  urea  accumulates  in  the  blood  and  tissues. 
This  might  be  explained  on  the  supposition  that  urea  formed 
elsewhere  was  not  eliminated;  or  that  some  body  related  to 
urea,  and  the  usual  transformations  of  which  are  completed 
in  the  kidneys,  under  these  unwonted  circumstances  becomes 
urea,  either  in  the  tissues  in  which  it  arose  or  elsewhere. 

We  can  not  pronounce  with  certainty  in  favor  of  any  one 
or  all  of  these  conceivable  methods.  We  may  perhaps  assume 
that  creatin  and  jjossibly  other  allied  bodies  are  antecedents  of 
urea ;  that  the  leucin  and  perhaps  the  tyrosin  of  digestion  in 
some  way  give  rise  to  urea ;  and  that  the  liver  and  possibly 
the  spleen  are  organs  in  which  a  portion  of  the  urea  is  formed ; 
that  a  part  of  the  urea  of  urine  is  simply  withdrawn  from  the 
blood  by  the  kidneys ;  but,  as  to  whether  any  part  is  made  by 


448  ANIMAL   PHYSIOLOGY. 

the  latter  in  either  of  the  senses  to  which  we  have  alluded 
above,  is  a  matter  on  which  there  is  very  little  evidence.  It  is 
perhaps  best  to  assume,  at  least,  the  possibility  of  the  truth  of 
both  of  them. 

Uric  Acid. — This  substance  can  be  oxidized  in  the  laboratory 
to  urea,  thus : 

C5H4N4O3  +  H2O  +  O  =  C4N2H,04  +  CN.HiO, 

Uric  acid.  Alloxan.  Urea. 

SO  that  it  has  been  assumed  that  uric  acid  in  the  body  is  a  stage 
short  of  urea,  and  this  seemed  the  more  plausible,  since  it  re- 
places the  latter  in  the  cold-blooded  animals.  But  this  is  not 
entirely  the  case,  for  in  the  frog  urea  is  found  in  the  urine, 
and  our  knowledge  of  this  secretion  in  most  of  them  is  very 
incomplete ;  moreover,  in  the  birds,  representing  the  very  great- 
est degree  of  activity  and  the  highest  oxidative  capacity,  uric 
acid  is  the  principal  nitrogenous  body  of  the  urine,  and  not 
urea. 

Pathological. — "When  there  is  excessive  indulgence  by  man 
in  proteid  foods,  etc.,  the  uric  acid,  normally  small  in  quantity, 
is  increased  greatly,  and  may  give  rise  to  depositions  of  urates 
about  the  joints. 

It  seems  best  to  regard  uric  acid  as  the  result  of  proteid 
metabolism  when  of  a  certain  type,  and  urea  as  the  outcome 
of  the  vital  processes  of  animals  of  a  distinct  physiological 
type. 

Evolution. — There  is  a  good  deal  of  paleontological  evidence 
which  points  to  a  phylogenetic  (ancestral)  relation  between 
birds  and  reptiles ;  hence  the  many  points  of  functional  resem- 
blance between  these  groups  of  creatures  now  so  different  in 
form  and,  in  some  respects,  in  functions.  The  excessive  pro- 
duction of  uric  acid  (uric-acid  diathesis)  can  be  understood  in 
the  light  of  physiological  reversion.  It  is  well  known  that  this 
diathesis  is  hereditary — that  is  to  say,  the  metabolic  habit  of 
excessive  production  of  uric  acid  may  be  imparted  to  offspring. 

Hippuric  Acid. — Among  the  herbivora  hippuric  acid  may  be 
said  to  replace  uric  acid.  In  the  laboratory  this  acid  may  be 
made  from  benzoic  acid  and  glycocol  (glycin),  thus : 

CeH5.C00H  +  Holc>^^^  =  CH,<g^g§^^^«^«  +  H«0. 

Benzoic  acid.  Glycin.  Hippuric  acid. 

It  is  interesting  to  note  that,  when  benzoic  acid  is  swallowed 
by  man,  hippuric  acid  appears  in  the  urine ;  and  it  is  said  that 


THE   METABOLISM   OF   THE   BODY.  449 

■u-hen  blood  containing  benzoic  acid  is  mixed  witli  fresh  minced 
kidney  it  is  transformed  to  liij)puric  acid.  Hay  contains  a  ben- 
zoic compound,  so  that  it  is  not  difl&cult  to  find  a  starting-point 
for  the  bippuric  acid  of  the  herbivora.  In  these  instances  it  is 
assumed  that  glycin  is  added  in  the  kidneys ;  but,  as  a  matter 
of  fact,  this  substance  has  not  as  yet  been  found  anywhere  in 
the  body,  though  it  is  possible  to  conceive  that,  like  peptone, 
it  might  be  formed  and  disappear  (be  used)  as  fast  as  gen- 
erated. 

The  above  is  one  of  the  clearest  cases  favoring  the  view  that 
the  chemical  j^rocesses  of  the  body  do  really  very  much  resem- 
ble those  of  the  laboratory.  But,  considering  the  difficulty  as 
to  glycin,  and  that  the  liver  also  can  form  hippuric  acid  under 
similar  circumstances  (those  mentioned  above),  and  that  there 
are  several  laboratory  methods  for  the  synthesis  of  hippuric 
acid,  it  behooves  us  to  be  cautious  even  in  this  case,  the  chain 
of  facts  being  by  no  means  complete. 

Of  the  origin  of  the  allied  bodies — xanthin,  etc. — or  their 
fate  and  i^urpose,  we  know  very  little.  Their  resemblance 
chemically  to  certain  alkaloids  in  tea,  coffee,  etc.,  is  suggestive. 
Are  they  natural  stimulants  ? 

The  Study  of  the  Metabolic  Processes  by  other 
Methods. 

It  will  be  abundantly  evident  that  our  attempts  to  follow 
the  changes  which  the  food  undergoes  from  the  time  of  its 
introduction  into  the  blood  until  it  is  removed  in  altered  form 
from  the  body  has  not  been  as  yet  attended  with  great  success. 
It  is  possible  to  establish  relations  between  the  ingesta  and  the 
egesta,  or  the  income  and  output  which  have  a  certain  value. 
It  is  important,  however,  to  remember  that,  when  quantitive 
estimations  have  to  be  made,  a  small  error  in  the  data  becomes 
a  large  error  in  the  final  estimate;  one  untrue  assumption 
may  vitiate  completely  all  the  conclusions. 

In  discussing  tlie  subject  we  shall  introduce  a  number  of 
tables,  but  it  will  be  remembered  that  the  results  obtained  by 
one  investigator  differ  from  those  obtained  by  another;  and 
that  in  all  of  them  there  are  some  deviations  from  strict  ac- 
curacy, so  that  the  results  must  be  regarded  as  only  approxi- 
mately correct.  It  is,  however,  we  tliink,  better  to  examine 
such  statistical  tables  of  analyses,  etc.,  than  to  rely  on  the 
mere  verbal    statement  of   certain  results,  as  it  leaves  more 

29 


450 


ANIMAL  PHYSIOLOGY. 


room  for  individual  judgment  and  tlie  assimilation  of  such 
ideas  as  they  may  suggest  outside  of  the  subject  in  hand. 

The  subject  of  diet  is  a  very  large  one ;  but  it  will  be  evi- 
dent on  reflection  that,  before  an  average  diet  can  be  prescribed 
on  any  scientific  grounds,  the  composition  of  the  body  and 
the  nature  of  those  processes  on  which  nutrition  generally 
depends  must  be  known.  Not  a  little  may  be  learned  by  an 
examination  of  the  behavior  of  the  body  in  the  absence  of  all 
diet,  when  it  may  be  said  to  feed  on  itself,  one  tissue  sup- 
plying another.  All  starving  animals  are  in  the  nature  of  the 
case  carnivorous. 


Composition  of  the  Mammalian  Body. 


Adult  man. 

New-born  child. 

Skeleton 

Muscles.                 

15-9 
41-8 
1-7 
7-2 
18-2 
6-9 
1-9 

17-7 
22-9 

Thoracic  viscera 

30 

Abdominal  viscera 

11-5 

Fat 

|20-0 
lo-8 

Skin 

Brain.             .        

For  the  cat  an  analysis  has  yielded  the  following : 

Muscle  and  tendons 45*0  per  cent. 

Bones 147 

Skin 12-0 

Mesentery  and  adipose  tissue 3'8        " 

Liver 4-8 

Blood  (escaping  at  death) 6'0        " 

Other  organs  and  tissues 137        " 

The  large  proportional  weight  of  the  muscles,  the  similarly 
large  amount  of  blood  they  receive,  which  is  striking  in  the 
case  of  the  liver,  also  suggest  that  the  metabolism  of  these 
structures  is  very  active,  and  we  should  expect  that  they 
would  lose  greatly  during  a  starvation  period.  It  is  a  matter 
of  common  observation  that  animals  do  lose  weight  and  grow 
thin  under  such  circumstances,  which  means  that  they  must 
lose  in  the  muscles  and  the  adipose  tissue.  Attempts  have  been 
made  to  determine  exactly  the  extent  to  which  the  various 
tissues  do  suffer  during  complete  abstinence  from  food,  and 
this  may  be  gathered  from  the  table  given  below. 

Starvation. — A  cat  weighing  2,464  grammes  lost  before  death 
on  the  eighteenth  day  1,197  grammes  in  weight.     Of  this  about 


THE  METABOLISM   OP  THE   BODY.  451 

204  grammes  (17  per  cent)  was  in  albuminous  matter;  132 
grammes  (11  per  cent)  loss  of  fat ;  863  grammes  loss  of  water,  71 
per  cent  of  the  total  body  weight. 

It  will  not  be  forgotten  that  about  three  fourths  of  the 
body  is  made  up  of  water,  so  that  the  loss  of  so  large  an 
amount  of  the  latter  during  starvation  is  not  wholly  inexpli- 
cable. 

In  the  case  of  another  cat  during  a  starvation  period  of  thir- 
teen days  734  grammes  of  solids  were  lost,  of  which  248  grammes 
were  fat  and  118  muscle — i.  e.,  about  one  half  of  the  total  loss 
was  referable  to  these  two  tissues  alone. 

The  other  tissues  lost  as  follows,  estimated  as  dry  solids : 

Adipose  tissue 97"0  per  cent. 

Spleen 631 

Liver 56*6 

Muscles 30-2 

Blood 17-6 

Brain  and  spinal  cord O'O         " 

It  will  be  observed  (a)  that  the  loss  of  the  fatty  tissue  was 
greatest,  nearly  all  disappearing ;  (b)  that  the  glandular  struct- 
ures were  next  in  order  the  greatest  sufferers;  (c)  that  after 
them  come  the  skeletal  muscles. 

Now,  it  has  been  already  seen  that  these  tissues  all  engage 
in  an  active  metabolism  with  the  exception  of  adipose  tis- 
sue. 

The  small  loss  on  the  part  of  the  heart,  which  is  still  less 
for  the  nervous  system,  is  especially  noteworthy.  Two  ex- 
planations are  possible.  On  the  one  hand,  we  may  suppose 
that  their  metabolism  is  active,  but  that  they  feed  in  some 
sense  on  the  other  tissues,  and  thus  preserve  themselves  from 
loss  of  substance.  But,  again,  we  have  seen  that  the  functional 
activity  of  the  nervous  system  is  not  accompanied  by  any  very 
marked  chemical  phenomena  that  we  have  succeeded  in  detect- 
ing, at  all  events ;  and  little  is  known  of  the  metabolism  of 
the  heart  itself.  Do  its  pulsations  from  long  habit  go  on  with 
little  expenditure  of  energy,  as  is  the  case  with  the  automatic 
workman  engaged  in  a  narrow  round  of  duty  ?  Has  the  nerv- 
ous system  in  the  course  of  its  evolution  acquired  the  power 
<jf  accom[>lishing  much,  like  persons  with  special  aptitudes, 
witli  little  loss  of  energy  ?  It  is  not  possible  to  decide  exactly 
wh-tt  share  these  several  factors  may  take ;  though  that  they 
all  and  others  as  yet  unrecognized  do  share  in  the  general 
result  seems  prcjbable.     The  loss  of  adipose  tissue  is  so  striking 


452  ANIMAL   PHYSIOLOGY. 

that  we  must  regard  it  as  an  especially  valuable  storeliouse  of 
energy,  available  as  required. 

When  we  turn  to  the  urine  for  information,  it  is  found  that 
in  the  above  case  27  grammes  of  nitrogen  were  excreted  and 
almost  entirely,  of  course,  in  the  form  of  urea ;  and  since  the 
loss  of  nitrogen  from  the  muscles  amounted  to  15  grammes,  it 
will  appear  that  more  than  one  half  of  the  nitrogenous  excreta 
is  traceable  to  the  metabolism  of  muscular  tissue.  It  has  been 
customary  to  account  for  the  urea  in  two  ways :  first,  as  derived 
from  the  metabolism  of  the  tissues  as  such,  and  continuously 
throughout  the  whole  starvation  period ;  and,  secondly,  from  a 
stored  surplus  of  proteid  which  was  assumed  to  be  used  up 
rapidly  during  the  early  days  of  the  fasting,  and  was  the  luxus 
consumption  of  certain  investigators. 

Comparative. — Experiment  has  shown  that  the  length  of 
time  during  which  different  groups  of  animals  can  endure  com- 
plete withdrawal  of  food  is  very  variable,  and  this  applies  to 
individuals  as  well  as  species.  That  such  differences  hold  for 
the  human  subject  is  well  illustrated  by  the  history  of  the  sur- 
vivors of  wrecks.  Making  great  allowances  for  such  devia- 
tions from  any  such  results  as  can  be  established  by  a  limited 
number  of  experiments,  it  may  be  stated  that  the  human  being 
succumbs  in  from  twenty-one  to  twenty-four  days ;  dogs  in 
good  condition  at  the  outset  in  from  twenty-eight  to  thirty 
days ;  small  mammals  and  birds  in  nine  days,  and  frogs  in 
nine  months.  Very  much  depends  on  whether  water  is  allowed 
or  not — life  lasting  much  longer  in  the  former  case.  The  very 
young  and  the  very  old  yield  sooner  than  persons  of  middle 
age.  It  has  been  estimated  that  strong  adults  die  when  they 
lose  ^0"  of  the  body  weight.  Well-fed  animals  lose  weight 
more  rapidly  at  first  than  afterward. 

Diet. — All  experinients  and  observations  tend  to  show  that 
an  animal  can  not  remain  in  health  for  any  considerable  period 
without  having  in  its  food  proteids,  fats,  carbohydrates,  and 
salts ;  indeed,  sooner  or  later  deprivation  of  any  one  of  these 
will  result  in  death. 

Estimates  based  on  many  observations  have  been  made  of 
the  proportion  in  which  these  substances  should  enter  into  a 
normal  diet.  In  the  nature  of  the  case,  for  a  creature  like 
man  especially,  whose  adaptive  power  is  so  great  that  he  can 
learn  to  live  under  a  greater  variety  of  conditions  than  any 
other  animal,  any  figures  on  this  subject  must  be  interpreted 
as  being  but  a  very  general  statement  of  the  case. 


THE  METABOLISM  OP  THE  BODY. 


453 


We  give  another  series  of  tables,  founded  on  experiments 
b}^  different  investigators  from  which  a  number  of  conclusions 
may  be  drawn : 

The  Requirements  of  an  Adult  Man  for  Twenty  four  Hours. 


FOOD  IN  GKAMMES. 

At  rest. 
(Playfair.) 

Moderate  work. 
(Moleschott.) 

Laborious  work. 

(Playfair.) 

(V.  Pettenkofer 
and  V.  Voil.) 

Proteids 

Fats 

Carbohydrates 

70-87 

28-35 

310-20 

130 

84 

404 

155-92 

70-87 
567-50 

137 
117 
352 

Ingesta  of  an  Advlt 

work 

ing 

moder 

ately  ( V 

ierordt) 

• 
c 

H          1 

N 

0 

120  gramme?  albumin,  containing 
90  grammes  tats,  containing  . 

04-18 
70-20 

146-82 

8-60 
10-26 
20-33 

18-88 

28-34 

9-54 

330  grammes  starch,  containing 

102-85 

Total  

281-20      39-19     1 

18-88 

200-73 

It  has  further  been  estimated  that  744  grammes  of  oxygen 
are  respired,  2,818  grammes  water  drunk,  and  32  grammes  of 
salts  consumed. 

The  total  ingesta  have  been  estimated  at  4^  of  the  body 
weight ;  and  the  daily  metabolism  of  the  body  is  calculated  as 
leading  to  the  transformation  of  G  per  cent  of  the  water,  0  per 
cent  of  the  fat,  1  per  cent  of  the  proteids,  and  4  per  cent  of 
the  salts  of  the  body. 

The  Egesta  of  an  Adult  ivorking  moderate}]]. 


HaO 

C 

248-8 

2-0 

9-8 

20-0 

H 

'3-3 
3-0 

N 

0 

By  res}»iration 

By  tran.-^iiiration 

Bv  urine 

330 

660 
1,700 

128 

is-s 

30 

651-15 

7-2 

11-1 

By  fa'ces 

12-0 

Total 

2,818 

281-2 

6-3 

18-8 

081-45 

If  wo  lay  down  the  rule  as  has  been  done,  that  the  nitrog- 
enous shouhl  bear  the  proportion  of  I  to  '•\\-'^  of  non-ni- 
trogenous, an  inspection  of  the  following  analytical  table 
will  show  how  these  various  food-stulfs  conform  to  such  an 
estimate. 


454 


ANIMAL  PHYSIOLOGY. 


For  the  herbivora  from  1  to  8-9  (some  claim.  1  to  5-|)  is  the 
estimated  ratio  of  nitrogenous  to  non-nitrogenous  foods  : 


Nitro. 

Non-nitro. 

Nitro. 

Non-nitro 

Veal 

10 

1 

Human  milk  .....  . 

...     10 

87 

Hare's  flesh 

10 

10 

3 
17 

Wheaten-flour 

..  .     10 

46 

Beef 

Oatineal 

...     10 

50 

Lentils 

10 

21 

Rye-meal 

...     10 

57 

Beans 

10 

22 

Barley-meal 

...     10 

57 

. .    ..     10 

23 

White  potatoes 

...     10 

86 

Mutton 

..     10 

27 

Blue  potatoes 

...     10 

115 

Pork 

10 

30 

Rice 

...     10 

123 

Cow's  milk 

10 

30 

Buckwheat- meal.. . . 

...     10 

130 

One  investigator  estimates  that  in  order  to  get  the  one  hun- 
dred and  thirty  grammes  of  proteids  required  by  an  adult  man 
engaged  at  moderate  labor,  the  following  proportions  of  differ- 
ent kinds  of  foods  must  be  eaten : 


Grammes. 

Cheese 388 

Lentils 491 

Peas 583 

Beef 614 

Eggs 968 


Grammes. 

Wheaten  bread 1,444 

Rice 2,562 

Rye-bread 2,875 

Potatoes 10.000 


One  conclusion  that  is  most  obvious  from  the  above  is  that, 
in  order  to  obtain  the  amount  of  proteids  needed  from  certain 
kinds  of  food,  enormous  quantities  must  be  eaten  and  digested  ; 
and  as  there  would  be  in  such  cases  an  excess  of  carbohydrates, 
fats,  etc.,  unnecessary  work  is  entailed  upon  the  organism  in 
order  to  dispose  of  this. 


Feeding  Experiments  {Ingesta  and  Egesta). 

If  all  that  enters  the  body  in  any  form  be  known,  and  all 
that  leaves  it  be  equally  well  known,  conclusions  may  be  drawn 
in  regard  to  the  metabolism  the  food  has  undergone.  The  pos- 
sible sources  of  fallacy  will  appear  as  we  proceed. 

The  ingesta,  in  the  widest  sense,  include  the  respired  air  as 
well  as  the  food. ;  though  from  the  latter  must  be  subtracted 
the  waste  (undigested)  matters  that  appear  in  the  faeces.  The 
ingesta  when  analyzed  include  carbon,  hydrogen,  oxygen,  ni- 
trogen, sulphur,  phosphorus,  water,  and  salts,  their  source 
being  the  atmosphere  and  the  food-stuffs. 

The  egesta  the  same,  and  chiefly  in  the  form  of  carbonic  an- 
hydride, of  water  from  the  lungs,  skin,  alimentary  canal,  and 


THE  METABOLISM   OF   THE   BODY.  455 

kidneys,  of  salts  and  water  from  the  skin  and  kidneys,  and  of 
nitrogen,  cliiefiy  as  urea  almost  wholly  from  the  kidneys.  Usu- 
ally in  exj3erimental  determinations  the  total  quantity  of  the 
nitrogen  of  the  urine  is  estimated.  If  free  nitrogen  plays  any 
part  in  the  metabolic  processes  it  is  unknown. 

A  large  number  of  feeding  experiments  have  been  made  by 
different  investigators,  chiefly,  though  not  exclusively,  on  the 
lower  animals.  Some  such  method  as  the  following  has  usu- 
ally been  pursued :  1.  The  food  used  is  carefully  weighed  and  a 
sample  of  it  analyzed,  so  that  more  exact  data  may  be  obtained. 
2.  The  amount  of  oxygen  used  and  carbonic  anhydride  exhaled, 
as  well  as  the  amount  of  water  given  off  in  any  form,  is  esti- 
mated. 3.  The  amount  of  the  nitrogenous  excreta  is  calculated, 
chiefly  from  an  analysis  of  the  urine,  though  any  loss  by  hair, 
etc.,  is  also  to  be  taken  into  account. 

It  has  been  generally  assumed  that  the  nitrogen  of  the  ex- 
creta represents  practically  the  whole  of  that  element  entering 
the  body.     This  has  been  denied  by  some  investigators. 

The  respiratory  products  have  been  estimated  in  A^arious 
ways.  One  consists  in  measuring  the  quantity  of  oxygen  sup- 
plied to  the  chamber  in  which  the  animal  under  observation  is 
inclosed,  and  analyzing  from  time  to  time  samples  of  the  air  as 
it  is  drawn  through  the  chamber ;  and  on  these  results  the  total 
estimates  are  based. 

It  will  appear  that  even  errors  in  calculating  the  composi- 
tion of  the  food — and  this  is  very  variable  in  different  samples, 
e.  g.,  of  flesh  ;  or  any  errors  in  the  analysis  of  the  urine,  or  in 
the  more  difficult  task  of  estimating  the  respiratory  products, 
may,  when  multiplying  to  get  the  totals,  amount  to  serious  de- 
partures from  accuracy  in  the  end ;  so  that  all  conclusions  in 
such  a  complicated  case  must  be  drawn  with  the  greatest  cau- 
tion. But  it  can  not  be  doubted  that  such  investigations  have 
proved  of  much  practical  and  some  scientific  value.  The  labor 
they  entail  is  enormous. 

Proteid  Metabolism, — If  we  conceive  of  a  structural  unit  or 
cell  as  wiivhi  \\])  of  a  genuine  protoplasm  constituting  its  mesh- 
work  and  holding  in  the  interstices  certain  substances  that  are 
not  part  of  itself,  strictly  speaking,  the  question  arises.  Are 
these  latter  used  up  in  the  metabolic  process  as  such,  or  do  they 
become  a  part  of  the  true  protoplasm  before  they  undergo  the 
changes  refoi-red  to  above?  Some  writers  speak  of  "organ 
albumin  "  and  "  circulating  albumin,"  and  they  believe  that  the 
latter,  by  whicli  is  meant  the  proteid  material  found  every- 


456  ANIMAL   PHYSIOLOGY. 

where  in  the  fluids  of  the  body,  as  opposed  to  the  former  as 
constituting  organized  tissues,  undergoes  clianges  of  a  retro- 
grade kind  without  ever  becoming  organ  albumin,  while  the 
term  luxus  consumption  was  applied  to  the  metabolism  of  pro- 
teids  in  the  blood.  The  latter  is  not  now  believed  to  occur. 
But  whether  a  portion  of  the  urea  that  represents,  in  the  main, 
the  results  of  proteid  metabolism  is  not  derived  from  the 
metabolism  of  the  material  in  the  interspaces  of  the  tissues 
(circulating  proteids  on  which  the  cells  are  supposed  to  act 
and  in  which  they  effect  changes  without  making  these  pro- 
teids a  part  of  themselves),  is  uncertain. 

Nitrogenous  Equilibrium.^It  is  possil^le  to  so  feed  an  animal, 
say  a  dog,  that  the  total  nitrogen  of  the  ingesta  and  egesta 
shall  be  equal ;  and  this  may  be  accomplished  without  the  ani- 
mal losing  or  gaining  weight  appreciably  or  again  while  he  is 
gaining.  If  there  be  a  gain,  it  can  usually  be  traced  to  the 
formation  of  fat,  so  that  the  proteid,  we  may  suppose,  has 
been  split  up  into  a  part  that  is  constructed  into  fat  and  a 
part  Avhich  is  represented  by  the  urea,  the  fat  being  either  used 
up  or  stored  in  the  body.  Moreover,  an  analysis  of  a  pig  that 
had  been  fed  on  a  fixed  diet,  and  a  comparison  made  with  one 
of  the  same  litter  killed  at  the  commencement  of  the  experi- 
ment, showed  that  of  the  dry  nitrogenous  food  only  about 
seven  per  cent  in  this  animal  and  four  per  cent  in  the  sheep 
had  been  laid  away  as  dry  proteid.  It  is  perfectly  plain,  then, 
that  proteid  diet  does  not  involve  only  proteid  construction 
within  the  body. 

Comparative. — The  amount  of  flesh  which  a  dog,  being  a  car- 
nivorous animal,  can  digest  and  use  for  the  maintenance  of  his 
metabolic  processes  is  enormous ;  though  it  has  been  learned 
that  ill-nourished  dogs  can  not  even  at  the  outset  of  a  feeding 
experiment  of  this  kind  maintain  the  equilibrium  of  their  body 
weight  on  a  purely  flesh  diet  (fat  being  excluded).  They  at 
once  commence  to  lose  weight — i.  e.,  they  draw  upon  their  own 
limited  store  of  fat. 

The  digestion  of  herbivora  being  essentially  adapted  to  a 
vegetable  diet,  they  can  not  live  at  all  upon  flesh,  while  a  dog 
can  consume  for  a  time  Avithout  manifest  harm  ^  to  ^V  o^  its 
body-weight  of  this  food. 

Man,  when  fed  exclusively  on  meat  soon  shows  failure,  he 
being  unable  to  digest  enough  to  supply  the  needed  carbohy- 
drates, etc.  But  the  large  amount  of  urea  in  the  urine  of  car- 
nivorous animals  generally,  and  the  excess  found  in  the  urine 


THE  METABOLISM   OF   THE  BODY.  457 

of  man  when  feeding  largely  on  a  flesh  diet,  show  that  the  pro- 
teid  metabolism  is  under  such  circumstances  very  active. 

It  is  also  a  well-known  observation  that  carnivorous  ani- 
mals (dogs)  are  more  active  and  display  to  a  greater  extent 
their  latent  ferocity,  evidence  of  their  descent  from  wild  car- 
nivorous progenitors,  when  like  them  they  feed  very  largely  on 
flesh.  The  evidence  seems  to  point  pretty  clearly  to  the  con- 
clusion that  a  nitrogenous  (flesh)  diet  increases  the  activity  of 
the  vital  processes  of  the  body,  and  especially  the  proteid  me- 
tabolism. 

Some  have  explained  this  result  on  the  assumption  that 
such  diet  led  to  an  increase  in  the  red  corpuscles  of  the  blood, 
and  hence  in  the  oxygen-supply ;  but  mere  abundance  of  sup- 
ply will  never  of  itself  explain  results  in  a  living  organism.  It 
may  be  and  probably  is  true  that  such  a  diet  augments  the 
activity  of  the  oxidative  processes,  but  the  reason  of  this  lies 
deeper,  we  think,  than  the  explanations  as  yet  offered  assume. 
That  an  excess  of  proteids  may  be  stored,  as  it  seems,  is  true  of 
fats  and  carbohydrates,  to  be  used  in  the  hour  of  need,  seems 
not  improbable,  though  this  has  not  as  yet  been  shown  to  be 
the  case.  But  in  all  these  considerations  it  must  be  borne  in 
mind  that  the  metabolic  processes  go  on  in  the  tissues  and  not 
in  the  blood,  and  probably  not  in  the  lymph.  Not  that  these 
fluids  (tissues)  are  without  their  own  metabolic  processes  for 
and  by  themselves ;  but  what  is  meant  to  be  conveyed  is  that 
the  metabolic  processes  of  the  body  generally  do  not  take  placo 
in  the  blood. 

The  Effects  of  Gelatine  in  the  Diet.— Actual  experiment  shows 
that  this  substance  can  not  take  the  place  of  proteid,  though  it 
also  makes  it  evident  that  less  of  the  latter  suffices  when  mixed 
with  a  certain  proportion  of  gelatine ;  and  it  has  been  suggested 
that  it  is  split  up  into  a  fatty  portion  and  urea,  and  that  it  thus, 
by  aiding  in  the  formation  of  fat,  preserves  some  of  the  proteid 
for  other  uses  than  fat  construction.  This  theory,  however,  is 
not  well  suljstantiated.  It  will  be  borne  in  mind  tliat  ordinary 
flesh  contains,  as  we  find  it  naturally  in  the  carcass,  not  only 
some  fat,  but  a  good  deal  of  fibrous  tissue,  which  can  be  con- 
verted by  hfuting  info  gf^latine. 

Fats  and  Carbohydrates. — It  is  a  matter  of  common  observa- 
tion and  of  movo  exact  exx^eriment  that  even  a  carnivorous  ani- 
mal tlirives  better  on  a  diet  of  fat  and  ](!an  meat  tlian  on  kiun 
flesh  alone.     Tlnis,  it  lias  Ijcen  f(Miiid  tliat  nitrogenous  equi- • 
librium  was  as  readily  establislK^d  Ijy  a  dna  mixture  of  fat  and 


458  ANIMAL   PHYSIOLOGY. 

lean  as  upon  twice  the  quantity  of  lean  flesh  alone.  It  is  plain, 
then,  that  the  metabolism  is  actually  slowed  by  a  fatty  diet. 
When  an  animal  is  given  but  little  fat,  none  whatever  is  laid 
up,  but  all  the  carbon  of  the  fat  can  be  accounted  for  in  the 
excreta,  chiefly  as  carbonic  anhydride.  Again,  the  fatty  por- 
tion remaining  constant,  it  has  been  found  that  increasing  the 
proteid  leads  not  to  a  storage  of  the  carbon  of  the  proteid  ex- 
cess, but  to  an  increased  consumption  of  this  element.  It  is 
then  possible  to  understand  how  excessive  consumption  of  pro- 
teids  may  lead,  as  seems  to  be  the  case,  to  the  disappearance  of 
fat  and  loss  of  weight,  so  that  a  proteid  diet  increases  not  only 
nitrogenous  but  non-nitrogenous  metabolism.  That  carbohy- 
drates mixed  with  a  due  proportion  of  the  other  constituents 
of  a  diet  do  increase  fat  formation  is  well  established ;  though 
there  is  no  equally  well-grounded  explanation  of  how  this  is 
accomplished.  Upon  the  whole,  it  seems  most  likely  that  fat 
can  be  directly  formed  from  carbohydrates,  or,  at  all  events, 
that  they  directly  give  rise  to  fat  if  they  are  not  converted 
themselves  into  that  substance. 

Comparative. — It  is  found  that  there  are  relations  between 
the  food  used  and  the  quantity  of  carbonic  dioxide  expelled 
which  are  instructive.  The  formula  following  show  the  amount 
of  oxygen  necessary  to  convert  a  starch  and  a  fat  into  carbonic 
anhydride  and  water : 

1.  C6H,o05  +  Ou  =  0(CO,)  +  5(H20). 

2.  C57H104O6  +  0,eo  =  57(002)  +  o2{Jl,0). 

It  will  be  observed  that  in  the  first  case  the  oxygen  used  to 
oxidize  the  starch  has  all  reappeared  as  OO2,  while  in  the  sec- 
ond only  114  parts  out  of  IGO  so  reappear.  As  a  matter  of  fact, 
more  of  the  oxygen  used  does  in  herbivora  reappear  as  OO2, 
and  less  as  water,  while  the  reverse  holds  for  the  carnivora,  the 
proportion  being,  it  is  estimated,  as  from  90  to  GO  per  cent. 
This  is  to  be  explained  by  the  character  of  the  food  in  each 
instance,  for  this  relation  no  longer  holds  during  fasting,  when 
the  herbivorous  animal  becomes  carnivorous  in  the  sense  that 
it  consumes  its  own  tissues. 

To  most  persons  the  carbohydrates  are  more  digestible  than 
fats,  though  they  have  less  potential  energy,  as  will  shortly 
be  seen. 

The  Effects  of  Salts,  Water,  etc.,  in  the  Diet. — We  have  already 
considered  how  salts  in  the  form  of  condiments  may  beneficially 
influence  the  digestion ;  but,  when  we  come  to  inquire  as  to  the 


THE   METABOLISM   OF   THE   BODY.  459 

part  they  play  when  introduced  into  the  blood,  we  soon  find 
that  our  knowledge  is  very  limited. 

Sulphur,  and  especially  phosphorus,  seem  to  have  some  im- 
portant use  which  quite  eludes  detection.  It  is  important  to 
remember  that  certain  salts  are  combined  with  proteids  in  the 
body,  possibly  to  a  greater  extent  than  we  can  learn  from  the 
mere  analysis  of  dead  tissues. 

Pathological. — The  withdrawal  of  any  of  the  important  salts 
of  the  body  soon  leads  to  disease,  clear  evidence  in  itself  of  their 
great  importance.  This  is  notably  the  case  in  scurvy,  in  which 
disease  the  blood  seems  to  be  so  disordered  and  the  nutrition 
of  the  vessel-walls  so  altered  that  the  former  (even  some  of  the 
blood-cells)  passes  through  the  latter. 

"Water. — The  use  of  water  certaiidy  has  a  great  influence 
over  the  metabolic  processes  of  the  body.  The  temjjorary  ad- 
dition or  withdrawal  of  even  a  few  ounces  of  water  from  the 
regular  supply  of  a  dog  in  the  course  of  a  feeding  experiment 
greatly  modifies  the  results  obtained  for  the  time.  It  is  well 
known  that  increase  of  water  in  the  diet  leads  to  a  correspond- 
ing increase  in  the  amount  of  urea  excreted.  It  is  likely  that 
even  yet  we  fail  to  appreciate  the  great  part  which  water  plays 
in  the  animal  economy. 

The  Energy  of  the  Animal  Body. 

As  already  explained,  we  distinguish  between  potential  or 
latent  and  actual  energy.  All  the  energy  of  the  body  is  to  be 
traced  to  the  influence  of  the  tissues  upon  the  food.  Energy 
may  be  estimated  as  mechanical  work  or  as  heat,  and  the 
one  may  be  converted  into  the  other.  All  the  processes  of 
the  organism  involve  chemical  changes,  and  a  large  propor- 
tion of  these  are  of  the  nature  of  oxidations ;  so  that,  speak- 
ing broadly,  the  oxidations  of  the  animal  body  are  the  sources 
of  its  energy  ;  and  in  estimating  the  quantity  of  energy,  either 
as  heat  or  work,  that  a  given  food-stuff  will  produce,  one  must 
consider  whether  the  oxidative  processes  are  complete  or  par- 
tial •  thus,  in  the  case  of  proteid  food,  if  we  suppose  that  the' 
urea  excreted  represents  the  form  in  which  the  oxidative  pro- 
cc-'S.ses  end  or  are  arrested,  we  must,  in  estimating  the  actual 
energy  of  the  proteid,  subtract  the  amount  of  energy  that 
would  })(i  jjrofliu;('d  wci"*;  tlx;  urea  itself  coniplctely  oxidized 
(iHinicd). 

If  the  amount  of  heat  that  a  Ijfjdy  will  produce  in  its  coin- 


460 


ANIMAL  PHYSIOLOGY. 


bustion  be  known,  then  by  the  law  of  the  conversion  and  equiv- 
alence of  energy  the  mechanical  equivalent  can  be  estimated  in 
that  particular  case. 

The  heat-producing  power  of  different  substances  can  be 
directly  learned  by  ascertaining  the  extent  to  which,  when  fully 
burned  (to  water  and  carbonic  anhydride),  they  elevate  the 
temperature  of  a  given  volume  of  water  ;  and  this  can  at  once 
be  translated  into  its  mechanical  equivalent  of  work,  so  that 
we  may  say  that  one  gramme  of  dry  proteid  would  give  rise  to 
a  certain  number  of  gramme-degrees  of  heat  or  kilogramme- 
metres  of  work.  A  few  figures  will  now  shov/  the  relative 
values  of  certain  food-stuffs  : 


1  gramme  proteid 

1  gramme  urea 

Available  energy  of  the  proteid 


Gram.-deg. 


5,103 
735 


4.368 


Kiloinet. 


2,161 
311 


1,850 


The  reason  of  the  subtraction  has  been  explained  above. 

Taking  another  diet  in  regard  to  which  the  estimates  differ 
somewhat  from  those  given  previously,  but  convenient  now  as 
showing  how  equal  weights  of  substances  produce  very  dif- 
ferent amounts  of  energy,  we  find  that — 


100  grammes  proteid  yield 
100  grammes  fat  yield, . .  . 
240  grammes  starch  yield. 

Total 


Gram.-deg. 


436,800 
906,900 

938,880 


2,281,580- 


Kilomet. 


185,000 
384,100 
397,080 


966,780 


In  other  words,  nearly  a  million  kilogramme-metres  of  en- 
ergy are  available  from  the  above  diet  for  one  day,  provided 
it  be  all  oxidized  in  the  body. 

Food-stuffs,  then,  with  the  oxygen  of  the  air,  are  the  body's 
sources  of  energy.  What  are  the  forms  in  which  its  expendi- 
ture appears  ?  We  may  answer  at  once,  heat  and  mechanical 
work ;  for  it  is  assumed  that  internal  movements,  as  those  of 
the  viscera,  and  all  the  friction  of  the  body,  all  its  molecular 
motion,  all  secretive  processes,  are  to  be  regarded  as  finally 
augmenting  the  heat  of  the  body.  Heat  is  lost  by  the  skin, 
lungs,  urine,  and  faeces. 


THE   METABOLISM   OF   THE   BODY.  461 

The  amount  of  work  "which  a  man  or  other  animal  can  do 
on  a  given  diet  may  be  estimated  without  the  same  sources  of 
fallacy  as  attend  the  calculation  of  the  heat  expenditure  ;  for, 
Avhen  an  animal  is  confined  in  a  calometric  chamber,  the  con- 
ditions of  the  normal  metabolism  are  not  observed. 

The  Sources  of  Muscular  Energy. 

Experimental. — Two  physiologists  (Fick  and  Wislicenus)  as- 
cended a  mountain,  noting  the  conditions  under  which  their 
metabolism  was  performed,  and  drew  certain  conclusions  in  re- 
gard to  the  question  now  being  considered.  They  lived  exclu- 
sively on  a  non-nitrogenous  diet  while  the  work  was  being  done, 
and  estimated  the  amount  of  urea  excreted  at  the  same  time. 
Assuming  that  the  urea  does  represent  the  proteid  metabolism 
(oxidation)  which  bore,  of  course,  a  definite  relation  to  the 
energy  available,  it  was  found  that  in  the  case  of  each  of  them 
this  was  only  about  half  enough  to  account  for  the  work  done. 
Even  making  large  allowances  for  error  in  the  estimates,  if 
this  exj)eriment  is  to  be  trusted  at  all,  it  is  plain  that  the 
energy  of  the  muscles  of  the  body  is  not  derivable  from  their 
proteid  metabolism ;  and  there  are  other  facts  which  point  in 
the  same  direction. 

It  is  found,  when  an  isolated  muscle  is  studied,  that  its 
continued  contraction  does  not  produce  nitrogenous  bodies,  but 
very  different  ones,  such  as  carbonic  anhydride.  The  quantity 
of  the  latter  may  be  augmented  many  times  by  work.  But  it 
is  no  longer  believed  that  the  severest  labor  api^reciably  in- 
creases the  secretion  of  urea. 

The  division  of  foods  into  heat-producers  and  tissue-builders 
is  unjustifiable,  as  will  appear  from  what  has  just  been  stated, 
as  well  as  from  such  facts  as  the  production  of  fat  from  proteid 
food,  thus  showing  that  the  latter  is  indirectly  a  producer  of 
carbonic  anliydride,  assuming  that  fat  is  oxidized  into  that 
substance. 

Animal  Heat. 

Tliough  a  large  part  of  tlio  lieat  generated  within  the  body 
is  tracealjle  to  oxidations  taking  plac*;  in  tlie  tissues,  it  is  better 
to  speak  of  the  heat  as  being  the  outcome  of  all  tlio  chemical 
processes  of  the  (organism  ;  and  though  heat  may  ])e  rendered 
latf'nt  in  certain  organs  for  a  time,  in  the  end  it  must  reappear. 
While  all  the  tissues  are  heat-producers  (thermogenic),  the  ex- 


462  ANIMAL  PHYSIOLOGY. 

tent  to  wliicli  they  are  sucli  would  depend,  we  should  suppose, 
upon  the  degree  to  which  they  were  the  seat  of  metabolic  pro- 
cesses ;  and  actual  tests  establish  this  fact.  Thus,  among  glands 
the  liver  is  the  greatest  heat-producer ;  hence  the  blood  from 
this  organ  is  the  warmest  of  the  whole  body.  The  muscles  also 
are  especially  the  thermogenic  tissue. 

The  temperature  of  the  blood  in  the  hepatic  vein  is  warmer 
than  that  in  the  portal,  a  clear  evidence  that  the  metabolism  of 
this  organ  has  elevated  the  temperature  of  the  blood  flowing 
through  it. 

The  temperature  of  the  blood  (its  own  metabolism  being 
slight)  is  a  pretty  fair  indication  of  the  resultant  effect  of  the 
production  and  the  loss  of  heat. 

For  obvious  reasons,  the  temperature  of  different  parts  of 
the  body  of  man  and  other  animals  varies. 

The  statements  of  observers  in  regard  to  the  temperature  of 
various  animals  and  of  different  parts  of  the  body  disagree  in  a 
way  that  would  be  puzzling,  were  it  not  known  how  difficult  it 
is  to  procure  perfectly  accurate  thermometers,  not  to  mention 
individual  differences.  The  axillary  temperature  is  about 
37"5°  C. ;  that  of  the  mouth  a  little  higher,  and  of  the  rectum  or 
vagina  slightly  more  elevated.  The  mean  temperature  of  the 
blood  is  placed  at  39°  C. 

It  is  a  very  striking  fact,  however,  that  the  different  parts 
of  the  body  ordinarily  accessible  by  a  thermometer  vary  so 
little — not  more  perhaps  than  a  degree  or  a  degree  and  a  half. 
The  temperature  of  the  hepatic  vein  has  been  put  down  as  39*7°, 
and  it  contains  the  warmest  blood  of  the  body. 

Comparative. — The  temperature  of  various  groups  of  animals 
has  been  stated  to  be  as  follows :  Gull,  37*8° ;  swallow,  44*03° ; 
dolphin,  35"5°;  mouse,  41"1°;  snakes,  10°  to  12°,  but  higher  in  large 
specimens  (python).  Cold-blooded  animals  have  a  temperature 
a  little  higher  (less  than  1°  C.  usually)  than  the  surrounding  air. 
During  the  swarming  of  bees  the  hive  temperature  may  rise 
from  32°  to  40°.  All  cold-blooded  animals  have  probably  a 
higher  temperature  in  the  breeding-season.  In  our  domestic 
mammals  the  normal  temperature  is  not  widely  different  from 
that  of  man. 

Variations  in  the  average  temperature  are  dependent  on 
numerous  causes  which  may  affect  either  the  heat  produc- 
tion or  heat  loss :  1.  Change  of  climate  has  a  very  slight  but 
real  influence,  the  temperature  being  elevated  a  fraction  of 
a  degree  when   an  individual  travels  from  the  poles  toward 


THE  METABOLISM  OF  THE  BODY, 


463 


the  equator,  and  the  same  may  be  said  of  the  effect  of  the 
temperature  of  a  ^Yarm  summer  day  as  compared  with  a  cokl 
winter  one.  The  wonder  is  that,  considering  the  external 
temperature,  the  variation  is  so  light.  2.  Starvation  lowers 
the  temperature,  and  the  ingestion  of  food  raises  it  slightly, 
the  latter  increasing,  the  former  decreasing,  the  rate  of  the 
metabolic  processes.  3.  Age  has  its  influence,  the  very  young 
and  the  very  old,  in  whom  metabolism  (oxidation)  is  feeble, 
having  a  lower  temperature.  This  especially  applies  to  the 
newly-born,  both  among  mankind  and  the  lower  mammals; 
and,  as  might  be  supposed,  the  temperature  falls  during 
sleejj,  when  all  the  vital  activities  are  diminished.  The  same 
remark  applies  with  greater  force  to  the  hibernating  state 
of  animals.  4.  Very  interesting  are  the  fluctuations  of  tem- 
perature   occurring  daily,  as  shown   by   the  curves   of  Fig. 


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Fig.  aw.— Variations  of  the  daily  temperature  in  health  durinq:  24  hours:  L.,  after  Lieber- 
meister  ;  J.^  after  Jurgenson  (from  Landois). 


340.  It  will  be  noticed  that  the  period  of  greatest  bodily 
warmth  is  between  about  four  and  seven  o'clock  in  the  after- 
noon and  the  minimum  temperature  between  two  and  five  in 
the  morning. 

It  will  be  inferred,  from  the  facts  and  figures  already  cited, 
that  different  kinds  of  food  have  considerably  different  capacity 
for  heat  production.  The  following  estimates  will  still  further 
tend  to  illustrate  this : 

Animal  diet  })roduces 2,770,524  heat-units 

Food  frfe  from  nitrogen 2,059,500      "        " 

Mixed  diet 2,200,200      "         " 

Absence  of  food,  the  heat  amounts  to. .  2,012,810      "        " 
It   i.s   well    known    that   a   man   when   working  not  only 
feol.s   warmer,   but   actually   i)roduces  more    heat.      The    fol- 
lowing figures  will    give   (approximately)    some   definite   in- 


46J,  ANIMAL   PHYSIOLOaY. 

formation  on  this   subject,  the  numbers   denoting   the  heat- 
units  produced : 


RESTING    DAY. 

Eest,  16  hours.  Sleep,  8  hours. 

2470-4  320 

Total,  2790-4 


WORKING   D.4.Y.   . 
Rest,  8  hrs.         Work,  8  hrs.         Sleep,  8  hrs. 
1235-2  216-99  320 


Total,  3724-8 


It  appears  from  a  multitude  of  considerations  that  the  body- 
is  like  a  steam-engine,  producing  heat  and  doing  work  ;  but  it 
is  found  that  while  a  very  good  steam-engine,  as  a  result  of  the 
chemical  processes  going  on  within  it,  converts  -|  of  the  poten- 
tial energy  of  its  supplies  into  mechanical  work,  the  other  ^ 
appearing  as  heat,  the  body  produces  ^  as  work  and  f  as  heat, 
from  its  income  of  food  and  oxygen. 

While  it  is  perfectly  clear  that  it  is  in  the  metabolic  pro- 
cesses of  the  body  that  we  must  seek  for  the  final  cause  of  the 
heat  produced,  it  is  incumbent  on  the  physiologist  to  explain 
the  remarkable  fact  that  the  mammalian  body  maintains, 
under  a  changing  external  temperature  and  other  climatic 
conditions,  and  with  a  varying  diet,  during  rest  and  labor,  a 
temperature  varying  within,  usually,  no  more  than  a  fraction 
of  a  degree  centigrade.  This  we  shall  now  endeavor  to  explain 
in  part. 

The  Regulation  of  Temperature. — It  is  manifest  from  the  facts 
adduced  that  so  long  as  life  lasts  heat  is  being  of  necessity  con- 
stantly produced.  If  there  were  no  provision  for  getting  rid  of 
a  portion  of  this  heat,  it  is  plain  that  the  body  would  soon  be 
consumed  as  effectually  as  if  it  were  placed  in  a  furnace.  We 
observe,  however,  that  heat  is  being  constantly  lost  by  the 
breath,  by  perspiration  (insensible),  by  conduction  and  radia- 
tion from  the  surface  of  the  body,  and  periodically  by  the 
urine  and  fgeces.  We  have  seen  that,  while  heat  is  being  pro- 
duced in  all  the  tissues  and  organs  of  the  body,  some  are  es- 
pecially thermogenic,  as  the  glands  and  muscles.  The  skin 
presents  an  extensive  surface,  abundantly  supplied  with  blood- 
vessels, which  when  dilated  may  receive  a  large  quantity  of 
blood,  and  when  contracted  may  necessitate  a  much  larger  in- 
ternal supply,  in  the  splanchnic  region  especially.  It  is  a  mat- 
ter of  common  observation  that,  when  an  individual  exercises, 
the  skin  becomes  flushed,  and  so  'with  the  increased  production 
of  heat,  especially  in  the  muscles  (see  page  195),  there  is  a  pro- 
vision for  unusual  escape  of  the  surplus ;  at  the  same  time 
sweat  breaks  out  visibly,  or  if  not,  the  insensible  ]3erspiration 


THE  METABOLISM   OF   THE   BODY,  465 

is  generally  increased  ;  and  this  accounts  for  an  additional  in- 
crement of  loss  ;  while  the  lungs  do  extra  work  and  exhale  an 
increased  quantity  of  aqueous  vapor,  so  that  in  these  various 
ways  the  body  is  cooled.  Manifestly  there  is  some  sort  of  co- 
ordination between  the  processes  of  heat  production  and  heat 
expenditure.  The  vaso-motor,  secretory,  and  respiratory  func- 
tions are  modified.  Even  if  an  individual  do  no  work  at  all,  as 
when  in  a  Turkish  bath,  it  becomes  evident,  to  one  submitting 
to  the  experiment  (for  such  it  is  or  may  become),  that  the 
pulse  and  respirations  are  quickened  and  that  there  is  copious 
secretion  of  sweat  following  on  reddening  of  the  skin,  owing 
to  vascular  dilatation.  Exact  quantitative  estimation  of  the 
heat  produced,  as  seen  above,  and  of  the  oxygen  used,  the  car- 
bonic anhydride  and  watery  vapor  exhaled,  shows  that  the 
organs  of  which  we  are  speaking  are  not  only  apparently  but 
actually  doing  more  work.  It  is  usual  to  quote  the  case  of 
Drs,  Fordyce  and  Blagden,  who  learned  to  endure  without 
injury  a  heat  of  127"  C,  (260°  F,),  to  illustrate  the  great  adap- 
tability of  our  own  organism  in  this  respect.  We  may  suppose 
that  the  various  co-ordinations  effected,  chiefly  at  all  events 
through  the  central  nervous  system,  and  not  by  the  direct  ac- 
tion of  the  heat  upon  local  nervous  mechanisms,  or  the  tissues 
themselves  directly,  are  reflexes. 

The  prodiiction  of  heat,  however,  seems  to  be  equally  under 
the  influence  of  the  nervous  system,  though  we  know  less  about 
the  details  of  the  matter, 

A  cold-blooded  animal  differs  from  a  warm-blooded  one  in 
that  its  temperature  varies  with  the  surrounding  medium  more ; 
hence  the  terms  poikilofhermer  and  homoiothermer  for  cold- 
blooded and  warm-blooded,  would  be  appropriate. 

Such  an  animal,  as  a  frog  or  turtle,  may  have  its  chemical 
processes  slowed  or  quickened,  almost  like  those  going  on  in  a 
test-tube  or  crucible,  by  altering  the  temperature.  Very  different 
is  it,  as  we  have  seen,  in  the  normal  state  of  the  animal  with 
any  mammal.  Hence  hibernation  or  an  allied  state  has  become 
a  necessary  protection  for  poikilothermers,  otherwise  they 
wouhl  perish  outright,  and  the  groups  become  extinct  in  north- 
ern latitudes.  Now,  when  a  mammal  is  poisoned  with  curare, 
it  becomes  like  a  poikilothermer.  Like  the  latter,  under  in- 
crease of  temperature,  it  too  uses  more  oxygen  and  produces 
more  carbonic  anhydride.  When  certain  parts  of  the  brain 
are  divided  or  punctun;d,  a  fall,  similar  to  that  observable 
wlicii  curare  is  given,  is  observable. 

30 


^QQ  ANIMAL  PHYSIOLOGY. 

It  is  plain  that  vaso-motor  changes  alone  can  not  explain 
these  effects ;  and,  though  possibly  a  part  of  the  rise  of  tem- 
perature, following  exposure  of  the  naked  body  in  a  cool  air, 
inay  be  accounted  for  by  the  increased  metabolism  of  internal 
organs,  accompanying  the  influx  of  blood  caused  by  constric- 
tion of  the  cutaneous  capillaries,  it  is  probable  that  in  this  as 
in  so  many  other  instances  the  blood  and  circulation  have  been 
credited  with  too  much,  and  the  direct  influence  of  the  nervous 
system  on  nutrition  and  heat  production  overlooked  or  under- 
estimated. The  thermogenic  center  has  not  yet  been  definitely 
located,  though  some  recent  investigations  seem  to  favor  a  spot 
in  or  near  the  corpus  striatum  for  certain  mammals.  Some  in- 
vestigators also  recognize  a  cortical  heat-center.  It  has  been 
suggested  that  we  may  to  advantage  speak  of  a  thermotoxic 
(regulative  of  loss)  and  a  thermogenic  mechanism  (regulative 
of  production),  and  even  a  tliermolytic  or  discharging  mechan- 
ism, 'It  has  been  further  suggested  that  different  nerve-fibers 
may  be  concerned  in  the  actual  work  of  conveying  the  different 
impulses  of  these  respective  mechanisms  to  the  tissues ;  and  the 
whole  theory  has  been  framed  in  accordance  with  the  prevalent 
conception  of  metabolism  as  consisting  of  anabolism  and  ca- 
tabolism,  or  constructive  and  destructive  processes.  But  these 
theories  have  not  yet  been  confirmed  by  experiments  on  ani- 
mals, though  they  are,  in  the  opinion  of  their  authors,  in  har- 
mony with  the  facts  of  fever.  Certainly,  any  theory  that  will 
imply  that  vital  processes  are  more  under  the  control  of  the 
nervous  system  than  has  hitherto  been  taught,  will,  we  think, 
advance  physiology,  as  will  shortly  appear  from  our  own  dis- 
cussion of  the  influence  of  the  nervous  system  on  the  various 
metabolic  processes  generally. 

The  phenomena  observable  in  an  animal  gradually  freezing 
to  death  point  strongly  to  the  direct  influence  of  the  nervous 
system  on  the  production  as  well  as  the  regulation  of  heat. 
The  circulation  must  of  course  be  largely  concerned,  but  it  ap- 
pears as  though  the  nervous  system  refused  to  act  when  the 
temperature  falls  below  a  certain  point.  A  low  temperature 
favors  hibernation,  in  which  we  believe  the  nervous  system 
plays  the  chief  part,  though  the  temperature  in  itself  is  not  the 
determining  cause,  as  we  have  ourselves  proved.  The  fact  that 
the  whole  metabolism  of  a  hibernating  animal  is  lowered,  that 
with  this  there  is  loss  of  consciousness  much  more  profound 
that  in  ordinary  sleep,  of  itself  seems  to  indicate  that  the  nerv- 
ous system  is  at  the  bottom  of  the  whole  matter. 


THE  METABOLISM  OP  THE  BODY.  467 

Pathological.  —  It  is  found  that  many  drugs  and  poisons 
lower  temperature,  acting  in  a  variety  of  ways.  In  certain  dis- 
eases, as  cholera,  the  temperature  may  sink  to  23°  C.  in  extreme 
cases  before  death  supervenes.  When  the  temperature  of  the 
blood  is  raised  6°  C.  (as  in  sunstroke,  etc.),  death  occurs  ;  and  it 
is  well  known  that  prolonged  high  temperature  leads  to  fatty 
degeneration  of  the  tissues  generally.  All  the  evidence  goes  to 
show  that  in  fever  both  the  heat  production  and  the  heat  ex- 
penditure are  interfered  with ;  or,  at  least,  if  not  always,  that 
there  may  be  in  certain  cases  such  a  double  disturbance.  In 
fever  excessive  consumption  of  oxygen  and  production  of  car- 
bon dioxide  occur,  the  metabolism  is  quickened,  hence  its  wast- 
ing (consuming)  effects ;  the  rapid  respiration  tends  to  increase 
the  thirst,  from  the  extra  amount  of  aqueous  vapor  exhaled. 
The  body  is  actually  warmest  during  the  "  cold  stage  "  of  ague, 
when  the  vessels  of  the  skin  are  constricted  and  the  patient 
feels  cold,  because  the  internal  metabolism  is  heightened ;  while 
the  "  sweating  stage  "  is  marked  by  a  natural  fall  of  tempera- 
ture. The  fact  that  the  skin  may  be  dry  and  pale  in  fever 
shows  that  the  thermotoxic  nervous  mechanism  is  at  fault ;  but 
the  chemical  facts  cited  above  (excess  of  COo,  etc.)  indicate  that 
the  thermogenic  mechanism  is  also  deranged. 

Special  Considerations. 

If  the  student  will  now  read  afresh  what  has  been  written 
under  the  above  heading  in  relation  to  the  subject  of  digestion,  it 
will  probably  appear  in  a  new  light.  We  endeavored  to  show 
that,  according  to  that  general  principle  of  correlation  which 
holds  throughout  the  entire  organism,  and  in  harmony  with 
certain  facts,  we  were  bound  to  l)elieve  that  digestion  and  as- 
similation, or,  to  speak  in  other  terms,  the  metabolic  processes 
of  the  various  tissues,  in  a  somewhat  restricted  sense,  were 
closely  related.  Beneath  the  common  observation  that  "  diges- 
tion waits  on  appetite  "  lies  the  deeper  truth  that  food  is  not 
prepared  in  the  alimentary  canal  (digested)  without  some  rela- 
tion to  the  needs  of  the  system  generally.  In  other  words,  the 
voice  of  the  tissues  elsewhere  is  heard  in  the  councils  of  the 
digestive  track,  and  is  regarded ;  and  this  is  effected  chiefly 
through  the  nervous  system.  Gluttony  may  lead  to  vomiting 
or  diarrha;a — plain  ways  of  getting  rid  of  what  can  not  be 
digested.  But  how  is  it  that  a  hungry  man  who  has  been  with- 
out food  for  twenty-four  hours  can  digest  with  ease  a  quantity 


4(58  ANIMAL  PHYSIOLOGY. 

of  food,  taken  at  one  meal,  that  would  otherwise  lead  to  the 
above-noted  attempts  at  its  removal  ?  It  is  a  mistake  to  ex- 
plain the  result  with  reference  to  the  alimentary  tract  alone. 
The  entire  metabolism  of  the  body  has  a  voice  in  the  matter. 
From  this  point  of  view,  the  benefit  of  abstinence  from  spe- 
cific articles  of  diet,  partial  or  complete,  of  taking  at  times 
very  light  meals,  and  much  more  that  experience  warrants, 
receives  an  explanation.  Too  little  attention  seems  to  have 
been  given  to  this  aspect  of  the  subject  that  we  are  now  en- 
deavoring to  present  briefly. 

Until  the  nature  of  metabolism  is  more  completely  under- 
stood, it  will  be  impossible  to  treat  the  subject  of  diet,  either 
in  health  or  disease,  with  such  confidence  as  to  enable  us  to 
prescribe  upon  scientific  principles  alone.  Very  much  must 
still  be  empirical,  the  outcome  of  trial  and  result,  which  is, 
however,  after  all,  experiment  in  a  crude  form  ;  and  individual 
peculiarities  that  are  inscrutable  in  their  nature  will  always  be 
encountered.  Notwithstanding,  if  physicians  will  avail  them- 
selves of  the  best  that  is  known  in  the  realm  of  physiologi- 
cal dietetics,  and  then  contribute  the  results  of  their  observa- 
tions in  accurate  form,  substantial  progress  will  be  made  in 
due  time. 

Evolution. — We  have  already  alluded  to  some  of  those  modi- 
fications in  the  form  of  the  digestive  organs  that  indicate  an 
unexpected  plasticity,  and  impress  the  fact  of  the  close  rela- 
tion of  form  and  function.  The  conversion  of  a  sea-gull  into  a 
graminivorous  bird,  with  a  corresponding  alteration  in  the  na- 
ture of  the  form  of  the  stomach  (it  becoming  a  gizzard),  with 
doubtless  modifications  in  the  digestive  processes,  when  re- 
garded more  closely,  implies  coadaptations  of  a  very  varied 
kind.  These  are  as  yet  but  imperfectly  known  or  understood, 
and  the  subject  is  a  wide  and  inviting  field  for  the  physiolo- 
gist. Darwin  and  others  have  indicated,  though  but  imper- 
fectly, some  of  the  changes  that  are  to  be  regarded  in  animals 
as  correlations  ;  but  in  physiology  the  subject  has  received  but 
little  attention  as  yet.  We  have  in  several  parts  of  this  work 
called  attention  to  it ;  but  the  limits  of  space  prevent  us  doing 
little  more  than  attempting  to  widen  the  student's  field  of 
vision  by  introducing  such  considerations.  The  influence  of 
climate  on  metabolism,  an  undoubted  fact,  has  many  implica- 
tions. 

Any  one  who  keeps  a  few  wild  animals  in  confinement  un- 
der close  observation,  and  endeavors  to  ascertain  how  their 


THE  METABOLISM  OF  THE   BODY.  .  469 

natural,  self-chosen  diet  may  be  varied,  when  confined,  will 
be  astonished  at  the  plasticity  of  their  instincts,  usually  con- 
sidered as  so  rigid  in  regard  to  feeding.  These  facts  help 
one  to  understand  how  by  the  law  of  habit  and  heredity 
each  group  of  animals  has  come  to  prefer  and  flourish  best 
upon  a  certain  diet.  But  habit  itself  implies  an  original 
deviation  some  time,  in  which  is  involved,  again,  plasticity 
of  nature  and  power  to  adapt  as  well  as  to  organize.  With- 
out this,  evolution  of  function  is  incomprehensible ;  but  with 
this  principle,  and  the  tendency  for  what  has  once  been  done 
to  be  easier  of  repetition ;  and,  finally,  to  become  organized, 
a  flood  of  light  is  thrown  upon  the  subject  of  diet,  diges- 
tion, and  metabolism  generally.  On  these  principles  it  is 
possible  to  understand  those  race  differences,  even  individ- 
ual differences,  which  as  facts  must  be  patent  to  all  observ- 
ers. Every  individual's  own  history  will  teach  him  that  he 
can  learn  to  digest  and  assimilate  what  was  once  all  but  a 
poison  to  his  organism ;  so  that  it  becomes  comprehensible 
how  a  Chinaman,  for  example,  can,  not  only  remain  in  health, 
but  do  a  large  amount  of  work  daily  on  a  diet  on  which  the 
ordinary  Englishman  might  well-nigh  starve  before  he  could 
adapt  himself  to  it. 

It  is  also  a  well-established  fact  that  whole  families  crave 
and  seem  to  require  certain  articles  of  diet  in  excess,  as  com- 
pared with  the  majority  —  e.  g.,  a  meat  diet.  In  some  in- 
stances, at  all  events,  this  can  be  traced  to  pathological  excess 
in  the  ancestors.  It  is  important  to  recognize,  however,  that 
while  such  a  diet  upon  the  whole  may  be  the  best  that  can  be 
appropriated  at  the  time,  it  is  associated  with  certain  aberrations 
of  function  which  it  is  desirable  to  correct ;  hence  the  wisdom 
of  withholding  from  such  people,  even  children,  to  a  certain 
extent,  the  meat  which  they  so  much  crave.  The  habit  of  the 
metabolism  may  be  modified.  The  rapid  rate  of  speed  of  the 
metabolic  processes,  which  an  excess  of  such  a  diet  is  apt  to 
beget,  leads  to  various  l)ad  results,  such  as  great  irritability  of 
the  nervous  system,  and  a  general  lack  of  stability  and  equi- 
poise in  the  vital  machine. 

Tlie  principle  of  natural  selection  has  clearly  played  a  great 
part  in  determining  the  diet  of  a  species;  the  surviving  emi- 
grants to  a  new  district  must  be  those  that  can  adapt  to  the  local 
envirrmment  best,  including  the  food  which  the  region  su])])lies. 
Tlie  greater  capability  of  resisting  hunger  and  thirst  in  some 
individuals  of  a  species  implies  gicut  differences  in  tlie  meta- 


470  -  ANIMAL  PHYSIOLOGY. 

bolic  processes,  though  these  are  mostly  unknown  to  us ;  and 
the  same  remark  applies  to  heat  and  cold. 

It  seems  clear  that  hibernation  is  an  acquired  habit  of  the 
whole  metabolism,  with  great  changes  in  the  functional  condi- 
tion of  the  nervous  system  recurring  periodically,  and,  in  fact, 
dependent  on  these,  by  which  certain  large  divisions,  as  the 
reptiles,  amphibians,  and  certain  mammals  among  vertebrates, 
are  enabled  to  escape  individual  death  and  extinction  as  groups. 
We  may  suppose  that,  for  example,  among  invertebrates,  by  a 
process  of  natural  selection,  those  survived  that  could  thus 
adapt  themselves  to  the  environment ;  while,  among  mammals, 
hibernation  may  be  considered  as  a  process  of  reversion,  per- 
haps, for  the  homoiothermer  becomes  very  much  a  poikilo- 
thermer  during  hibernation,  the  latter  again  reverting  to  a 
condition  existing  in  lower  forms,  and  not  wholly  unlike  that 
of  plants  in  winter.  This  can  be  understood  on  the  princi- 
ple of  the  origin  of  higher  from  lower  forms ;  otherwise  it 
is  difficult  to  understand  why  similar  states  of  the  metabolism 
should  prevail  in  groups  widely  separated  in  form  and  func- 
tion. If  all  higher  groups  bear  a  derivative  relation  to  the 
lower,  what  is  common  in  their  nature,  as  we  usually  find 
them,  as  well  as  the  peculiar  resemblances  of  the  metabolism 
of  higher  to  lower  forms  in  sleep,  hibernation,  etc.,  can  be 
understood  in  the  light  of  physiological  reversion. 

The  origin  of  a  homoiothermic  (warm-blooded)  condition 
itself  is  to  be  sought  for  in  the  principle  of  natural  selection. 
It  was  open  to  certain  organisms,  we  may  assume,  either  to 
adapt  to  a  temperature  much  below  that  of  their  blood,  or  to 
hibernate;  failing  to  make  either  adaptation  would  result  in 
death ;  and  gradually,  no  doubt,  involving  the  death  of  num- 
berless individuals  or  species,  the  resisting  power  attained  the 
marvelous  degree  that  we  are  constantly  witnessing  in  all 
homoiothermers. 

The  daily  variations  of  the  bodily  temperature  in  homoio- 
thermers is  a  beautiful  example  of  the  law  of  rhythm  evident 
in  the  metabolism.  Hibernation  is  another  such.  While  these 
are  clear  cases,  it  is  without  doubt  true  that,  did  we  but  know 
more  of  the  subject,  a  host  of  examples  of  the  operation  of  this 
law  might  be  instanced. 

We  can  but  touch  on  these  subjects  enough  to  show  that 
they  deserve  an  attention  not  as  yet  bestowed  on  them ;  and  to 
the  thoughtful  it  will  be  evident  that  their  influence  on  prac- 
tical life  might  be  made  very  great  were  they  but  rightly  ap- 


THE  METABOLISM   OF  THE   BODY.  471 

prehended.  In  that  preventive  medicine  of  the  future  to  which 
we  fondly  look  to  advance  the  welfare  of  mankind,  such  consid- 
erations must  largely  enter. 

The  Influence  of  the  Nervous  System  on  Metabolism 

(Nutrition). 

This  subject  is  of  the  utmost  importance,  and  has  not  re- 
ceived the  attention  hitherto,  in  works  on  physiology,  to  which 
we  believe  it  is  entitled,  so  that  we  must  discuss  it  at  some 
length. 

We  may  first  mention  a  number  of  facts  on  which  to  base 
conclusions:  1.  Section  of  the  nerves  of  bones  is  said  to  be  fol- 
lowed by  a  diminution  of  their  constituents,  indicating  an 
alteration  in  their  metabolism.  2.  Section  of  the  nerves  sup- 
plying a  cock's  comb  interferes  with  the  growth  of  that  ap- 
pendage. 3.  Section  of  the  spermatic  nerves  is  followed  by  de- 
generation of  the  testicle.  4.  After  injury  to  a  nerve  or  its 
center  in  the  brain  or  spinal  cord,  certain  affections  of  the 
skin  may  appear  in  regions  corresponding  to  the  distribution 
of  that  nerve :  thus,  herpes  zoster  is  an  eruption  that  follows 
frequently  the  distribution  of  the  intercostal  nerve.  5.  When 
the  motor  cells  of  the  anterior  horn  of  the  spinal  cord  or  cer- 
tain cells  in  the  pons,  medulla,  or  crus  cerebri  are  disordered, 
there  is  a  form  of  muscular  atrophy  which  has  been  termed 
"  active,"  inasmuch  as  the  muscle  does  not  waste  merely,  but 
the  dwindling  is  accompanied  by  proliferation  of  the  muscle 
nuclei.  G.  In  acute  decubitus  bed-sores  form  within  a  few  hours 
or  days  of  the  appearance  of  the  cerebral  or  spinal  lesion,  and 
this  with  every  precaution  to  j)revent  pressure  or  the  other 
conditions  that  favor  the  formation  of  such  sores.  7.  After 
section  of  both  vagi,  death  results  after  a  period,  varying  in 
time,  as  do  also  the  symptoms,  with  the  animal.  In  some  ani- 
mals pneumonia  seems  to  account  for  death,  since  it  is  found 
that,  if  this  disease  be  prevented,  life  may,  at  all  events,  be 
greatly  prolonged.  The  pneumonia  has  been  attributed  to 
I)aralyses  of  the  mu.scles  of  the  larynx,  together  with  loss  of 
sensiliility  of  the  larynx,  trachea,  bronchi,  and  the  lungs,  so 
tliat  the  glottis  is  not  closed  during  deglutition,  and  the  food, 
finding  its  way  into  the  lungs,  has  excited  the  disease  by  irrita- 
tion. The  possibility  of  vaso-motor  changes  is  not  to  bo  over- 
lookerl.  In  birds,  death  may  >je  subscqiKMit  to  pneumonia  or 
to  inanition  froiri  j>;iralysis  of  tlif  o'sopIiaguH,  food  not  being 


472  ANIMAL   PHYSIOLOGY. 

swallowed.  It  is  noticed  that  in  these  creatures  there  is  fatty 
(and  sometimes  other)  degeneration  of  the  heart,  liver,  stomach, 
and  muscles.  8.  Section  of  the  trigeminus  nerve  within  the 
skull  has  led  to  disease  of  the  corresponding  eye.  This  opera- 
tion renders  the  whole  eye  insensible,  so  that  the  presence  of 
offending  bodies  is  not  recognized ;  and  it  has  been  both  as- 
serted and  denied  that  protection  of  the  eye  from  these  pre- 
vents the  destructive  inflammation.  With  the  loss  of  sensi- 
bility there  is  also  vaso-motor  paralysis,  the  intra-ocular  ten- 
sion is  diminished,  and  the  relations  of  the  nutritive  lymph  to 
the  ocular  tissues  are  altered.  But  all  disturbances  of  the  eye 
in  which  there  are  vaso-motor  alterations  are  not  followed  by 
degenerative  changes.  9.  Degeneration  of  the  salivary  glands 
follows  section  of  their  nerves.  10.  After  suture  of  long-di- 
vided nerves,  indolent  ulcers  have  been  known  to  heal  with 
great  rapidity.  This  last  fact  especially  calls  for  explanation. 
It  will  be  observed,  when  one  comes  to  examine  nearly  all  such 
instances  as  those  referred  to  above,  that  they  are  complex. 
Undoubtedly,  in  such  a  case  as  the  trigeminus  or  the  vagi, 
many  factors  contribute  to  the  destructive  issue ;  but  the  fact 
that  many  symptoms  and  lesions  are  concomitants  does  not,  of 
itself,  negative  the  view  that  there  may  be  lesions  directly 
dependent  on  the  absence  of  the  functional  influence  of  nerve- 
fibers.  We  prefer,  however,  to  discuss  the  subject  on  a  broader 
basis,  and  to  found  opinions  on  a  wider  survey  of  the  facts  of 
physiology. 

After  a  little  time  (a  few  hours),  Avhen  the  nerves  of  the  sub- 
maxillary gland  have  been  divided,  a  flow  of  saliva  begins  and 
is  continuous  till  the  secreting  cells  become  altered  in  a  way 
visible  by  the  microscope.  Now,  we  have  learned  that  proto- 
plasm can  discharge  all  its  functions  in  the  lowest  forms  of 
animals  and  in  plants  independently  of  nerves  altogether. 
What,  then,  is  the  explanation  of  this  so-called  "paralytic 
secretion  "  of  saliva  ?  The  evidence  that  the  various  functions 
of  the  body  as  a  whole  are  discharged  as  individual  acts  or 
series  of  acts  correlated  to  other  functions  has  been  abundantly 
shown ;  and,  looking  at  the  matter  closely,  it  must  seem  un- 
reasonable to  suppose  that  this  would  be  the  case  if  there  was 
not  a  close  supervision  by  the  nervous  system  over  even  the 
details  of  the  processes.  We  should  ask  that  the  contrary  be 
proved,  rather  than  that  the  burden  of  proof  should  rest  on  the 
other  side.  Let  us  assume  that  such  is  the  case ;  that  the  entire 
behavior  of  every  cell  of  the  body  is  directly  or  indirectly  con- 


THE  METABOLISM  OF  THE  BODY.  47^ 

trolled  by  the  nervous  system  in  the  higher  animals,  especially 
mammals,  and  ask.  What  facts,  if  any,  are  opposed  to  such  a 
xievr  ?  We  must  supjwse  that  a  secretory  cell  is  one  that  has 
been,  in  the  course  of  evolution,  specialized  for  this  end.  What- 
ever may  have  been  the  case  with  protoplasm  in  its  unspecialized 
form,  it  has  been  shown  that  gland-cells  can  secrete  independ- 
ently of  blood-supply  (pages  321,  416)  w^hen  the  nerves  going  to 
the  gland  are  stimulated.  Now,  if  these  nerves  have  learned,  in 
the  course  of  evolution,  to  secrete,  then  in  order  that  they  shall 
remain  natural  (not  degenerate)  they  must  of  necessity  secrete ; 
which  means  that  they  must  be  the  subject  of  a  chain  of  meta- 
bolic processes,  of  which  the  final  link  only  is  the  expulsion  of 
formed  products.  Too  much  attention  was  at  one  time  directed 
to  the  latter.  It  was  forgotten,  or  rather  perhaps  unknown, 
that  the  so-called  secretion  was  only  the  last  of  st,  long  series  of 
acts  of  the  cell.  True,  when  the  cells  are  left  to  themselves, 
when  no  influences  reach  them  from  the  stimulating  nervous 
centers,  their  metabolism  does  not  at  once  cease.  As  we  view 
it,  they  revert  to  an  original  ancestral  state  when  they  per- 
formed their  work,  lived  their  peculiar  individual  life  as  less 
specialized  forms  wholly  or  partially  independent  of  a  nervous 
system.  But  such  divorced  cells  fail;  they  do  not  produce 
normal  saliva,  their  molecular  condition  goes  wrong  at  once, 
and  this  is  soon  followed  by  departures  visible  by  means  of  the 
microscope.  But  just  as  secretion  is  usually  accompanied  by 
excess  of  blood,  so  most  functional  conditions,  if  not  all,  de- 
mand an  unusual  supply  of  pabulum.  This  is,  however,  no 
more  a  cause  of  the  functional  condition  than  food  is  a  cause 
of  a  man's  working.  It  may  hamper,  if  not  digested  and  assimi- 
lated. It  becomes,  theii,  apparent  that  the  essential  for  metab- 
olism is  a  vital  connection  with  the  dominant  nervous  system. 

It  has  been  objected  that  the  nervous  system  has  a  metab- 
olism of  its  own  independent  of  other  regulative  influences ; 
but  in  this  objection  it  seems  to  be  forgotten  that  the  nervous 
system  is  itself  made  up  of  parts  which  are  related  as  higher 
and  lower,  or  at  all  events  which  intercommunicate  and  ener- 
gize one  another.  We  have  learned  that  one  muscle-cell  has 
power  to  rouse  another  to  activity  when  an  impulse  has  reached 
it  from  a  nervous  center.  Doubtless  this  phenomenon  has 
many  parallels  in  the  body,  and  explains  how  remotely  a  nerv- 
ous center  may  exert  its  power.  It  enables  one  to  understand  to 
some  extent  many  of  those  wonderful  co-ordinations  (obscure 
in  detail)  that  are  constantly  taking  place  in  the  b()(ly.     We 


474  ANIMAL  PHYSIOLOGY. 

think  the  facts  as  they  accumulate  will  more  and  more  show, 
as  has  been  already  urged,  that  the  influence  of  blood-pressure 
on  the  metabolic  (nutritive)  processes  has  been  much  over- 
estimated. They  are  not  essential  but  concomitant  in  the 
highest  anim.als.  Turning  to  the  case  of  muscle  we  find  that 
when  a  skeletal  muscle  is  tetanized  the  essential  chemical  and 
electrical  phenomena  are  to  be  regarded  as  changes  differing  in 
degree  only  from  those  of  the  so-called  resting  state.  There  is 
more  oxygen  used,  more  carbonic  anhydride  excreted,  etc.  The 
change  in  form  seems  to  be  the  least  important  from  a  physio- 
logical point  of  view.  Now,  while  all  this  can  go  on  in  the 
absence  of  blood  or  even  of  oxygen,  it  can  not  take  place  with- 
out nerve  influence  or  something  simulating  it.  Cut  the  nerve 
of  a  muscle,  and  it  undergoes  fatty  degeneration,  and  atrophies. 
True,  this  may  be  deferred,  but  not  indefinitely,  by  the  applica- 
tion of  electricity,  acting  somewhat  like  a  nerve  itself,  and  in- 
ducing the  approximately  normal  series  of  metabolic  changes. 
If,  then,  the  condition  when  not  in  contraction  (rest)  differs 
from  the  latter  in  all  the  essential  metabolic  changes  in  rate  or 
degree  only ;  and  if  the  functional  condition  or  accelerated 
metabolism  is  dependent  on  nerve  influence,  it  seems  reason- 
able to  believe  that  in  the  resting  condition  the  latter  is  not 
withheld. 

Certain  forms  of  paralysis  (e.  g.,  hysterical)  are  not  followed 
by  atrophy.  Why  ?  Because  in  this  form  the  nerve  influence 
is  still  exerted. 

The  recent  investigations  on  the  heart  make  such  views  as 
we  are  urging  clearer  still.  It  is  known  that  section  of  the 
vagi  leads  to  degeneration  of  the  cardiac  structure.  We  now 
know  that  this  nerve  contains  fibers  which  have  a  diverse 
action  on  the  metabolism  of  the  heart,  and  that,  according 
as  the  one  or  the  other  set  is  stimulated,  so  does  the  electri- 
cal condition  vary ;  and  everywhere,  so  far  as  known,  a  differ- 
ence in  electrical  conditions  seems  to  be  associated  with  a 
difference  in  metabolism,  which  may  be  one  of  degree  only, 
perhaps,  in  many  instances — still  a  difference.  The  facts  as 
brought  to  light  by  experimental  stimulation  harmonize  with 
the  facts  of  degeneration  of  the  cardiac  tissue  on  section  of  the 
vagi ;  but  this  is  only  clear  on  the  view  we  are  now  presenting, 
that  the  action  of  the  nervous  system  is  not- only  universal, 
but  that  it  is  constant  j  that  function  is  not  an  isolated  and 
independent  condition  of  an  organ  or  tissue,  but  a  part  of  a 
long  series  of  metabolic  changes.     It  is  true  that  one  or  more 


THE  METABOLISM   OF   THE   BODY.  475 

of  sucli  changes  may  be  arrested,  just  as  all  of  them  may  go 
on  at  a  less  rate,  if  this  actual  outpouring  of  pancreatic  secre- 
tion is  not  constant ;  but  secretion  is  not  summed  up  in  dis- 
charge merely ;  and,  on  the  other  hand,  it  would  seem  that  in 
some  animals  the  granules  of  the  digestive  glands  are  being 
renewed  while  they  are  being  used  up,  in  secreting  cells.  The 
processes  may  be  simultaneous  or  successive.  Nor  do  we  wish 
to  imply  that  the  nervous  system  merely  holds  in  check  or  in 
a  very  general  sense  co-ordinates  processes  that  go  on  unorigi- 
nated  by  it.  We  think  the  facts  warrant  the  view  that  they  are 
in  the  highest  mammals  either  directly  (mostly)  or  indirectly 
originated  by  it,  that  they  would  not  take  place  in  the  absence 
of  this  constant  nervous  influence.  The  facts  of  common  ob- 
servation, as  well  as  the  facts  of  disease,  point  in  the  strongest 
way  to  such  a  conclusion.  Every  one  has  experienced  the  in- 
fluence, on  not  one  but  many  functions  of  the  body,  we  might 
say  the  entire  metabolism,  of  depressing  or  exalting  emotions. 
The  failure  of  appetite  and  loss  of  flesh  and  mental  power  under 
the  influence  of  grief  or  worry,  tell  a  plain  story.  Such  broad 
facts  are  of  infinitely  more  value  in  settling  such  a  question  as 
that  now  discussed  than  any  single  experiment.  The  best  test 
of  any  theory  is  the  extent  to  which  it  will  explain  the  whole 
round  of  facts.  Take  another  instance  of  the  influence  over 
metabolism  of  the  nervous  system. 

Every  athlete  knows  that  he  may  overtrain — i,  e.,  he  may 
use  his  muscles  so  much  as  to  disturb  the  balance  of  his  powers 
somewhere — very  frecj[uently  his  digestion ;  but  often  there 
seems  to  be  a  general  break — the  whole  metabolism  of  the  body 
seems  to  be  out  of  gear.  If  we  assume  a  constant  nervous  influ- 
ence over  the  metabolic  processes,  this  is  comprehensible.  The 
centers  can  produce  only  so  much  of  what  we  may  call  nerv- 
ous force,  using  the  term  in  the  sense  of  directive  power ;  and 
if  this  be  unduly  diverted  to  the  muscles,  other  parts  must 
suffer.     The  same  holds  of  excessive  mental  application. 

On  this  view  also  the  value  of  rest  or  change  of  occupation 
becomes  clear.  The  nervous  centers  are  not  without  some  re- 
semblance to  a  battery ;  at  most,  the  latter  can  generate  only  a 
definite  quantity  of  electricity,  and,  if  a  portion  of  this  be  di- 
verted along  one  conductor,  less  must  remain  to  pass  by  any 
other. 

It  is  of  practical  importance  to  recognize  that  under  great 
excitement  unusual  discharges  from  a  nerve-center  may  lead 
to  unwonted  functional  activity  :  thus,  under  the  stimulus  of 


476  ANIMAL   PHYSIOLOaY. 

the  occasion  a  man  may  in  a  boat-race  originate  muscular  con- 
tractions that  he  could  not  by  the  strongest  efforts  of  his  will 
call  forth  under  other  circumstances.  Such  are  always  dan- 
gerous. We  might  speak  of  a  reserve  or  residual  nerve  force, 
the  expenditure  of  which  results  in  serious  disability.  It  also 
applies  to  mental  and  emotional  effects  as  well  as  muscular, 
and  seems  to  us  to  throw  light  upon  many  of  the  failures  and 
successes  (so  called)  of  life. 

It  seems  that  our  past  views  of  secretion  and  nutrition  have 
been  partial  rather  than  erroneous  in  themselves,  and  it  is  a 
question  whether  it  would  not  be  well  to  substitute  some  other 
terms  for  them,  or  at  least  to  recognize  them  more  clearly  as 
phases  of  a  universal  metabolism.  "  We  appear  to  be  warranted 
in  making  a  wider  generalization.  To  regard  processes  con- 
cerned in  building  up  a  tissue  as  apart  from  those  that  are  rec- 
ognized as  constituting  its  function,  seems,  with  the  knowledge 
we  at  present  possess,  to  be  illogical  and  unwise.  Whether, 
in  the  course  of  evolution,  certain  nerves,  or,  as  seems  more 
likely,  certain  nerve-fibers  in  the  body  of.  nerve-trunks,  have 
become  the  medium  of  impulses  that  are  restricted  to  regulat- 
ing certain  phases  of  metabolism — as,  e.  g.,  expulsion  of  formed 
products  in  gland-cells — is  not,  from  a  general  point  of  view, 
improbable,  and  is  a  fitting  subject  for  further  investigation. 
But  it  will  be  seen  that  we  should  regard  all  nerves  as  "  tro- 
phic "  in  the  wider  sense.  What  is  most  needed,  apparently,  is  a 
more  just  estimation  of  the  relative  parts  played  by  blood  and 
blood-pressure,  and  the  direct  influence  of  the  nervous  system 
on  the  life-work  of  the  cell.  These  views  are  greatly  strength- 
ened by  the  facts,  well  known  to  every  observer  of  disease  in 
the  human  subject.  The  preponderating  development  of  the 
cerebrum  in  man  must  be  taken  into  account  in  the  working 
of  every  organ.  To  have  a  healthy  stomach,  liver,  kidneys, 
etc.,  is  not  enough  ;  for  real  health,  all  the  parts  of  that  great 
complex  of  organs  we  call  the  brain  must  not  only  work,  but 
work  in  concert. 

We  must  regard  the  nervous  centers  as  the  source  of  cease- 
less pulses  that  operate  upon  all  parts,  originating  and  con- 
trolling the  entire  metabolism,  of  which  what  we  term  func- 
tions are  but  certain  phases,  parts  of  a  whole,  but  essential  for 
the  health  or  normal  condition  of  the  tissues.  Against  such  a 
view  we  know  no  facts,  either  of  the  healthy  or  disordered  or- 
ganism. 

Summary  of  Metabolism. — Very  briefly,  and  somewhat  incom- 


THE  METABOLISM  OP  THE  BODY.  477 

pletely,  we  may  sum  up  the  chief  results  of  our  present  knowl- 
edge (and  ignorance)  as  follows : 

Glycogen  is  found  in  the  livers  of  all  vertebrate  and  some 
invertebrate  animals.  The  quantity  varies  with  the  diet,  being 
greatest  with  an  excess  of  carbohydrates. 

It  seems  likely  that  glycogen  is  manufactured  from  the  pro- 
toplasm of  the  liver-cells,  though  it  is  possible  that  the  latter 
may  act  on  substances  contained  in  the  lymph,  and  convert 
them  into  glycogen  which  they  store  up.  The  phenomena  of 
diabetes  melliius  seem  to  indicate  that  vaso-motor  effects  in  the 
liver  are  not  essential  to  the  formation  of  the  excess  of  sugar 
in  that  disease,  which  excess  is  only  one  symptom,  there  being 
frequently  also  a  largely  increased  secretion  of  urea ;  but  inas- 
much as  tlie  nervous  system  is  greatly  deranged  in  this  malady, 
the  symptoms,  etc.,  of  the  disease  as  a  whole  may  be  rather 
regarded  as  showing  how  important  is  the  due  influence  of 
the  nervous  system. 

Glycogen  may  be  regarded  as  stored  material  to  be  convert- 
ed into  sugar,  as  required  by  the  organism  ;  though  the  exact 
use  of  the  sugar  and  the  method  of  its  disposal  are  unknown. 

Fat  is  not  stored  up  in  the  body  as  the  result  of  being 
merely  picked  out  from  the  blood  ready  made  ;  but  is  a  genuine 
product  of  the  metabolism  of  the  tissues,  and  may  be  formed 
from  fatty,  carbohydrate,  or  proteid  food.  This  becomes  es- 
pecially clear  when  the  difference  in  the  fat  of  animals  from 
that  on  which  they  feed  is  considered,  as  well  as  the  direct  re- 
sults of  feeding  experiments,  and  the  nature  of  the  secretion  of 
milk. 

The  liver  seems  be  engaged  in  a  very  varied  round  of  meta- 
bolic processes :  the  manufacture  of  bile,  of  glycogen,  of  urea, 
and  probably  of  many  other  substances,  some  known  and 
others  unknown,  as  chemical  individuals.  Urea  is  in  great 
part  probably  only  appropriated  by  the  kidney-cells  (Amoeba- 
like) from  the  blood  in  which  it  is  found  ready-made ;  though 
it  may  be  that  a  part  is  formed  in  these  cells,  either  from 
bodies  some  steps  on  the  way  toward  urea,  or  out  of  their  pro- 
toplasm, as  fat  seems  to  be  by  the  cells  of  the  mammary  gland. 

The  leucin  (and  tyrosin  ?)  of  the  digestive  canal  sustains 
some  relation  to  the  manufacture  of  urea  by  the  liver,  and 
possibly  by  the  spleen  and  other  organs ;  for  an  animal  diet 
increases  these  products,  and  also  the  urea  excreted.  Creatin, 
one  of  the  products  of  proteid  metabolism,  and  possibly  allied 
bodies,  may  >je  considered  as  in  a  certain  sense  antecedents  of 


478  ANIMAL  PHYSIOLOGY. 

urea :  uric  acid,  however,  does  not  seem  to  be  such,  nor  is  it  to 
be  regarded  as  a  body  that  has  some  of  it  escaped  complete 
oxidation,  but  rather  as  a  result  of  a  distinct  departure  of  the 
metabolism ;  and  there  are  facts  which  seem  to  indicate  that 
the  uric-acid  metabolism  is  the  older,  from  an  evolutionary- 
point  of  view,  and  that  in  mammals,  and  especially  in  man,  as 
the  results  of  certain  errors  there  may  be  a  physiological  (or 
pathological)  reversion.  Hippuric  acid,  as  replacing  uric  acid 
in  the  herbivora,  may  be  regarded  in  a  similar  light. 

Our  knowledge  of  the  metabolism  of  the  spleen,  beyond  its 
relations  to  the  formation  of  blood-cells  and  their  disintegra- 
tion, is  in  the  suggestive  rather  than  the  positive  stage.  It 
seems  highly  probable  that  this  organ  plays  a  very  imj)ortant 
part,  the  exact  nature  of  which  is  as  yet  unknown. 

When  an  animal  starves,  it  may  be  considered  as  feeding  on 
its  own  tissues,  the  more  active  and  important  utilizing  the 
others.  Notwithstanding,  organs  with  a  very  active  metabo- 
lism, as  the  muscles  and  glands,  lose  weight  to  a  large  extent. 
The  presence  of  urea  to  an  amount  not  very  greatly  below  the 
average  in  health,  shows  that  there  is  an  active  proteid  metab- 
olism then  as  at  all  times  in  progress. 

General  experience  and  exact  experiments  prove  that,  while 
an  animal's  diet  may  be  supplied  with  special  regard  to  fatten- 
ing, to  increase  working  power,  or  simply  to  maintain  it  in 
health,  as  evidenced  by  breeding  capacity,  form,  etc.,  in  all  cases 
there  must  be  at  least  a  certain  minimum  quantity  of  each  of 
the  food-stuffs.  No  one  food  can  be  said  to  be  exclusively 
fattening,  heat-forming,  or  muscle-forming. 

A  carbohydrate  diet  tends  to  production  of  fat ;  flesh,  and 
other  proteid  food  to  supply  muscular  energy,  but  the  latter 
also  produces  fat,  and  a  diet  of  flesh  mixed  with  fat  or  gelatin 
will  serve  the  purposes  of  the  economy  better  than  one  contain- 
ing a  very  much  larger  quantity  of  proteid  alone.  Muscular 
energy,  as  is  to  be  inferred  from  the  excreta,  is  not  the  result 
of  nitrogenous  metabolism  alone ;  and  in  arranging  any  diet 
for  man  or  beast  the  race  and  the  individual  must  be  consid- 
ered. Animals  can  not  be  treated  as  machines,  like  engines 
using  similar  quantities  of  fuel ;  though  this  holds  far  more  of 
man  than  the  lower  animals — i.  e.,  the  results  may  be  predicted 
from  the  diet  with  far  less  certainty  in  the  case  of  man  than  of 
other  mammals. 

Food  is  related  to  excreta  in  a  definite  way,  so  that  all  that 
enters  as  food  must  sooner  or  later  appear  as  urea,  salts,  car- 


THE  METABOLISM  OF  THE   BODY.  479 

bonic  anhydride,  water,  etc.  These  are  individually  to  be  re- 
garded as  the  final  links  in  a  long  chain  of  metabolic  processes 
or  rather  a  series  of  these.  Fats  and  carbohydrates  are  repre- 
sented finally  as  carbonic  anhydride  and  water  principally,  pro- 
teids  as  urea. 

Nitrogenous  foods  may  be  regarded  as  accelerating  the 
metabolic  processes  generally  and  proteid  metabolism  in  par- 
ticular, while  fats  have  the  reverse  eifect ;  hence  fat  in  the  diet 
renders  a  less  quantity  of  proteid  sufficient.  Gelatine  seems  to 
act  when  mixed  with  proteid  food  either  like  an  additional 
quantity  of  proteid,  or  possibly  like  fat,  at  all  events  under  such 
circumstances  less  proteid  suffices. 

These  facts  have  a  bearing  not  only  on  health  but  on  econ- 
omy, in  the  expenditure  for  food. 

Salts  hold  a  very  important  place  in  every  diet,  though 
their  exact  influence  is  in  great  part  unknown.  The  heat  of 
the  body  is  the  resultant  of  all  the  metabolic  processes  of  the 
organism,  especially  the  oxidative  ones.  Certain  food-stuffs 
have  greater  potential  capacity  for  heat  formation  than  others ; 
but,  finally,  the  result  depends  on  whether  the  organism  can 
best  utilize  one  or  the  other. 

A  certain  body  temperature,  varying  only  within  narrow 
limits,  is  maintained,  partly  by  regulation  of  the  supply  and 
partly  by  the  regulation  of  the  loss. 

Both  these  are,  in  health,  under  the  direction  of  the  nervous 
system,  and  both  are  co-ordinated  by  the  same.  Loss  is  chiefly 
through  the  skin  and  lungs ;  gain  chiefly  through  the  organs 
of  most  active  metabolism,  as  the  muscles  and  glands. 

Vaso-motor  effects  play  a  great  part  in  the  escape  of  heat. 

Animals  may  be  divided  into  poikilothermers  and  homoio- 
thermers,  or  cold-blooded  and  warm-blooded  animals,  accord- 
ing as  their  body  heat  varies  with  or  is  indejjendent  of  the  ex- 
ternal changes  of  temperature.  All  the  facts  go  to  show  that 
in  mammals  the  processes  of  the  body  (metabolism)  can  con- 
tinue only  witliin  a  slight  range  of  variations  in  temperature, 
tliough  the  upward  limit  is  narrower  than  tlie  downward. 

Upon  the  whole,  the  evidence  justifies  the  conclusion  that 
the  nervous  system  is  concerned  in  all  the  metabolic  processes 
of  the  body  in  mammals  including  man,  and  that,  as  we  descend 
the  scale,  the  dominion  of  the  nervous  system  becomes  less  till 
we  reach  a  point  wlum  protoplasm  goes  through  the  whole 
cycle  of  its  changes  )jy  virtue  of  its  own  propcrtii^s  uninfluenced 
by  any  modification  of  itself  in  the  form  of  a  iKn'vous  system. 


480 


ANIMAL  PHYSIOLOGY. 


THE  SPINAL  CORD.— GENERAL. 

Among  the  higher  vertebrates  the  spinal  cord  is  found  to 
consist  of  nerve-cells,  nerve-fibres,  and  a  delicate  connective  tis- 
sue binding  them  together ;  while  these  different  structures  are 
arranged  in  definite  forms,  so  that  a  cross-section  anywhere  pre- 
sents a  characteristic  appearance,  the  more  important  gangli- 
onic nerve-cells  being  internal  and  forming  a  large  part  of 


Fig.  341.— General  view  of  nervous  system  of  man  (after  Mivart).    1,  cerebrum  ;  2,  cerebel- 
lum ;  3,  upper  part  of  spinal  cord. 

the  gray  matter  of  the  cord.  All  the  various  regions  of  this 
organ  or  series  of  organs  are  connected  with  one  another,  white 
with  white  and  gray  matter,  as  well  as  white  with  gray  sub- 


THE  SPINAL  CORD.— GENERAL. 


481 


stance.     The  cord  may  be  regarded  either  as  an  instrument  for 
the  reception  and  generation  of  impulses  independent  of  the 


Fig.  342.— Transverse  section  of  spinal  cord  of  child  six  mouths  old,  at  middle  of  lumbar 
region,  showing  especially  the  fibers  of  gray  substance.  1  x  20.  (After  (ierlach.)  o,  ante- 
rior columns ;  h,  posterior  columns  ;  c,  lateral  columns  ;  d.  anterior  roots  ;  e,  posterior 
roots  ;  /,  anterior  white  commissure  ;  g,  central  canal  lined  by  epithelial  cells  ;  h,.  con- 
nective-tis.sue  substance  surrounding  it ;  i,  transverse  fibers  of  gray  commissure  in  front, 
and  k.  the  same  behind  central  canal ;  I,  two  veins  cut  across ;  »»,  anterior  cornua  ;  n, 
great  lateral  cell  group  of  anterior  cornua  ;  o.  lesser  anterior  cell  group  (column) ;  p, 
smallest  median  cell  group  ;  7,  posterior  cornua  ;  r,  ascending  fasciculi  in  posterior 
cornua  ;  .v,  substantia  gelatinosa. 

brain  ;  or  as  a  conductor  of  afferent  and  efferent  impulses  des- 
tined for  the  brain  or  originating  in  that  organ.  As  a  matter 
of  fact,  however,  it  is  better  to  bear  in  mind  that  the  cord  and 
brain  constitute  one  organ  or  chain  of  organs,  which,  as  we 
have  learned  from  our  studies  in  development,  are  differentia- 
tions of  one  common  track,  originating  from  the  epiblast. 

While  the  brain  and  the  cord  may  act  independently  to  a 
very  large  extent,  as  may  be  shown  by  experiment,  yet  it  can 
not  be  too  well  borne  in  mind  that  in  the  actual  normal  life  of 
an  animal  such  purely  ind<!i)f;nd('nt  behavior  must  bo  exceed- 
ingly rare.  We  are  constantly  in  danger,  in  studying  a  sub- 
ject, of  making  in  our  minds  isolations  which  do  not  exist  in 
nature.     When  one  accidentally  sits  uj)on  a  sharp  object,  he 

81 


482 


ANIMAL   PHYSIOLOGY. 


rises  suddenly  without  a  special  effort  of  will  power  ;  he  experi- 
ences pain,  and  has  certain  thoughts  about  the  object,  etc. 


Fig.  343.— Group  of  cells  in  connection  with  anterior  roots  of  spinal  nerves,  as  seen  in  trans- 
verse section  of  spinal  cord  of  sheep  (after  Flint  and  Dean).  A,  emergence  of  anterior' 
roots  from  gray  matter  ;  b,  b,  b,  cells  connected  both  with  each  other  and  with  fibers  of 
anterior  roots. 


Now,  in  reality  this  is  very  complex,  though  it  can  be  ana- 
lyzed into  its  factors.  Thus,  afferent  nerves  are  concerned,  the 
spinal  cord  as  a  reflex  center,  efferent  nerves  to  the  muscles 
called  into  action,  the  cord  as  a  conductor  of  impulses  which  re- 
sult in  sensations,  emotions  and  thoughts  referable  to  the  brain  ; 
so  that  if  we  would  grasp  the  state  of  affairs  it  is  of  importance 


THE  SPINAL  CORD.— GENERAL. 


483 


to  so  combine  the  various  processes  in  our  mental  conception 
that  it  shall  in  oui-  minds  form  that  whole  which  corresponds 


Fio.  »14. 


Fro.  345. 


Fio.  344.— Divixion  of  a  HlcndfT  ncrve-flber,  and  commiinioat-lon  of  its  hranches  with  hig^hly 
ramifyintr  i>ro<;"-KWH  of  two  nf-rvr'-cclls  from  spinal  cord  of  ox.     1  x  MiO.     (Aft^T  Clerlach.) 

Fio.  .^1.1.  -Multipolar  jjant^lion  cell  from  ant^^rior  jfray  matter  of  spiiaal  cord  of  ox  (after 
IMUtni).    a,  axiH  cylinder  procewj ;  h,  branched  proceHWH. 


with  nature,  as  we  have  been  insisting  upon  in  tlie  last  chapter. 
Witli  this  admonition,  and  assuming  a  good  knowledge  of  the 


484  ANIMAL   PHYSIOLOGY. 

general  and  minute  anatomy  of  the  spinal  cord,  we  shall  pro- 
ceed to  discuss  its  functions. 


The  Reflex  Functions  of  the  Spinal  Cord. 

The  following  experimental  observations  may  readily  be 
made  by  the  student  himself :  Let  a  decapitated  frog  be  sus- 
pended freely  (from  the  lower  jaw).  It  hangs  motionless  and 
limp  at  first,  but  when  it  recovers  from  the  shock  (abolition  of 
function)  to  the  spinal  cord  produced  by  the  operation,  it  may 
be  shown  that  this  organ  is  functional :  1.  When  a  piece  of 
bibulous  paper  dipped  in  dilute  acid  is  placed  upon  the  thigh, 
the  leg  is  drawn  up  and  wipes  away  the  offending  body,  2.  If 
the  paper  be  placed  on  the  anus,  both  legs  may  be  drawn  up, 
either  successively  or  simultaneously.  3.  If  the  leg  of  one 
side  be  allowed  to  hang  in  the  dilute  acid,  it  will  be  withdrawn. 
4.  If  a  small  piece  of  blotting-paper  dipped  in  the  acid,  be 
placed  on  the  thigh,  and  the  leg  of  that  side  gently  held,  the 
other  may  be  drawn  up  and  remove  the  object. 

It  may  be  noticed  that  in  every  case  a  certain  interval  of 
time  elapses  before  the  result  follows.  Upon  increasing  the 
strength  of  the  acid  very  much  this  interval  is  shortened,  and 
the  number  of  groups  of  muscles  called  into  action  is  increased. 
Again,  the  result  is  not  the  same  in  all  respects  when  the 
nerve  of  the  leg  is  directly  stimulated,  as  when  the  skin  first 
receives  the  impression.  Section  of  the  nerves  of  the  parts 
abolishes  these  effects ;  so  also  does  destruction  of  the  spinal 
cord,  or  the  part  of  it  with  which  the  nerves  of  the  localities 
stimulated  are  connected;  and  more  exact  experiments  show 
that  in  the  absence  of  the  gray  matter  the  section  of  the  pos- 
terior or  anterior  roots  of  the  nerves  also  renders  such  mani- 
festations as  we  have  been  describing  impossible. 

These  experiments  and  others  seem  to  show  that  an  afferent 
nerve,  an  efferent  nerve,  and  one  or  more  central  cells  are 
necessary  for  a  reflex  action ;  that  the  latter  is  only  a  perfectly 
co-ordinated  one  when  the  skin  (end-organs)  and  not  the 
nerve-trunks  are  stimulated ;  that  there  is  a  latent  period  of 
stimulation,  suggesting  a  central  "summation"  of  impulses 
necessary  for  the  effect ;  that  the  reflex  is  not  due  to  the  mere 
passage  of  impulses  from  an  afferent  to  an  efferent  nerve 
through  the  cord,  but  implies  important  processes  in  the  cen- 
tral cells  themselves.  The  latter  is  made  further  evident  from 
the  fact  that  (1)  strychnia  greatly  alters  reflex  action  by  short- 


THE  SPIXAL   CORD.— GENERAL.  485 

ening  the  latent  period  and  extending  the  range  of  muscular 
action,  which,  it  has  been  shown,  is  not  due  to  changes  in  the 
nerves  themselves.  A  very  slight  stimulus  suffices  in  this  in- 
stance to  cause  the  whole  body  of  a  decapitated  frog  to  pass 
into  a  tetanic  spasm.  We  must  suppose  that  the  processes 
usually  confined  to  certain  groups  of  central  cells  have  in  such 
a  case  involved  others,  or  that  the  "  resistance  "  of  the  centers 
of  the  cord  has  been  diminished,  so  that  many  more  cells  are 
now  involved ;  hence  many  more  muscles  called  into  action. 
Normally  there  is  resistance  to  the  passage  of  an  impulse  to  the 
opposite  side  of  the  cord,  as  is  shown  by  the  fact  that  when  a 
slight  stimulus  is  applied  to  the  leg  of  one  side  the  reflex  is 
confined  to  this  member. 

It  is  evident,  then,  that  the  reflex  resulting  is  dependent  on 
(1)  the  location  of  the  stimulus,  (2)  its  intensity  and  duration, 
(3)  its  character,  and  (4)  the  condition  of  the  spinal  cord  at  the 
time.  Occasionally  on  irritating  one  fore-limb  the  opposite 
hind  one  answers  reflexly.  Such  is  a  "  crossed  reflex,"  and  is 
the  more  readily  induced  in  animals  the  natural  gait  of  which 
involves  the  use  of  one  fore-leg  and  the  opposite  hind-limb 
together. 

Reflexes  are  often  spoken  of  as  purposive,  and  suggest  at 
first  intelligence  in  the  cord  ;  but  such  phenomena  are  explained 
readily  enough  without  such  a  strained  assumption. 

Evolution,  Jieredity,  and  the  law  of  habit,  apply  here  as  else- 
where. The  relations  of  an  animal  to  its  environment  must 
necessarily  call  into  play  certain  nervo-muscular  mechanisms, 
which  from  the  law  of  habit  come  to  act  together  when  a 
stimulus  is  applied.  Naturally  those  that  make  for  the  welfare 
of  the  animal  are  such  as  are  most  used  under  the  influence  of 
the  intelligence  of  the  animal — i.  e.,  of  the  domination  of  the 
higher  cerebral  centers,  so  that  when  the  latter  are  removed  it 
is  but  natural  that  the  old  mechanisms  should  be  still  employed. 
Moreover,  the  reflex  movements  are  not  always  beneficial,  as 
when  a  decapitated  snake  coils  itself  around  a  heated  iron 
under  reflex  influence,  which  is  readily  enough  understood  if 
we  remember  the  habit  of  coiling  around  objects,  and  what 
this  involves — viz.,  organized  tendencies. 

Inhibition  of  Reflexes. — It  can  be  shown  in  the  case  of  a  frog 
tliat  still  retains  its  optic  lobes  and  the  parts  of  the  brain  pos- 
terior to  them  that,  when  these  are  stimulated  at  the  same  time 
as  the  leg,  th(5  reflex,  if  it  occurs  at  all,  is  greatly  delayed. 

On  the  other  hand,  in  the  case  of  dogs,  from  which  a  part 


486  ANIMAL   PHYSIOLOGY. 

of  the  cerebral  cortex  lias  been  removed,  tlie  reflexes  are  mncli 
more  prominent  than  before.  Experience  teaches  us  that  the 
acts  of  defecation,  micturition,  erection  of  the  penis,  and  many 
others,  are  susceptible  of  arrest  or  may  be  prevented  entirely 
when  the  usual  stimuli  are  still  active,  by  emotions,  etc. 
"  These  and  numerous  other  facts  tend  to  show  that  the  higher 
centers  of  the  brain  can  control  the  lower ;  and  it  is  not  to  be 
doubted  that  pure  reflexes  during  the  waking  hours  of  the 
.higher  animals,  and  especially  of  man,  are  much  less  numerous 
than  among  the  lower  vertebrates.  The  cord  is  the  servant  of 
the  brain,  and  a  faithful  and  obedient  one,  except  in  cases  of 
disease,  to  some  forms  of  which  we  have  already  referred. 

Certain  recent  experiments  show  in  the  clearest  way  how  the 
conditions  of  the  central  nervous  system,  and  especially  in  the 
first  instance,  the  brain  <ietermines  the  reflex  time  to  which  we 
shall  presently  refer :  thus,  among  other  influences,  music  and 
even  different  airs  greatly  alter  the  reflex-time,  and,  indeed, 
the  whole  character  of  the  act  (tendon-reflex). 

It  is  not  to  be  supposed,  however,  that  the  processes  that 
are  clearly  cerebral,  and  which  m.odify  normal  reflexes  so 
greatly,  are  all  of  the  nature  of  inhibitions,  or  that  they  are 
at  all  fully  understood.  They  are  unquestionably  very  complex 
in  nature,  and  probably  too  intricate  to  be  completely  un- 
raveled. 

Reflex  Time. — One  of  the  most  satisfactory  methods  of  ascer- 
taining the  length  of  time  a  reflex  a,ct  occupies  is  the  follow- 
ing :  Let  an  electric  stimulus  be  applied  to  one  of  the  eyelids, 
whereupon  both  blink.  The  whole  interval,  minus  the  latent 
period  of  the  orbicularis  muscle  and  the  time  occupied  in  the 
transmission  of  the  necessary  nervous  impulses  over  the  nerves 
concerned  (the  fifth  and  facial)  to  and  from  the  centers  involved 
(medulla),  gives  the  duration  of  the  processes  in  the  brain-cells. 
The  whole  period  in  one  instance  was  '0662  seconds,  which,  re- 
duced as  indicated,  gives  '0555  as  the  time  required  for  the 
changes  that  take  place  in  the  brain-cells. 

It  will,  of  course,  be  understood  that  at  best  these  figures 
are  but  an  approximation,  owing  to  several  possible  sources  of 
error ;  also  that,  as  has  been  already  stated,  the  actual  period 
varies  with  the  condition  of  each  subject  at  the  time  of  ex- 
periment, not  to  mention  the  variations  for  individuals  and 
groups  of  animals.  In  the  instance  chosen  the  brain  itself  was 
the  center  involved,  but  the  same  laws  apply  to  the  reflex 
mechanisms  of  the  cord. 


THE  SPINAL  CORD.— GEXERAL.  487 

The  Spixal  Cord  as  a  Conductor  of  Impulses. 

Before  considering  the  results  arrived  at  in  this  connection, 
some  brief  account  of  the  methods  applied  in  the  investigation 
of  the  subject  is  called  for,  to  enable  the  student  to  appreciate 
their  difiiculties  and  possible  fallacies,  as  well  as  such  grounds 
of  certainty  as  there  may  be  for  the  conclusions  reached. 

Three  or  four  methods  of  research  have  been  employed :  1. 
Sections  of  the  spinal  cord  of  varying  extent,  both  unilateral 
and  bilateral.  In  estimating  the  value  to  be  attached  to  the 
symptoms  following,  the  difficulties  in  limiting  the  section,  the 
interference  of  haemorrhage,  the  inevitable  results  of  operative 
shock,  and,  as  in  all  experiments  on  the  nervous  system  of  ani- 
mals, the  danger  of  misinterpreting  the  symptoms,  must  be 
given  due  weight.  2.  Attempts  have  been  made  to  determine 
the  course  and  relations  of  nerve-fibers  by  ascertaining  the 
order  in  which  the  different  portions  of  the  spinal  nerve-fibers 
receive  their  investing  myelin,  those  with  the  longest  course 
being  the  latest  to  be  thus  completed.  This  is  the  method  of 
Flechsig,  who  has  mapped  out  the  cord  into  a  series  of  columns, 
to  be  referred  to  again  presently.  The  method  is  open  to  the 
objection  of  all  anatomical  ones.  It  is  a  remarkable  fact  that, 
by  strictly  physiological  methods  (i.  e.,  ascertaining  the  function 
of  parts),  nervous  tracts  have  been  traced,  which  were  quite 
unsuspected  as  the  result  of  anatomical  investigation  alone. 
Nevertheless,  this  method,  taken  with  others  now  under  con- 
sideration, has  rendered  important  service.  3.  Following  upon 
experimental  sections,  as  well  as  in  consequence  of  certain  dis- 
eases in  the  brain  and  cord,  fibers  have  been  found  to  degenerate 
along  certain  definite  paths,  owing,  it  is  believed,  to  being  cut 
off  from  their  trophic  centers ;  so  that  if,  after  section  of  the 
cord,  there  is  degeneration  of  fibers  downward,  it  is  inferred 
that  the  trophic  cells  lie  above  the  seat  of  degeneration  and 
the  reverse.  This  may  be  called  the  pathological  (Wallerian) 
method,  and  in  conjunction  with  clinical  evidence  has,  in  the 
case  of  man  especially,  been  the  chief  source,  perhaps,  of  our 
knowledge  in  regard  to  the  conducting  paths  in  the  human 
cord ;  though  other  methods,  as  carried  out  in  the  lower  ani- 
mals, have  yielded  results  which  have  been  sujjplementary  and 
corrective ;  and  in  truth  a  variety  of  means  must  be  employed, 
and  the  greatest  caution  observed,  or  the  inferences  drawn  will 
be  partial  if  not  actually  erroneous. 

It  is  to  be  carefully  borne  in  mind  now,  and  when  studying 


488 


ANIMAL   PHYSIOLOGY. 


Fio.  346 


the  brain,  that  a  conducting  path  in  the  nervous  centers  is  not 
synonymous  with  conducting  fibers.     The  cells  themselves  and 

the  neuroglia  probably  are  also 
/,  conductors.     We  shall  now  en- 

/    \  deavor  to   map   out,  as   estab- 

lished by  the  method  of  Flech- 
sig.  Waller,  and  others,  the 
main  fiber  tracts  of  the  spinal 
cord. 

1.  Antero  -  median  Columns 
(columns  of  Tiirck).  These 
probably  decussate  in  the  cerv- 
cial  region,  where  they  are  most 
marked,  constituting  the  direct 
or  uncrossed  pyramidal  tract, 
and  disappear  in  the  lower  dor- 
sal region. 

Secondary  degeneration  en- 
sues in  these  tracts  upon  cer- 
tain brain-lesions,  in  the  motor 
regions. 

2.  Crossed  Pyramidal  Tracts. 
— They  pass  forward  to  form 
part  of  the  anterior  pyramids  of 
the  medulla  after   decussation 

in  their  lower  part.  Similarly  to  the  first,  degeneration  follows 
in  these  tracts  when  there  are  brain-lesions  of  the  motor  area. 
Hence,  both  of  these  constitute  descending  motor  paths. 

3.  Anterior  Fasciculi  (fundamental  or  ground  bundle). — 
They  possibly  connect  the  gray  matter  of  the  cord  with  that  of 
the  medulla. 

4.  Anterior  Radicular  Zones,  in  the  anterior  part  of  the  lat- 
eral column. 

5.  Mixed  Lateral  Columns. — These  and  the  preceding  are 
functionally  similar  to  3.  Neither  3,  4,  nor  5  degenerate,  on 
section  of  the  cord,  from  which  it  is  inferred  that  they  have 
trophic  cells  both  above  and  below. 

6.  Direct  Cerebellar  Tracts. — These  bundles,  passing  by  the 
funiculi  graciles  or  posterior  pyramids  of  the  medulla,  reach 
the  cerebellum  by  its  inferior  peduncles. 

These  fasciculi  enlarge  from  their  site  of  origin  in  the  lum- 
bar cord  upward.  After  section  of  the  cord  they  show  ascend- 
ing degeneration,  so  that  it  seems  probable  that  their  trophic 


Diagrammatic  representation  of 
columns  and  conducting  paths  in  spinal 
cord  in  upper  dorsal  region  (after  Flint 
and  Landois).  AR,  AR,  anterior  roots  of 
spinal  nerves  ;  PR.  PR,  posterior  roots  ; 
A.  columns  of  Tiirck  (antero-median  col- 
umns) ;  B,  anterior  fundamental  fascic- 
ulus ;  C,  columns  of  Goll ;  D,  columns  of 
Burdach  ;  E,  E,  anterior  radiculai  zones ; 
P,  F,  mixed  lateral  columns  ;  G,  G, 
crossed  pyramidal  tracts ;  H,  H,  direct 
cerebellar  fibers. 


THE  SPINAL   CORD.— GENERAL.  489 

cells  are  to  be  referred  to  the  posterior  gray  cornua  of  the  cord, 
which  they  connect  in  all  probability  with  the  cerebellum. 

7.  Columns  of  Burdach  (postero-lateral  columns). — This 
tract  is  connected  with  the  restiform  bodies  and  reaches  the 
cerebellum  by  the  inferior  peduncles.  Secondary  degenera- 
tions do  not  occur  in  these  fasciculi,  so  that  it  seems  likely  that 
they  connect  nerve-cells  at  different  levels  in  the  cord ;  and 
they  may  also  connect  the  posterior  gray  cornua  with  the  cere- 
bellum as  6. 

Columns  of  Ooll  (postero-median  columns). — They  do  not 
extend  beyond  the  lower  dorsal  or  upper  lumbar  region ;  and 
their  fibers  pass  to  the  funiculi  graciles  of  the  medulla.  As- 
cending degeneration  follows  section  of  these  columns. 

The  degenerations  referred  to  above  are  visible  by  the 
microscope,  and  of  the  character  following  section  of  nerves. 
It  is  probable  that  they  are  the  later  stages  of  a  primary  mo- 
lecular derangement  in  consequence  of  interference  with  that 
continuous  functional  connection  between  all  parts  on  which 
what  has  been  called  nutrition,  but  which  we  have  shown  is 
but  a  phase  of  a  complex  metabolism,  depends. 

Decussation. — Sections  of  the  cord,  when  confined  to  one  lat- 
eral half,  are  followed  by  paralysis  on  the  same  side  and  loss  of 
sensation,  confined  chiefly  to  the  opposite  half  of  the  body  be- 
low the  point  of  section.  The  results  of  experiment,  patho- 
logical investigation,  etc.,  have  rendered  it  clear  that — 1.  The 
great  majority  of  the  fibers  passing  between  the  periphery  and 
the  brain  decussate  somewhere  in  the  centers.  2.  Afferent 
fibers  cross  almost  directly  but  also  to  some  extent  along  the 
whole  length  of  the  cord  from  their  point  of  entrance,  the 
decussation  being,  however,  completed  before  the  medulla  is 
passed.  3.  Motor  or  efferent  fibers  decussate  chiefly  in  the 
medulla,  though  crossing  is  continued  some  distance  down  the 
cord,  such  latter  fibers  being  but  a  small  portion  of  the  whole. 
This  fact  is  best  established,  perhaps,  by  noting  the  results  of 
brain-lesions.  With  few  exceptions,  susceptible  of  explanation, 
a  lesion  of  one  side  of  the  cerebrum  is  followed  by  loss  of  motion 
of  the  opposite  side  of  the  body.  These  are  all  central,  well- 
established  truths.  It  is  also  now  pretty  well  determined  that 
voluntary  motor  impulses  descend  by  the  pyramidal  tracts, 
both  the  direct  and  the  crossed.  That  the  posterior  columns  of 
the  cord  are  in  some  way  concerned  with  sensory  impulses 
there  is  no  doubt;  but  when  an  attempt  is  made  to  decide 
details,  great  difficulties  are  encountered.      Experiments  on 


490 


ANIMAL  PHYSIOLOGY. 


animals  are  of  necessity  very  unsatisfactory  in  sncli  a  case, 
from  the  difficulty  experienced  in  ascertaining  their  sensa- 
tions at  any  time,  and  especially  when  disordered. 

Pathological. — A  good  deal  of  stress  has  been  laid  upon  the 
teachings  of  locomotor  ataxia  in  the  human  subject.  The 
symptoms  of  this  disease  are  found  associated  with  lesions  of 
the  posterior  columns  of  the  cord.  The  essential  feature  is  an 
inability  to  co-ordinate  movements,  though  muscular  power 
may  be  unimpaired.  But  such  inco-ordination  is  not  usually 
the  only  symptom;  and,  while  the  disease  seems  usually  to 
begin  in  Burdach's  columns,  the  columns  of  Goll,  the  posterior 
nerve-roots,  and  even  the  cells  of  the  posterior  cornua,  may 
be  involved,  so  that  the  subject  becomes  very  complicated. 
Co-ordination  of  muscular  movements  is  normally  dependent 
upon  certain  afferent  sensory  impulses,  themselves  very  com- 
plex.    It  is  to  be  remembered  also  that  there  are  numberless 


p.m.f. 


Fig.  347. — Diagram  to  illustrate  probable  course  taken  by  fibers  of  nerve-roots  on  entering 

spinal  cord  (Schafer). 


connecting  links  between  the  two  sides  of  the  cord  and  be- 
tween its  different  columns  of  an  anatomical  kind,  not  to  men- 
tion the  possibly  numerous  physiological  (functional)  ones. 

"We  have  stated  above  that  section  of  one  lateral  half  of  the 
cord  is  followed  by  loss  of  sensation  on  the  opposite  side  of  the 
body ;  but  directly  the  contrary  has  been  maintained  by  other 
observers ;  while  still  others  maintain  that  the  effects  are  not 


THE   SPINAL   CORD.— GENERAL. 


491 


confined  to  one  side,  though  most  pronounced  on  the  side  of  the 
section.     The  same  remark  applies  to  motion. 

While  there  is  considerable  agreement  as  to  the  pyramidal 
tracts  of  the  lateral  column,  the  functions  of  the  rest  of  these 
di'V'isions  of  the  cord  are  by  no  means  well  established.  It  is 
possible  that  vasomotor,  respiratory,  and  probably  other  kinds 
of  impulses,  pass  by  portions  of  the  lateral  tracts  other  than 
the  crossed  pyramidal.  When  a  lateral  half  of  the  cord  is 
divided,  the  loss  of  function  is  not  permanent  in  all  instances, 
but  has  been  recovered  from  without  any  regeneration  of  the 
divided  fibers ;  and  even  when  a  section  has  been  made  higher 
up  on  the  opposite  side,  partial  recovery  has  again  followed : 
so  that  it  would  appear  that  impulses  had  pursued  a  zigzag 
course  in  such  cases.  We  do  not  think  that  such  experiments 
show  that  impulses  do  not  usually  follow  a  definite  course,  but 
that  the  resources  of  nature  are  great,  and  that,  when  one  tract 
is  not  available,  another  is  taken. 

It  is  plain  that  impulses  do  not  in  any  case  travel  by  one 
and  the  same  nerve-fiber  throughout  the  cord,  for  the  size  of 
this  organ  does  not  permit  of  such  a  view  being  entertained ; 
at  the  same  time  there  is  a  relation  between  the  size  of  a  cross- 
section  of  the  cord  at  any  one  point  and  the  number  of  nerves 
connected  with  it  at  that  region. 


»— <-^- 1 I I I I I 1 . I 1 1 i_l I 1 1 1 1 1 u2ju» 

I     T   IV    HI    II   I      V     IV  III    II     I     XII  XI   X  IX  VIII  VII  VI  V    IV   III    II    I    VIII  VII  VI  V     IV   III  II     J 

Sacral.        Lumbar.  Dorfdi.  Cervical. 

Fio.  348.— Dla^am  to  illustrate  relative  and  absolute  extent  of  (1)  gray  matter,  (2)  white  col- 
umns in  successive  sectional  areas  of  spinal  cord,  and  (3)  sectional  areas  of  several  nerve- 
roots  entering  cord.  .S'fi,  nerve-root") ;  AC,  LC,  PC,  anterior,  lateral,  posterior  columns  ; 
Or,  gray  matter  (after  Schiifer,  Ludwig,  and  Woroschlloff ). 


We  may  attempt  to  trace  the  paths  of  impulses  in  the  cord 
somewhat  as  follows :  1.  Volitional  impulses  decussate  chiefly 
in  the  medulla  (oblongata,  but  also,  to  some  extent,  throughout 
the  whole  h-ngth  of  the  spinal  cord.  They  travel  in  the  lateral 
columns  (crossed  pyramidal  tracts  chiefly,  if  not  exclusively), 
and  eventually  reach  the  anterior  roots  of  the  nerves  through 
the  anterior  gray  cornua,  passing  to  them,  possibly,  by  the  ante- 


492 


ANIMAL   PHYSIOLOGY. 


rior  columns.  From  the  cells  of  the  anterior  cormia,  impulses 
travel  by  the  anterior  nerve-roots  to  the  motor  nerves,  by 
which  connection  is  made  with  the  muscles.  2.  Sensory  im- 
pulses enter  the  cord  from  the  afferent  nerve-fibers  by  the  pos- 
terior nerve-roots,  passing  probably  by  the  posterior  columns  to 
the  posterior  cornua,  thence  to  the  lateral  columns,  decussation 
being  largely  immediate  though  not  completed  for  some  dis- 
tance up  the  cord. 


if        3' 4  25  6'       6  524  3        f 


LOWER  LIMIT  OF 
MEDULLA 


Fig.  349.— Diagram  showing  course  of  fibers  in  spinal  cord  (after  Ranney).  1, 1',  direct  pyrami- 
dal bundles  ;  2,  2',  crossed  pyramidal  bundles,  decussating  in  medulla  ;  3,  3',  direct 
cerebellar  fibers  ;  4,  4',  fibers  related  to  "  muscular  sense,"  decussating  in  medulla  ;  5,  £', 
and  6,  6',  fibers  related  to  the  appreciation  of  touch,  pain,  and  temperature.  The  motor 
bundles  have  a  dot  upon  them  to  represent  the  motor  cells  of  the  cord  (anterior  horn). 
Note  that  the  motor  fibers  escape  from  the  anterior  nerve-root  (a.  r.),  and  that  the  sensory 
bundles  enter  at  the  posterior  nerve-root  {p.  r.),  which  has  a  ganglion  (g)  upon  it. 


It  would  seem  that  the  lateral  columns  are  the  great  high- 
ways of  impulses ;  though  in  all  instances  it  is  likely  that  the 
gray  matter  of  the  cord  plays  an  important  part  in  modify- 
ing them  before  they  reach  their  destination.     Some  observers 


THE  SPINAL   CORD.— GENERAL.  493 

believe  that  sensory  impulses  giving  rise  to  pain  travel  by  the 
gray  matter  of  the  cord  almost  exclusively.  It  would  be  easy 
to  lay  out  the  paths  of  impulses  in  a  more  definite  and  dog- 
matic manner ;  but  the  evidence  does  not  seem  to  warrant  it, 
and  it  is  better  to  avoid  making  statements  that  may  require 
serious  modification,  to  say  the  least,  in  a  few  months.  The 
prominent  principle  to  bear  in  mind  seems  to  be  that  while 
there  are  tracts  in  the  cord  of  the  animals  that  have  been  exam- 
ined and  probably  of  all  that  have  well-formed  spinal  cords, 
along  which  impulses  travel  more  frequently  and  readily  than 
along  others,  it  is  equally  true  that  these  paths  are  not  invaria- 
ble, nor  are  they  precisely  the  same  for  all  groups  of  animals. 
The  cord  can  not  be  considered  independently  of  the  brain ;  and 
there  can  be  no  doubt  that  the  paths  of  impulses  in  the  former 
are  related  to  the  constitution,  anatomical  and  physiological,  of 
the  latter.  It  is  still  a  matter  of  dispute  whether  the  cord  is 
itself  irritable  to  a  stimulus.  As  a  whole  it  is  without  doubt ; 
as  also  the  white  matter  by  itself.  The  gray  matter  is  certainly 
conducting,  but  whether  irritable  or  not  is  still  doubtful.  Why 
the  sensibility  of  the  side  of  the  body  on  which  one  lateral  half 
of  the  cord  has  been  divided  should  be  increased  (hypersesthe- 
sia),  is  also  undetermined.  Possibly  it  is  due  to  a  temporary 
disturbance  of  nutrition,  or  the  removal  of  certain  usual  inhibi- 
tory influences  from  above,  either  in  the  cord  or  brain. 

The  Automatic  Functions  of  the  Spinal  Cord. 

Reference  has  been  already  made  to  the  fact  that  when  por- 
tions of  a  mammal's  cerebrum  are  removed  the  reflexes  of  the 
cord  become  more  pronounced,  owing  apparently  to  the  removal 
of  influences  operating  on  the  cord  from  higher  centers. 

When  the  cord  itself  is  completely  divided  across,  it  often 
happens  (in  the  dog,  for  example)  that  there  are  rhythmic 
movements  of  the  posterior  extremities — i.  e.,  when  the  animal 
has  recovered  from  the  shock  of  the  operation — tliat  part  of  the 
cord  now  independent  of  the  rest  and  of  the  brain  seems  to 
manifest  an  unusual  automatism.  The  question,  however,  may 
be  raised  as  to  whether  this  is  a  Y^urely  automatic  effect,  or  the 
result  of  reflex  action.  But,  whichever  view  be  entertained, 
these  X)henomena  certainly  teach  the  dependence  of  one  part 
upon  another  in  the  normal  animal,  and  should  make  one  cau- 
tious in  ilrawing  conclusions  from  any  kind  of  experiment,  in 
regard  to  tlie  normal  functions.     As  we  have  often  urged  in 


494  ANIMAL   PHYSIOLOGY. 

the  foregoing  chapters,  what  a  part  may  under  certain  circum- 
stances manifest,  and  what  its  behavior  may  be  as  usually 
placed  in  its  proper  relations  in  the  body,  are  entirely  different, 
or  at  least  may  be.  When  one  leg  is  laid  over  the  other  and  a 
sharp  blow  struck  upon  the  patella  tendon,  the  leg  is  jerked  up 
in  obedience  to  muscular  contraction.  It  is  not  a  little  difficult 
to  determine  whether  this  result  is  due  to  direct  stimulation  of 
the  muscle  or  to  reflex  action,  the  first  link  in  the  chain  of 
events  necessary  to  call  it  forth  originating  in  the  tendon; 
hence  the  term  tendon-reflex.  But  at  present  it  is  safer  to 
speak  of  it  as  the  "  knee-jerk,"  or  the  "  tendon-phenomenon." 
It  disappears,  however,  when  the  spinal  cord  is  destroyed  or  is 
diseased,  as  in  locomotor  ataxia,  or  when  the  nerves  of  the 
muscles  or  the  posterior  nerve-roots  are  divided,  showing  that 
the  integrity  of  the  center,  the  nerves,  and  the  muscles  are  all 
essential.  There  are  normally  many  such  phenomena  (reflexes) 
besides  the  "knee-jerk." 

Another  question  very  difficult  to  decide  is  that  relating  to 
the  usual  condition  of  the  muscles  of  the  living  animal.  It  is 
generally  admitted  that  the  muscles  of  the  body  are  all  in  a 
somewhat  stretched  condition,  but  it  is  not  so  clear  whether 
the  skeletal  muscles  are  under  a  constant  tonic  influence  like 
those  of  the  blood-vessels.  It  is  certain  that,  when  the  nerves 
going  to  a  set  of  muscles  are  cut,  when  even  the  posterior  roots 
of  the  nerves  related  to  the  part  involved  are  divided  or  the 
spinal  cord  destroyed,  there  is  an  unusual  flaccidity  of  the 
limb  involved.  But  the  natural  condition  may  be,  it  has  been 
suggested,  the  result  of  reflex  action.  The  subject  is  probably 
more  complex  than  it  has  hitherto  been  considered. 

The  facts  of  such  a  case — those  of  the  tendon-phenomenon 
and  similar  ones — would  be  better  understood  if  the  spinal 
cord,  the  nerves,  and  the  muscles  associated  with  them,  were 
regarded  as  parts  of  a  whole  so  connected  in  their  functions 
that  severance  of  any  one  of  them  leads  to  disorder  of  the  rest. 
That  the  cells  of  the  cord  are  constantly  exercising  an  influence 
through  the  nerves  on  the  muscles,  while  they  in  turn  do  not 
lead  an  independent  existence,  but  are  as  constantly  influenced 
by  afferent  impulses,  and  that  one  of  the  results  is  the  condi- 
tion of  the  muscles  referred  to,  is,  we  are  convinced,  the  case. 
To  say  that  it  is  either  entirely  automatic  or  purely  reflex,  or 
that  the  whole  of  the  facts  would  be  covered  even  by  an 3^  com- 
bination of  these  two  processes,  would  probably  be  unjustifi- 
able.   The  influence  of  the  centers  over  the  metabolism  of  parts 


THE  SPINAL  CORD.— GENERAL.  495 

is  both  constant  and  essential  to  their  well-being ;  and  in  such 
a  case  as  that  now  considered  it  may  be  that  a  certain  degree 
of  tonus  is  normal  to  a  healthy  muscle  in  its  natural  surround- 
ings in  the  body. 

There  is  now  considerable  evidence  in  favor  of  placing  cer- 
tain centers  presiding  over  the  lower  functions,  as  micturition, 
defecation,  erection  of  penis,  etc.,  in  the  spinal  cord  of  mam- 
mals, especially  its  lower  part — which  centers,  if  they  be  not 
automatic,  are  not  reflex  in  the  usual  sense ;  but  their  considera- 
tion is  better  attempted  in  connection  with  the  treatment  of 
the  physiology  of  the  parts  over  which  they  preside. 

Special  Considerations. 

Comparative. — Among  invertebrates  there  is,  of  course,  no 
spinal  cord,  but  each  segment  of  the  animal  is  enervated  by  a 
special  ganglion  (or  ganglia)  with  associated  nerves.  Never- 
theless, these  are  all  so  connected  that  there  is  a  co-ordination, 
though  not  so  pronounced  as  in  the  vertebrate,  in  which  the 
actual  structural  bonds  are  infinitely  more  numerous,  and  the 
functional  ones  still  more  so.  From  this  result  possibilities  to 
the  vertebrate  unknown  to  lower  forms ;  at  the  same  time,  in- 
dependent life  and  action  of  parts  are  necessarily  much  greater 
among  invertebrates,  as  evidenced  especially  by  the  renewal  of 
the  whole  animal  from  a  single  segment  in  many  groups,  as  in 
certain  divisions  of  worms,  etc. 

It  also  follows  from  the  same  facts  that  a  vertebrated  ani- 
mal must  suffer  far  more  from  injury,  in  consequence  of  this 
greater  dependence  of  one  jjart  on  another ;  a  thousand  things 
may  disturb  that  balance  on  which  its  well-being,  indeed,  its 
very  life  hangs.  It  is  noticeable,  moreover,  that,  as  animals 
occupy  a  higher  place  in  the  organic  scale,  their  nervous  sys- 
tem becomes  more  concentrated;  ganglia  seem  to  have  been 
fused  together,  and  that  extreme  massing  seen  in  the  spinal 
cord  and  brain  of  vertebrates  is  foreshadowed.  In  the  chapters 
on  the  brain  numerous  illustrations  of  the  nervous  system  in 
lower  forms  will  be  found. 

The  fact  that  the  brain  and  cord  arise  from  the  same  germ 
layer,  and  up  to  a  certain  point  are  developed  almost  precisely 
alike,  is  full  of  significance  for  physiology  as  well  as  morphol- 
ogy. That  original  deep-lying  connection  is  never  lost,  tliough 
functional  differentiation  keeps  j)ace  with  later  morphological 
differentiation.     But  even  among  vertebrates  the  spinal  cord 


496  ANIMAL   PHYSIOLOGY, 

shows  a  complexity  gradually  increasing  with  ascent  in  the 
organic  series.  In  the  lowest  of  the  fishes  or  vertebrates  {Am- 
loliioxus  lanceolatus)  the  creature  possesses  a  spinal  cord  only 
and  no  brain,  so  that  an  opportunity  is  afforded  of  witness- 
ing how  an  animal  deports  itself  in  the  absence  of  those  direct- 
ive functions,  dependent  on  the  existence  of  higher  cerebral 
centers.  The  Lancelet  spends  a  great  part  of  its  life  buried 
in  mud  or  sand  on  the  bottom  of  the  ocean,  and  its  existence  is 
very  similar  to  that  of  an  invertebrate,  though,  of  course,  the 
dependence  of  parts  on  each  other  is  somewhat  greater. 

Evolution. — According  to  the  general  law  of  habit  and  in- 
heritance, we  should  suppose  that  at  birth  each  group  of  ani- 
mals would  manifest  those  reflex  and  other  functions  of  the 
cord  which  were  peculiar  to  its  ancestors.  Observation  and 
experiment  both  show  that  reflexes,  etc.,  are  hereditary ;  that 
they  tend  to  become  more  and  more  so  with  each  generation ; 
and  at  the  same  time  that  habit  or  exercise  is  essential  for  their 
perfect  development.  They  stand,  in  fact,  in  the  same  relation 
as  instincts,  which  are  closely  connected  with  them.  Like  the 
latter,  they  may  be  modified  by  way  of  increase  or  diminution 
and  otherwise.  To  illustrate,  it  can  not  be  doubted  that  gallop- 
ing is  the  natural  gait  of  horses,  as  shown  by  the  tendency  of 
even  good  trotters  to  "break"  or  pass  into  a  gallop;  but  it  is 
equally  well  known  that  famous  trotters  breed  trotters.  In 
other  words,  an  acquired  gait  becomes  organized  in  the  nervous 
system  (especially)  of  the  animal,  and  is  transmitted  with  more 
and  more  fixity  and  certainty  with  the  lapse  of  time.  But  all 
experience  goes  to  show  that  walking,  running,  or  any  of  the 
movements  of  animals  are,  when  fully  formed  as  habit-reflexes, 
dependent  for  their  initiation  on  the  will  in  most  but  not  all 
instances,  and  require  for  their  execution  certain  combinations 
of  sensory  and  other  afferent  impulses,  and  the  integrity  of  a 
vast  complex  of  nervous  connections  in  the  spinal  cord. 

It  is  well  known  that  one  in  a  period  of  absent-mindedness 
will  walk  into  a  building  to  which  he  was  accustomed  to  go 
years  before,  though  not  of  late,  showing  plainly  that  volition 
was  not  momentarily  required  for  the  act  of  walking  and  all  else 
that  is  involved  in  the  above  behavior.  It  suggests  that  certain 
nervous  and  muscular  connections  have  been  formed,  function- 
ally at  least.  Plainly,  then,  we  should  not  expect  each  indi- 
vidual man's  spinal  cord  to  be  the  same,  but  that  the  series  of 
mechanisms  of  which  every  spinal  cord  is  made  up  should  differ 
with  experience ;  and  if  this  holds  for  individuals,  how  much 


THE  SPINAL  CORD.— GENERAL.  497 

more  must  it  be  true  of  different  groups  of  animals,  the  habits 
of  which  differ  so  widely !  Experiment  has  proved  this  also  so 
far  as  it  has  gone ;  hence  the  great  danger  of  laying  down  laws 
for  the  spinal  cord  from  the  investigation  of  one  animal  or 
even  one  group.  Recent  investigations  have  shown  that,  in 
persons  crippled  from  birth,  or  for  long  periods,  reflexes  which 
had  never  been  properly  established  may,  as  the  result  of  opera- 
tive procedure,  become  possible  through  training.  It  has  also 
been  shown,  both  by  experiment  and  clinical  experience  of  the 
kind  referred  to,  that  when  certain  reflexes  are  imperfectly  de- 
veloped others  are  also  defective,  again  impressing  the  im- 
portance of  that  balance  of  development  which  is  essential  to 
health  or  the  normal  condition  of  an  animal.  This  subject  is 
very  wide,  of  great  practical  importance,  and  deserves  consider- 
ation beyond  what  our  limits  of  space  will  allow. 

All  the  facts  go  to  show  that  the  cord  is  made  up  of  nervous 
mechanisms — if  we  may  so  speak — which  are  naturally  associ- 
ated, both  structurally  and  functionally,  with  certain  nerves 
and  muscles ;  these,  like  the  paths  which  impulses  take  to  and 
from  the  brain,  though  usual,  are  not  absolutely  fixed,  though 
more  so  as  reflex  than  conducting  paths,  while  they  are  con- 
stantly liable  to  be  modified  in  action  by  the  condition  of 
neighboring  groups  of  mechanisms,  etc. 

We  have  said  less  about  the  gray  matter  of  the  cord  as  a 
conductor  than  its  importance  perhaps  deserves.  It  is  believed 
by  maily  that  impulses  which  give  rise  to  sensations  of  pain 
always  travel  by  the  gray  matter ;  and  there  is  not  a  little  evi- 
dence to  show  that,  Avhen  none  of  the  white  columns  are  avail- 
able owing  to  operative  procedure,  disease,  or  other  disabling 
cau.se,  the  gray  matter  will  conduct  impulses  that  usually  pro- 
ceed by  other  tracts. 

Synoptical — The  spinal  cord  is  composed  of  large  ganglionic 
nerve-cells,  fibers,  and  connecting  neuroglia.  Functionally  it 
is  a  conductor,  the  seat  of  certain  automatic  centers  and  of 
reflex  mechanisms.  Probably  in  every  case  the  one  function  is 
to  a  certain  extent  associated  with  the  other — i.  e.,  when  the 
cord  acts  reflexly  it  is  also  a  conductor,  and  the  cells  concerned 
are  so  readily  excited  to  certain  discharges  of  nervous  energy 
that  automaticity  is  suggested,  and  .so  in  otlnu"  instances :  thus, 
in  the  case  of  automaticity,  reflex  influence  or  afferent  impulses 
are  with  difficulty  entirely  excluded  from  consideration. 

Tlie  great  majority  of  conducting  fillers  seem  to  cross  either 
in  the  cord  itself  or  in  the  medulla  oblongata.  The  conducting 
82 


498  ANIMAL  PHYSIOLOGY. 

paths  that  have  been  shown  by  pathological  and  clinical  inves- 
tigation to  be  best  marked  out  in  the  spinal  cord  are  those  for 
voluntary  motor  impulses.  So  far  as  the  functions  of  the  hu- 
man organ  are  concerned,  clinical  and  pathological  facts  have 
thrown  the  greatest  amount  of  direct  light  on  the  subject ;  but 
the  inferences  thus  drawn  have  been  modified  and  supple- 
mented by  the  results  of  experiments  on  certain  other  mam- 
mals. 

It  is  especially  important  to  bear  in  mind  that,  while  certain 
conducting  paths  are  usual,  they  are  not  invariable;  in  like 
manner,  reflex  impulses  may  not  be  confined  to  usual  groups  of 
cells,  but  may  extend  widely,  and  so  bring  into  action  a  large 
number  of  muscles.  The  resulting  reflex  in  any  case  is  depend- 
ent on  the  character,  intensity,  and  location  of  the  stimulus, 
and  especially  on  the  condition  of  the  central  cells  involved. 
In  the  whole  functional  life  of  the  cord  the  influence  of  higher 
center^  in  the  organ  itself  and  especially  in  the  brain  is  to  be 
considered.  The  cord  is  rather  a  group  of  organs  than  a  single 
one. 

THE  BRAIN. 

The  methods  of  investigating  the  functions  of  the  brain  are 
analogous  to  those  employed  for  the  cord,  and  may  be  classed 
as  physiological  proper  and  pathological,  though,  as  a  matter 
of  fact,  neither  one  nor  the  other  is  now  considered  as  reliable 
when  taken  alone.  With  the  pathological  is  generally  in- 
cluded the  clinical  method ;  and  the  conclusions  thus  derived, 
are  corrected  and  supplemented  by  the  results  obtained  by  sec- 
tion, removal,  or  other  operative  procedure  afi^ecting  parts  of 
the  brain.  The  difficulties  are  still  greater  than  in  the  case  of 
the  cord,  on  account  of  the  extreme  complexity  of  the  organ, 
especially  in  the  higher  mammals  and  man. 

At  the  outset  we  may  remark  that  the  whole  subject  will 
be  studied  more  profitably  if  it  be  borne  in  mind  that — 1.  The 
brain  is  rather  a  collection  of  organs,  bound  together  by  the 
closest  anatomical  and  physiological  ties  than  a  single  one ;  in 
consequence  of  which  it  is  quite  impossible  to  understand  the 
normal  function  of  one  part  without  constantly  bearing  in 
mind  this  relationship.  This  aspect  of  the  subject  has  not  re- 
ceived the  attention  it  deserves.  No  one  regards  the  aliment- 
ary tract  as  a  single  organ ;  but  it  is  likely  that  the  dependence 
functionally  of  one  part  of  the  digestive  canal  upon  another 


THE    BRAIN.  499 

is  not  more  intimate  than  that  established  in  that  great  collec- 
tion of  organs  crowded  together  and  making  up  the  brain.  2. 
Since  the  relative  size,  position,  and  anatomical  connections  of 
the  parts  that  make  up  the  brain  are  different  in  diiferent 
groups  of  animals,  not  to  speak  of  the  fact  that  the  functions 
of  any  part  of  the  brain  of  an  animal,  like  that  of  its  spinal 
cord,  already  alluded  to,  must  depend  in  great  part  upon  its 
own  and  its  inherited  ancestral  experiences,  it  follows  that  the 
greatest  caution  must  be  exercised  in  applying  conclusions 
true  of  one  group  of  animals  to  another.  As  we  shall  point 
out,  the  neglect  of  this  precaution  has  led  to  needless  contro- 
versy and  much  misunderstanding.  3.  It  follows,  from  what 
has  been  referred  to  in  1  above,  that  conclusions  based  upon  the 
behavior  of  an  animal  after  section  or  removal  of  a  part  of  the 
brain  must  be,  until  at  least  corrected  by  other  facts,  received 
with  some  hesitation.  4.  It  also  might  be  inferred  from  1  that 
it  is  desirable  to  study  the  simpler  forms  of  brain  found  in  the 
lower  vertebrates,  in  order  to  prepare  for  the  more  elaborate 
development  of  the  encephalon  in  the  higher  mammals  and  in 
man.  5.  The  embryological  development  of  the  organ  also 
throws  much  light  upon  the  whole  subject. 

The  student  will  see  from  these  remarks  that  a  sound  knowl- 
edge of  the  anatomy  of  the  brain  and  its  connections  is  indis- 
pensah)le  for  a  just  appreciation  of  its  physiology;  nor  must 
such  knowledge  be  confined  to  the  human  or  any  other  single 
form  of  the  organ.  There  is  only  one  way  by  which  this  can 
be  attained :  dissection,  with  the  help  of  plates  and  descriptions. 
The  latter  alone  frequently  impart  ideas  that  are  quite  errone- 
ous, though  they  serve  an  especially  good  purpose  in  helping  to 
fix  the  pictures  of  the  natural  objects,  and  in  rcAdving  them 
when  they  have  become  dim. 

It  is  neither  difficult  to  obtain  nor  to  dissect  the  brain  of  the 
fish,  frog,  Ijird,  etc.  Valuable  material  may  be  saved  and  the 
subject  ap[>roached  profitably,  if,  prior  to  the  dissection  of  a  hu- 
man brain,  a  few  specimens  from  some  group  or  groups  of  the 
domestic  animals  be  examined.  However  useful  artificial  brain 
preparations  may  be,  they  are  so  far  from  nature  in  color,  con- 
sistence, and  many  other  properties,  that,  taken  alone,  they  cer- 
tainly may  serve  greatly  to  mislead ;  and  we  hope  the  student 
will  allow  us  to  urge  ujjon  him  the  methods  above  suggested 
for  gfttirig  n-al  lasting  knowloflgc;.  Tlie  figures  given  below 
may  prove  helpful  when  supplomeiiterl  as  we  advise. 

The  great  difference  in  total  size,  and  in  the  relative  propor- 


500  ANIMAL   PHYSIOLOGY. 

tion,  situation,  etc.,  of  parts,  will,  however,  be  obvious,  from 
the  figures  themselves ;  and  as  we  have  already  pointed  out 
more  than  once,  the  preponderance  of  the  cerebrum  in  man 
must  ever  be  borne  in  mind  in  the  consideration  of  his  entire 
organization,  whether  physical,  mental,  or  moral ;  or,  to  put 
the  matter  otherwise,  all  man's  functions  are  the  better  under- 
stood by  the  remembrance  of  this  one  fact,  which  will  be  at 
once  illustrated  when  we  consider  the  result  of  removal  of  the 
cerebrum  in  animals. 

Animals  deprived  of  the  Cerebrum. 

The  cerebrum  may  be  readily  removed  from  a  frog,  without 
producing  either  severe  prolonged  shock  or  any  considerable 
lisemorrhage.  Such  an  animal  remains  motionless,  unless  when 
stimulated,  though  in  a  somewhat  different  position  from  that 
of  a  frog  having  only  its  spinal  cord.  It  can,  however, 
crawl,  leap,  swim,  balance  itself  on  an  inclined  plane,  and  when 
leaping  avoid  obstacles.  One  looking  at  such  an  animal  per- 
forming these  various  acts  would  scarcely  suspect  that  any- 
thing was  the  matter  with  it,  so  perfectly  executed  are  its 
movements.  We  are  forced  to  conclude,  from  its  remaining 
quiet,  except  when  aroused  by  a  stimulus,  that  its  volition  is 
lost ;  but,  apart  from  that,  and  the  fact  that  it  evidently  does 
not  see  as  well  as  before,  it  appears  to  be  normal.  It  has  no 
intelligent  directive  power  over  its  movements.  It  remains, 
therefore,  to  explain  how  it  is  that  they  are  so  much  more 
complete,  so  much  better  co-ordinated  in  the  entire  animal  than 
when  only  the  spinal  cord  is  left.  It  seems  to  be  legitimate  to 
infer  that  the  other  parts  of  the  brain  contain  the  nervous 
machinery  for  this  work,  which  is  usually  stimulated  to  action 
by  the  will,  but  which  an  external  stimulus  may  simulate.  All 
the  connections,  structural  and  functional,  are  present,  except 
those  on  which  successful  volition  depends.  The  frog  with  the 
cord  only,  sinks  at  once  Avhen  thrown  into  water ;  when  gently 
placed  on  its  back,  it  may  and  probably  will  remain  in  that 
position,  without  an  attempt  at  recovery.  There  is,  in  fact, 
very  limited  power  of  co-ordination. 

Removal  of  the  cerebral  lobes  in  the  bird  is  more  likely  to 
be  attended  with  difficulties,  and  conclusions  must  be  drawn 
with  greater  caution. 

But  a  pigeon  may  be  kept  alive  after  such  an  operation  for 
months.     It  can  stand,  balancing  on  one  leg ;  recover  its  post- 


THE   BRAIN.  '  501 

tion  "when  placed  on  its  side;  fly  when  thrown  into  the  air; 
it  will  even  preen  its  feathers,  pick  up  food,  and  drink  water. 
Its  movements  are  such  as  might  be  those  of  a  stupid,  drowsy, 
or  probably  intoxicated  bird ;  but  it  is  plainly  endowed  with 
vision,  thougli  not  as  good  as  before.  But  spontaneous  move- 
ments are  absent,  and  the  pecking  at  food,  etc.,  must  be  consid- 
ered as  associated  reflexes,  and  as  such  are  very  interesting,  in 
that  they  show  how  machine-like,  after  all,  many  of  the  appar- 
ently volitional  acts  of  animals  really  are.  In  a  mammal  so 
great  is  the  shock,  etc.,  resulting  from  the  operative  procedure, 
that  the  actual  functions  of  the  remaining  parts  of  the  brain, 
when  the  cerebral  convolutions  are  removed,  are  greatly  ob- 
scui-ed ;  nevertheless,  little  doubt  is  left  on  the  mind  that  homol- 
ogous parts  discharge  analogous  functions.  It  can  walk,  run, 
leap,  right  itself  when  placed  in  an  unnatural  position,  eat  when 
food  is  placed  in  its  mouth,  and  avoid  obstacles  in  its  path, 
though  not  perfectly.  Yet  it  remains  motionless  unless  stimu- 
lated ;  all  objects  before  its  eyes  impress  it  alike  if  at  all.  The 
animal  evidently  has  neither  volition  nor  intelligence.  Now,  if 
any  of  the  parts  between  the  cerebrum  and  the  medulla  be 
removed,  the  creature  shows  lessened  co-ordinating  power  ;  so 
that  the  inference,  that  these  various  parts  are  essential  consti- 
tuents of  a  complex  mechanism,  all  the  components  of  which 
are  'necessary  to  the  highest  forms  of  muscular  co-ordination 
and  probably  other  functions,  is  unavoidable. 

There  are  all  degrees  of  consciousness,  and  it  is  quite  impos- 
sible to  determine  the  extent  to  which  this  is  interfered  with 
in  animals  treated  as  described.  While  there  can  be  no  doubt 
that  for  the  possession  of  the  higher  forms  of  consciousness  (as 
for  the  perfection  of  all  visual  and  other  sensory  processes)  the 
cerebrum  is  necessary.  It  would,  however,  be  very  hazardous 
to  state  that,  apart  from  this  part  of  the  brain,  consciousness 
did  not  exist.  When  the  whole  encephalon  is  removed,  the 
spinal  cord  alone  remaining,  it  would  not  be  legitimate  to  in- 
fer consciousness  in  the  sense  in  which  that  word  is  usually 
implied  ;  at  the  same  time,  in  the  intact  vertebrate,  we  may 
believe  that  consciousness  is  in  some  sense,  at  least  re- 
lated in  indefinable  ways  to  all  the  vital  processes,  if  not 
their  actual  resultant  ;  inasmuch  as,  either  directly  or  indi- 
rectly, the  nervous  system  in  all  its  i)arts  is  functionally  con- 
nected, and  influences  and  is  itscjlf  influ(!nced  by  every  cell  in 
the  body. 

Since  we  are  dealing  with  co-ordinated  movements,  wo  may 


502  ANIMAL  PHYSIOLOGY. 

now  treat  of  the  functions  of  a  portion  of  the  ear,  according  to 
onr  present  classification. 

Have  the  Semicircular  Canals  a  Co-ordinating 
Function  ? 

Physiologists  have  as  yet  been  unable  to  assign  to  the  semi- 
circular canals  a  function  in  hearing,  and  upon  certain  results, 
partly  of  disease  but  chiefly  of  experiment,  it  has  been  con- 
cluded, though  somewhat  dubiously,  that  they  are  concerned 
with  those  sensations  that  conduce  to  or  are  essential  to  main- 
tenance of  the  sense  of  equilibrium  ;  in  a  word,  that  they  are 
the  organs  of  that  sense  in  the  same  way  that  the  eye  is  the 
organ  of  vision. 

Experimental. — "When  in  a  bird,  as  a  pigeon,  one  of  the  mem- 
branous semicircular  canals  on  one  side  is  cut  through,  move- 
ments of  the  head,  varying  with  the  canal  cut,  result ;  though 
these  are  not  permanent,  when  the  operation  is  unilateral. 
After  the  bilateral  operation  a  bird  flies  with  difficulty,  eats  and 
drinks,  but  not  as  usual,  and  behaves  generally  in  a  way  to  in- 
dicate loss  of  co-ordination.  It  appears  to  be  dizzy.  It  can  hear 
well,  and  is  not  paralyzed,  nor  is  there  even  weakness  of  the 
muscles.  The  phenomena  in  other  animals,  while  not  quite  the 
same,  indicate  that  the  essential  failure  is  in  co-ordinatioii  of 
muscular  movements.  When  the  peculiar  movements  of  the 
head  or  eyes,  at  first  ensuing  on  operation,  are  permanent,  it  is 
possible  that  there  may  have  been  injury,  either  primary  or 
secondary,  to  the  cerebellum  or  other  parts  of  the  brain.  There 
are  very  many  ways  in  which  giddiness  and  consequent  inco- 
ordination may  be  induced  in  man  and  the  lower  animals. 
When  this  is  brought  about  by  rapid  rotation,  both  the  disturb- 
ance in  the  distribution  of  the  blood  within  the  cranium  and 
actual  displacement  of  brain-substance,  or  at  least  molecular 
disorder,  must  be  at  the  bottom  of  the  matter. 

In  Meniere's  disease,  vertigo  is  a  prominent  symptom  in 
certain  cases,  but  absent  in  others.  Again,  it  is  asserted  that 
vertigo  may  be  induced  in  animals  in  which  both  auditory 
nerves  are  divided.  For  our  own  part,  we  believe  an  undue  im- 
portance has  been  attached  to  the  semicircular  canals  in  the 
present  connection.  Experiments  on  animals  can  not  alone 
solve  such  problems  as  this,  for  the  reason  that  we  can  never 
know,  except  in  the  vaguest  way,  their  states  of  consciousness. 
Indeed,  the  latter  must  always  be  interpreted  by  our  own,  or 


THE   BRAIN.  503 

remain  inscrutable ;  so  that  it  follows  that  human  conscious- 
ness must  ])e  the  final  court  of  appeal ;  and  that  we  must  de- 
pend more  upon  clinical  and  pathological  investigation  than 
upon  experiment ;  but  even  this  is  not  final,  and  in  the  end  our 
own  conscious  experience  will  alone  enable  us  to  interpret  facts 
of  the  character  now  discussed.  Assume  that  a  human  subject 
has  been  operated  upon  as  above  indicated,  and  feels  so  dizzy 
that  he  is  unable  to  walk  steadily,  and  possibly  unable  to  re- 
main standing.  If  interrogated,  what  would  be  the  answers 
given  by  an  accurate  reporter,  with  no  bias  from  any  theory 
whatever  bearing  on  the  subject  ?  As  we  conceive,  somewhat 
as  follows  :  "  How  do  you  feel  ?  Why  can  you  not  rise  and 
remain  standing,  or  walk  ?  "  "  I  feel  all  confused.  I  can  not 
stand  or  walk  because  I  do  not  seem  to  be  able  to  make  out 
what  I  should  do.  I  have  no  clear  ideas  of  things  about  me, 
and  so  do  not  know  how  to  proceed."  Put  in  more  abstract  or 
generalized  form,  this  amounts  to  saying :  "  I  am  so  confused 
by  conflicting  sensations  that  all  my  old  judgments  about  the 
world  are  upset,  yet  memory  and  reason,  in  so  far  as  I  can  exer- 
cise them,  tell  me  that  they  are  wrong,  and  I  fear  to  act,  and  so 
remain  still ;  or,  when  I  do  try  to  stand  or  walk,  my  confusion 
leads  to  a  sort  of  loss  of  control  over  my  thoughts  and  feelings, 
and  therefore  my  will-power,  so  that  any  effort  to  walk  is  fee- 
bly directed  by  will,  and  little  regulated  by  my  usual  feelings ; 
hence  I  accomplish  little,  and  lose  confidence  in  myself/'  Such 
may  be  considered  an  attempt,  and  only  fairly  successful,  no 
doubt,  so  great  is  the  complexity  of  the  state  of  consciousness 
resulting,  to  describe  the  condition  of  a  human  being  under 
such  circumstances,  as  derived  from  a  consultation  with  our 
experiences  under  peculiar  conditions,  as  the  various  forms  of 
giddiness,  intense  and  sudden  surprise,  and  a  host  of  others  not 
readily  named  but  still  real.  With  a  bird  or  qiiadruped  the 
case  must  be  somewhat  similar. 

It  has  been  suggested  that  there  is  experimental  evidence  to 
show  a  power  of  estimation  of  the  distance  and  direction  through 
which  a  human  subject  is  moved,  independent  of  the  data  fur- 
nished by  other  senses,  as  sight,  tactile,  and  muscular  sensation, 
etc.  When  an  individual,  blindfolded,  lies  upon  a  flat  surface 
and  is  gently  rotated  through  a  certain  angle,  it  is  said  that  the 
subject  of  the  experiment  chti  make  a  fair  estimate  both  of  the 
direction  and  distance  through  which  he  is  moved,  from  which 
it  is  argued  that  there  is  a  sense  answering  to  this  result,  and 
locatf'd.  presuinably,  in  the  semicircular  canals.     But,  in  the 


504  ANIMAL  PHYSIOLOGY. 

first  place,  we  very  mucli  doubt  whether,  in  such  an  experi- 
ment, tactile  and  muscular  sensation  is  in  abeyance,  and,  in 
the  second  place,  if  it  were,  there  are  associated  sensations,  pos- 
sibly from  the  vascular  and  lymphatic  systems,  and  many 
other  sources  within,  which  can  not  be  ignored.  We  do  not 
even  yet  seem  to  be  sufficiently  alive  to  the  delicacy  and  the 
immense  variety  of  our  sensations,  some  of  which  are  abso- 
lutely indefinable ;  otherwise  we  do  not  think  such  experiments 
as  that  above  cited  would  be  adduced  in  proof  of  a  special 
sense  of  equilibrium. 

Until  further  evidence  is  forthcoming,  then,  we  are  not  in- 
clined to  give  assent  to  the  existence  of  any  mechanism  in  the 
semicircular  canals,  affording  sensory  data  so  entirely  different 
from  those  furnished  by  other  recognized  (and  unrecognized) 
sense-organs,  that  upon  them  alone,  or  in  a  manner  entirely 
their  own,  arises  a  consciousness  of  equilibrium.  We  are  in- 
clined to  regard  the  latter  as  depending  upon  the  fusion  in  con- 
sciousness of  a  vast  complex  of  sensations ;  and  that  upon  the 
whole  being  there  represented,  or  a  portion  wanting,  depends 
either  the  preservation  of  equilibrium,  or  a  partial  or  entire  loss 
of  the  same.  Nevertheless,  it  is  highly  probable  that  sensory 
impulses  of  a  very  important  character,  in  addition  to  such  as 
are  essential  for  hearing,  may  proceed  from  the  semicircular 
canals,  and  indeed  other  parts  of  the  labyrinth  of  the  ear. 

Forced  Movements. 

When  certain  portions  of  the  brain  of  the  mammal  have 
been  injured,  movements  of  a  special  character  result,  and, 
inasmuch  as  they  are  not  voluntary,  in  the  ordinary  sense  at 
least,  have  been  spoken  of  as  forced  or  compulsory.  The  move- 
ments may  be  classified  according  as  they  are  around  the  long 
vertical  or  the  transverse  axis  of  the  body  of  the  animal.  Hence 
there  are  "  circus  "  movements,  when  the  creature  simply  turns 
about  in  a  circle,  "  rolling  "  movements,  etc.  These  and  others 
may  be  toward  or  from  the  side  of  injury.  While  in  some 
cases  there  may  be  a  certain  amount  of  muscular  weakness  in 
consequence  of  the  injury,  which  may,  in  part,  account  for  the 
direction  of  the  movements,  this  is  not  so  in  all  cases ;  nor  does 
it,  in  itself,  explain  the  fact  of  their  being  plainly  not  volun- 
tary in  the  usual  sense. 

The  parts  of  the  brain,  which,  when  injured,  are  most  liable 
to  be  followed  by  forced  movements  are  the  basal  ganglia  (cor- 


THE  BRAIN.  505 

pora  striata  and  optic  thalami),  the  crura  cerebri,  corpora  qiiad- 
rigemina,  pons  Varolii,  and  medulla  oblongata,  and  especially 
if  the  section  be  unilateral.  We  have  already  seen  that  several 
of  these  parts  are  concerned  in  muscular  co-ordination ;  hence 
the  disorderly  character  of  any  movements  that  might  now  re- 
sult when  any  part  of  this  related  mechanism  is  thrown  out  of 
gear,  so  to  speak ;  but,  apart  from  that,  we  think  that  the  view 
presented  in  the  previous  sections  is  applicable  in  this  case 
also,  while  the  forced  movements  themselves  throw  light  upon 
the  symptoms  following  injury  to  the  semicircular  canals. 
When  that  constant  afflux  of  sensory  impulses  toward  the 
nervous  centers  is  interfered  with,  as  must  be  the  case  in  such 
sections  as  are  now  referred  to,  it  is  plain  that  the  balance  in 
consciousness  must  be  disturbed ;  confusion  results,  and  it  is 
not  surprising  that,  instead  of  a  passive  condition,  one  marked 
by  disorderly  movements  should  result  in  an  animal,  since 
movement  so  largely  enters  into  its  life-habits.  It  is  important 
to  remember,  in  this  connection,  that  the  great  highway  of  im- 
pulses between  the  cerebral  cortex  and  other  parts  of  the  brain 
and  the  spinal  cord  lies  in  the  very  parts  of  the  encephalon  we 
are  now  considering. 

Functions  of  the  Cerebral  Conyolutions. 

Comparative. — It  will  conduce  to  the  comprehension  of  this 
subject  if  some  reference  be  now  made  to  the  development  of 
the  brain  in  the  different  groups  of  the  animal  kingdom. 

Invertebrates  not  only  have  no  cerebrum,  but  no  brain  in 
the  strict  sense  of  the  term  as  applied  to  the  higher  mammals. 
In  most  forms  of  this  great  subdivision  of  the  animal  kingdom, 
the  first  or  head  segment  is  provided  with  ganglia  arranged  in 
the  form  of  a  collar  around  the  oesophagus,  by  means  of  com- 
missural nerve  connections;  so  that  the  nervous  supply  of  the 
head  is  not  widely  different  from  that  of  the  other  segments 
of  the  body.  But  as  we  ascend  in  the  scale  among  the  in- 
vertebrates these  ganglia  become  more  crowded  together,  and 
so  resemble  the  vertebrate  brain  with  its  massed  ganglia  and 
numerous  connections  through  nerve-fibers,  etc.  But  in  this 
respect  we  find  great  difference  among  vertebrates.  We  can 
recognize,  on  j^assing  upward  from  the  Amphioxus,  destitute 
of  a  brain  proper,  to  man,  all  gradations  in  the  form,  relative 
size,  multiplicity  of  connecting  ties,  etc. 

Speaking  generally,  tliere  is  great  difference  in  the  weiglit 


506 


ANIMAL  PHYSIOLOGY. 


iL^ 


i^WW^ 


\-^^-\-'\-lJ^^i 


Fig.  351. 


Fig.  350. 

Fig.  350.— Nervous  system  of  medicinal  leech  (after  Owen),  n,  double  supra-oesophageal 
ganglion  connected  with  rudimentary  ocelli  (6.  b)  by  nerves  ;  c,  double  infra-oesophageal 
ganglionic  mass,  which  is  continuous  with  double  ventral  cord,  having  compound  ganglia 
at  regular  intervals. 

Fig.  351.— Nervous  system  of  the  common  mussel  (after  Owen).  I,  labial  ganglia  connected 
by  a  short  commissure  above  and  in  front  of  mouth  ;  6,  6,  branchial  ganglia,  connected 
in  like  manner,  and  united  by  long  nervous  cords  (d,  d)  with  labial  ganglia  :  p,  bilobed 
"  pedal  ganglion  sending  branches  to  the  muscular  foot  (r),  and  closely  united  with  the 
"auditory  saccules"  (s)  ;  h,h\  circum-paUial  plexus;  y,  byssus,  by  which  the  animal 
can  attach  itself  to  foreign  bodies  (anchor) 


of  the  cerebrum,  both  relative  and  absolute.  In  all  animals  be- 
low the  primates  (man  and  the  apes)  the  cerebellum  is  either 
not  at  all  or  but  imperfectly  covered  by  the  cerebrum ;  while 
in  man,  so  great  is  the  relative  size  of  the  latter,  that  the 
cerebellum  is  scarcely  visible  from  above.  If  we  except  the 
elephant,  in  which  the  brain  may  reach  the  weight  of  ten 
pounds,  and  the  whale  with  its  brain  of  more  than  five  pounds 
in  the  largest  specimens,  the  brain  of  man  is  even  absolutely 
heavier  than  that  of  any  other  animal,  which  is  in  great  part, 
due  to  the  preponderating  development  of  the  cerebrum. 

While  the  cerebral  surface  is  smooth  in  all  the  lower  verte- 
brates, and  but  little  convoluted  until  the  higher  mammals  are 


THE  BRAIN. 


507 


Fio.  355. 

Fio.  a'ic. 

Fio.  35a.— Nervous  svmUtti  of  a  white  ant,  TemiPft  after  Oepenlmiir  anrl  LespSs). 

Fio.  353.— Nervou.s  Kyst<'iri  of  a  water  beetle,  f)i/ti.HruH  (after  fie«eiil>aur). 

Fio.  3.54.  -  NervoiiH  system  of  a  fly,  Mimra  (after  (iepenbaur  and  Hlanchard).    o.  eyes;  (/s, 

Kupra-(*;K<-)phai.'eal  Kan^lia  or  brain  ;  yi,  8ul)-(jeHophaj?eal  ganglion  ;  j/r,  grr",  gr^,  fused 

thora<;i(;  Kanfflia. 
Fio.  355. --Nervous  system  of  a  crab,  Pnlinuruji  i^iilr/nris,  showing  considerable  fusion  of 

ganglia  (after  .Milne-K/lwards).    «,  fused  (;erebral  ganglia;  />,/>,  long  oesophageal  cords; 

r.  r.  great  ventral  (.'anglionic  mass. 
lia.VA      Nervous  system  of  a  large  scorpion  like  spider,  Tlii'li/iihonus  rnudntus (after  Oegen 

baiir  and  lilanchard).    »,  cerebral  ganglia  ;  /,  great  ventral  ganglion  ;  o,  eyes  ;  ;>,  palpi; 

J'  -p",  feet. 


508 


ANIMAL  PHYSIOLOGY. 


Fig.  357.— Nervous  system  of  common  cuttle-fish,  Sepia  officinalis  (after  Owen).  1,  double 
supra-oesophageal  g;anglion  ;  p,  p,  cut  surfaces  of  the  cartilaginous  cranium  ;  2.  2,  optic 
ganglia  ;  4,  4,  posterior  sub-oesophageal  ganglia  ;  7,  8,  ganglia  in  connection  with  pharynx 
and  mouth  ;  13, 13,  great  motor  nerves  of  mantle,  etc.,  with  other  ganglia  ;  14,  c,  c,  respira- 
tory nerves.  The  intelligence  of  this  animal  is  in  proportion  to  the  size  and  concentration^ 
of  its  ganglia. 


Fig.  358.— Brain  and  cranial  nerves  of  perch,  seen  from  the  side  (after  Gegenhaur  and  Cuvier). 
A,  cerebral  lobe  with  olfactory  ganglion  in  front ;  B,  optic  lobe  :  C,  cerebellum  ;  D,  me- 
dulla oblongata ;  I—VIII,  nerves  in  usual  order  ;  X",  lateral  branch  of  vagus  ;  I,  upper 
twig  of  same ;  m,  dorsal  branch  of  trigeminus,  joined  by  n,  dorsal  branch  of  vagus ; 
a,  /3,  y,  three  branches  of  trigeminus  ;  Se,  facial  nerve  ;  A,  branchial  branches  of  vagus. 


THE   BRAIN. 


509 


reached,  the  brain  of  the  primates,  and  especially  of  man,  has 
its  surface  enormously  increased,  owing  to  its  numerous  fis- 
sures and  convolutions,  which,  in  fact,  arise  from  the  growth 
of  the  organ  being  out  of  proportion  to  that  of  the  bony  case 
in  which  it  is  contained ;  and  since  those  cells  which  go  to 


B,  cerebral  lobes  ; 
The  cerebellum  is 


Fig  :i59.— Brain  and  spinal  cord  of  frog  (Bastian).  A.  olfactdry  lobes  ; 
R.  pineal  bodj" ;  C,  D,  optic  lobes  ;  E,  cerebellum  ;  //,  spinal  cord, 
notably  small 


make  up  the  gray  matter  and  are  devoted  to  the  highest  func- 
tions, are  disposed  over  the  surface,  the  importance  of  the  fact 
in  accounting  for  the  superior  intelligence  of  the  primates, 
and  especially  of  man,  becomes  apparent.  Depth  of  fissuring 
is,  however,  of  more  importance  than  multiplicity  of  furrows  ; 
and  it  may  be  observed  that  intelligence  is  not  always  in  pro- 
portion to  the  extent  to  which  the  cerebral  surface  is  broken 


Fio.  361. 


Fio.  3fi0.— Brain  of  the  pike,  viewed  from  above  (Huxley).  A,  the  olfoctory  nerves  or  lobes, 
and  beneath  them  the  optic  nerves  ;  B,  the  cerebral  hemispheres  ;  C,  the  optic  lobes  ;  />, 
the  ceretielliirn. 

Fio.  3B1.— The  brain  of  edible  fro?  (Rava  psculenta).  1x4.  (After  Hti.vley.)  L.ol.  the 
rhinencephalon,  or  olfactory  lobes,  with  /.  the  olfactory  nerves  :  Hr.  the  cerebral  hemi- 
Kpheres  :  Fk.o,  the  thalamencei)halon  with  the  pineal  Kland.  Pn  :  L.op,  optic  lobes;  C, 
cerebellum  ;  .S'.  rh,  the  fourth  ventricle  :  Mo.  medulla  oblongata. 

up  into  fissures  and  convolutions.  The  depth  of  the  gray  mat- 
ter is  also  very  variable,  and  seems  to  bear  an  important  rela- 
tion to  psychic  development.  Man's  brain,  then,  is  character- 
ized by  its  great  size  and  complexity ;  while  those  parts  treated 


510 


ANIMAL  PHYSIOLOGY. 


Fy- 


Fig.  362.— a,  C,  the  brain  of  a  lizard  {Psammosaurus  Bengalensis),  and  B,  D,  of  a  bird  (Melea- 
gris  gallopavo,  the  turkey),  drawn  as  if  they  were  of  equal  lengths  (after  Huxley).  A,  B, 
viewed  from  above  ;  C,  D.  from  the  left  side.  Olf,  olfactory  lobes  ;  Pw,  pineal  gland  ; 
Hmp,  cerebral  hemispheres  ;  Mb,  optic  lobes  of  the  mid-brain  ;  C6,  cerebellum  ;  M,  O, 
medulla  oblongata;  ii,  iv,  vi,  second,  fourth,  and  sixth  pairs  of  cerebral  nerves ;  Py, 
pituitary  body. 


Fig.  363. — Brains  of  a  lizard  (Psanimosaurits  Bengalensis)  and  of  a  bird  (Meleagris  qallopava) 
in  longitudinal  and  vertical  section.  The  upper  figure  represents  the  lizard's  brain  ;  the 
lower,  that  of  the  bird  (after  Huxley  and  Carus).  Letters  as  in  the  preceding  figure, 
except  L.  t,  lamina  terminalis,  or  anterior  wall  of  the  third  ventricle  ;  /.  M,  foramen  of 
Munro  ;  a,  anterior  commissure  ;  Th.  E,  thalamencephalon  ;  .s,  soft  commissure  ;  p,  pos- 
terior commissure  ;  iv,  indicates  the  exact  point  of  exit  of  the  fourth  pair  from  that  part 
of  the  brain  which  answers  to  the  value  of  Vieussens. 


THE  BRAIN. 


511 


Fig.  364. 


Fig.  365. 


Fig.  366. 


Fig.  364.— Brain  of  pigeon  (after  Ferrier).  A,  cerebral  hemispheres  ;  B,  optic  lobe  ;  C,  cere- 
bellum, the  lateral  lobes  of  which  are  very  small. 

Fig.  365.— Brain  and  spinal  cord  of  chicle  at  sixteen  days  old  ;  optic  lobes,  b,  are  still  in  con- 
tact (after  Owen  and  Anderson*. 

Fig.  366.— Brain  and  part  of  spinal  cord  of  chick  twenty  days  old,  showing  optic  lobes  widely 
separated  and  cerebellum,  c,  largely  developed. 

elsewhere,  concerned  in  co-ordination,  vision,  etc.,  are  well 
developed,  tlie  cerebrum,  especially  its  lobes  as  distinguished 
from  its  basal  ganglia,  is,  out  of  all  proportion,  greater  than 
in  any  other  animal. 


Fifi    •■!'1K 


Fig.  367.— Outer  surface  of  brain  t<f  horw  Rafter  Solly  and  I.euref).  p,  olfactory  lobo  ;  h.  hip- 
pfwampal  lobe  (processus  pyriforrnis) ;  1.2.3,  lobes  of  <M'r('bellum  ;  o,  opti<!  nerve;  m, 
motfir  oi:u1i  :  //.  fourth  nerve  ;  /.  fifth  nerve  ;  u,  sixth  nerve  ;  /.  facial  :  /.  auditory  ;  g, 
(fl'«s/^>-pharvrigca1  :  v,  va^uH  :  x.  spinal  accessory  ;  n.  hypoglossal  :  X  pons  Varolii. 

Fig.  fji'iH.  I^iniritudiiial  sj-ctlrm  through  center  f)f  brain  of  horse,  presenting  view  of  internal 
Kiirface  <aft«T  Solly  and  I>'uret).  c.c,  cf)rpus  callosnin  :  ;».  tnalamuB  ;  ro,  middle  com- 
ml.HKure  :  /.  7.  corpora  ()ua<lrigemina,  in  front  of  which  Is  the  i)lneal  body.  The  cerebel- 
lum has  been  cut  through. 


512 


ANIMAL   PHYSIOLOGY. 


The  gray  matter  of  tlie  brains  of  the  higher  vertebrates  is 
distributed  as  masses  of  ganglionic  cells  internally,  and  as  a 
fairly  uniform  layer  over  its  surface.    The  cerebrum  of  man 


Fig.  369.— Lateral  views  of  the  brains  of  a  rabbit,  a  pig.  and  a  chimpanzee,  drawn  of  nearly 
the  same  absolute  size  (Huxley).  The  rabbit's  brain  is  at  the  top ;  the  pig's,  in  the  middle ; 
the  chimpanzee's,  lowest.  01,  olfactory  lobe  ;  A.  frontal  lobe  ;  5,  occipital  lobe  ;  C,  tem- 
poral lobe  ;  Sy.  the  sylvian  iissure  ;  In,  the  insula  ;  8.  Or,  supra-orbital ;  S.  F,  M.  F,  I.  F, 
superior,  middle,  and  inferior  frontal  gjTi ;  A.P,  antero-parietal ;  P.  P,  postero-parietal 
gyri ;  R,  sulcus  of  Rolando  ;  P.  PI,  postero-parietal  lobule  ;  O.  P/,, external  perpendicular 
or  occipitotemporal  sulcus  :  An.  angular  gyrus  :  3,  3,  4,  annectent  gyri ;  A.  T,  M.  T,  P.  T, 
the  three  temporal,  and  8.  Oc,  M.  Oc'  I.  Oc,  the  three  occipital  gyri. 


weighs  about  three  pounds  on  the  average,  that  of  the  male 
being  a  few  ounces  (four  to  six)  heavier  than  that  of  the  female. 
The  individual  and  race  differences,  though  considerable,  are 


THE   BRAIN. 


513 


not  comparable  in  degree  to  those  that  distinguish  man  from 
even  the  highest  apes,  the  brain  of  the  latter  weighing  not 
more  than  about  one  third  as  much  as  that  of  the  human  sub- 
ject. While  it  has  been  shown  that  individual  men  and  women 
may  reach  even  distinction  in  the  intellectual  world,  having 


Fio.  370.— Inner  views  of  cerebral  licniisplieres  of  the  rabbit,  pig,  and  chimpanzee,  drawn  as 
before,  and  placed  in  the  same  ordi-r  (Huxley).  <)l,  olfactory  lobe ;  C.  r,  corpus  callosum  ; 
A.r.  anti'rior  commissure  :  //,  hippocampal  sulcus  ;  6'/t,  uncinate  ;  Af.  marginal ;  C,  cal- 
losal  gyri  ;  /.  P,  internal  i>eriK;ndicular  ;  Co,  calcarine  ;  Coll,  collat«'ral  sulci ;  /<',  fornix. 

brains  of  average  or  even  sub-medium  weight ;  and  while  idiots 
have  been  known  to  possess  brains  abnormally  heavy,  it  is 
nevertheless  trne  that  brain-weight  and  the  higher  powers  of 
man  bear  a  close  though  not  invariable  rcilationship.  The 
apparent  discrepancies  are  susceptible  of  explanation. 
88 


514: 


ANIMAL  PHYSIOLOGY. 


^^ 


CO' 


CS'. 


— n./7U 


Fig.  372. 


Fig   371  -Brain  of  chimpanzee,  part  of  right  hemisphere  being  cut  away  so  as  to  expose 

ma  or  fn  desSing  cornu  f  ;.m,  hippocampus  minor  m  posterior  cornu  ;  i-^?reat^o°g^; 
tudinal  Assure;  F,  frontal,  P,  parietal,  O,  occiPital  lobes  Bfesure  ot  gom^ao^j  ^^ 
external  perpendicular  fissure  ;  X,  operculum  \  A,  A,  ascending  frontal ,  B,  B.  ascenamg 
parietal  convolution. 


THE  BRAIN. 


515 


Fio.  S'.r,. 


Fifi.  373.- Hrain  of  orariK.  Mi'l**  vit-w  (aftt-r  Vn^t  and  Oratiolct). 

Fio.  374.     Brain  of  a  Mot tcritnt  woman. 

Fio.  37.')  Brain  of  fiaiiKs.  the  ct-lebraUMl  rnatlK-inatician  and  astronomer  fafter  Vo^t  and 
R.  Watfnni).  The  difTerence  lietween  this  last  brain  anil  the  two  floured  ahove  will  not 
fail  t/i  Htrike  any  oLwrver.  Tliew  flKiireH  are  intended  to  illuHtraU;  ra<liil  and  Indivi.lual 
difrerene«'H  on  the  one  hand,  and  the  ^reaU-r  rewri bianco  to  lower  fornm  of  the  brain  of 
the  more  de^^raded  races  of  mi-n. 


516 


ANIMAL  PHYSIOLOGY. 


mMm.i 


iiu 


Fig.  3,6.— Vertical  section  of  third  cerebral  convolution  in  man  (after  Meynert)  1  super- 
ficial cells  ;  2,  layer  of  small  pyramidal  cells  ;  3,  layer  of  large  pyramidal  cells  :  4,  Ifiver 
of  small  irregular  cells  ;  5,  layer  of  spindle-shaped  cells  ;  M,  white  substance. 


THE   BRAIN. 


517 


Besides  the  gray  matter,  with  its  cells  of  highest  functional 
value  from  the  standpoint  now  taken,  the  brain  consists,  and 
in  large  part,  of  neuroglia  and  nerve-fibers,  with  probably 


Fir. 


Fig  377  -Diaerammatic  horizontal  section  of  a  vertebrate  brain  (Huxley V  The  following 
letters  serfe  for  both  this  figure  and  the  one  following.  Mb.  mid-brain  What  lies  in  front 
of  iw^  ^Uie  fore-brain,  and  what  hes  behind^  the  hind-brain.  L  t  the  lannna  termmahs  ; 
Olf  olfactory  lobes:  Hmp,  hemispheres;  Th.  E,  thalamencephalon  ;  Pri,  pineal  gland  . 
PV.'p  u1S?7body  ;  FM.  foramen  of  Munro  ;  CS,  corpus  striatum:  //,,  optic  tha  amus  ; 
CO  coroora  nuadrigemina  ;  CC,  crura  cerebri  ;  Cb.  cerebellum  :  Pl\  pons  Varolii  ,^0, 
medulla  oblongata  :  /,  olfactorii  ;  //,  optici ;  IIL  point  of  exit  from  brain  of  motores  oculo- 
Sirn  ;  /r  of  pathetic  ;  VI.  of  abducentes  ;  V-XII,  origins  of  the  other  cerebra  neryea^ 
^  olfkctory  ventricle  ;  2,  lateral  ventricle  ;  3,  third  ventricle  ;  4.  fourth  ventricle  ;  +,  tier 
a  tertio  ad  quurtum  ventriculum. 


v-:zir 


j!,r.    "*-«      i  if.ntHtiidinftl  and   vertical  section  of  a  vertebrate  brain  (Huxley).    Letters  M 
''■^  J?^« -^T!;:^Sr<erm!urx1);i«  re^esented  by  the  strong  blaclc  line  between  FM  and  3. 


above. 


chiefly,  and  in  the  case  of  the  fibers  solely,  a  conducting  func- 
tion. It  will  app(;ar  that  body-weight  must  be  taken  mto 
account  in  comparing  the  brains  of  the  sexes  and  of  indi- 
viduals.    Again,  tlie  quality  or  functional  capacity  of  the  indi- 


518  ANIMAL  PHYSIOLOGY. 

vidual  elements,  especially  of  the  cortical  cells,  both  as  the  re- 
sult of  innate,  inherited  powers,  and  as  altered  by.  education, 
is,  of  course,  a  matter  of  great  importance.  By  education  we 
mean  all  those  influences  that  have  been  brought  to  bear  upon 
these  cells  from  without,  of  whatever  kind.  Apart,  too,  from 
all  these  considerations,  it  must  be  clear  that  what  any  set  of 
cells  can  accomplish,  be  they  brain-cells  or  other,  must  depend 
largely  upon  their  capacity  to  appropriate  nourishment,  which 
will  in  turn  be  modified  by  blood-supply,  the  behavior  of  ex- 
creting organs,  etc.  In  a  word,  the  intellectual  achievements 
are  dependent  on  a  great  variety  of  factors.  The  brain  and 
other  parts  are  so  mutually  dependent  that  they  can  not  be  un- 
derstood by  any  isolated  consideration  of  the  one  or  the  other. 
It  is  not  to  be  supposed  that  an  individual  with  a  poor  respir- 
atory, circulatory,  and  digestive  system,  no  matter  what  the 
possibilities  of  his  cerebrum,  can  ever  rank  with  an  organism 
admirably  balanced  in  these  respects. 

The  Connection  of  one  Part  of  the  Brain  with  another. — Though 
it  has  long  been  known  that  the  different  parts  of  the  brain 
were  connected  by  bridges  of  fibers  {commissures,  etc.),  the 
physiological  significance  of  the  fact  seems  to  have  been  largely 
ignored,  and  even  at  the  present  day  is  too  little  considered. 
1.  Cerehral  fibers  pass  between  the  convolutions  of  this  part  of 
the  brain  and  the  cerebellum ;  between  the  former  and  the  main 
basal  ganglia ;  between  the  gray  matter  of  the  convolutions  on 
the  same  side,  and  between  the  latter  and  those  on  the  opposite 
halves ;  between  the  gray  matter  of  the  cortex  and  the  internal 
capsule,  the  corpora  striata,  optic  thalami,  pons  Varolii,  the 
medulla  oblongata,  and  so  to  the  spinal  cord.  The  course  of 
the  latter  tracts  of  fibers  have  been,  especially  by  the  help  of 
pathology,  definitely  followed.  Some  of  these  connections  are 
given  in  more  detail  below  : 

1.  Cerehro-cerebellar  fibers,  (a.)  From  the  cortical  cells  of 
the  anterior  cerebral  lobe  to  the  pons  Varolii,  passing  through 
the  internal  capsule  and  thence  through  the  lower  and  outer 
part  of  the  crus  cerebri  (crusta).  (b.)  Fibers  from  the  occipital 
and  temporo-sphenoidal  lobes,  passing  by  the  crusta,  reach  the 
upper  surface  of  the  cerebellum. 

2.  Fibers  bridging  the  two  sides  of  the  cerebrum,  (a.)  By 
means  of  the  corpus  callosum  chiefly,  passing  from  the  gray 
matter  in  the  first  instance,  (b.)  From  the  temporo-sphenoidal 
lobe  on  each  side  through  the  corpora  striata  and  anterior  com- 
missure,    (c.)  Fibers  from  the  upper  part  of  the  crus  cerebri 


THE   BRAIN, 


519 


[tegmentum)  to  the  optic  thalamus  of  each  side  and  onward 
to  the  temporo-sphenoidal  lobes,  forming  the  posterior  commis- 
sure. 

3.  Fibers  connecting  different  parts  of  the  cerebral  convolu- 
tions on  the  same  side.  These  are  exceedingly  numerous  and 
are  effected  by  such  tracts  as  the  "  arcuate  fibers/'  passing  from 
one  gyrus  to  another ;  "  collateral  fibers,"  forming  distant  convo- 
lutions ;  fibers  of  the  fornix  between  the  uncinate  gyrus,  hip- 
pocampus major,  and  optic  thalamus ;  longitudinal  fibers  of  the 
corpus  callosum ;  fibers  of  the  tsenia  semicircularis,  uncinate 
fasciculus,  etc. 

4.  Fibers  forming  the  cerebrum  and  the  spinal  cord.  Ac- 
cording as  they  pass  downward  or  upward  do  they  converge  or 
diverge,  and  the  most  important  seem  to  pass  through  the  in- 
ternal capsule ;  and  while  the  majority  do  perhaps  form  some 
connection,  either  with  the  corpora  striata  and  optic  thalami. 


Fio.  37''J.— Diajframrnalic  repreBenlation  of  the  coiir«e  of  some  of  thr-  f[hcrn  in  the  ccrHbriini 

(afUr  Le  Bou). 


520 


ANIMAL   PHYSIOLOGY. 


some  seem  to  pass  directly  downward  through  the  internal  cap- 
sule. It  is  held  by  many  that  the  fibers  passing  through  the 
posterior  portion  of  the  internal  capsule  are  derived  from  the 
posterior  lobe  of  the  cerebrum,  and  are  the  paths  of  sensory  im- 
pulses upward ;  while  the  rest  of  the  internal  capsule  is  made 
up  of  fibers  from  the  anterior,  and  especially  the  middle  portion 
of  the  cerebral  cortex  (motor  area),  and  these  fibers  are  the 
paths  of  motor  (efferent)  impulses. 

It  now  becomes  clearer  that  the  brain  is  constituted  a  whole 
by  such  connections ;  and  that,  apart  from  the  multiplicity  of 
cells  with  different  functions  to  perform,  situated  in  different 
areas,  the  complexity  and  at  the  same  time  the  unity  of  the 
encephalon  becomes  increasingly  evident,  merely  upon  anatomi- 
cal grounds ;  but  we  shall  find  such  a  view  still  further  strength- 
ened by  study  of  the  functions  of  the  various  parts.  While  the 
tracts  enumerated  are  anatomical  and  have  been  clearly  traced, 
there  can  be  little  doubt  that  many  others  yet  remain  to  be 


CALLOSO-MARGINAL  SULCUS 


""''f^P"^*^ 


^FISSURE  OFROLANDU 


ANTERIOR  CRUS 
OF  FORNI 


PARIETO- 
OCCIPITAL 
SSURC 


4'"  VENTRICLE 


PINEAL  GLAND. 
CORPORA  OUADRISEMINA' 
Fig.  380.— Median  longitudinal  section  of  human  brain,  semi-diagrammatic  (after  Flint). 


marked  out ;  and  that,  apart  from  such  collections  of  fibers,  we 
must  recognize  functional  paths  by  the  neuroglia,  and  possibly 


THE  BRAIN. 


521 


others  still.  It  is  not  to  be  forgotten  that  in  the  brain,  as  in  the 
spina]  cord,  nerve-cells  are  themselves  conductors,  and  while 
there  may  be  certain  areas  within  which  the  resistance  is  such 
that  impulses  are  usually  confined  to  them,  it  is  also  true  that, 
as  in  the  cord,  there  may  be  a  kind  of  overflow.  Adjacent  cells, 
possibly  widely  separated  cells,  may  become  involved.  We  shall 
return  to  this  important  subject  again,  however,  as,  without 
recognizing  such  relationships,  it  seems  to  us  quite  impossible 
to  understand  the  facts  as  we  find  them  in  the  working  of  the 
body  and  the  mind. 

The  Cerebral  Cortex. — We  may  now  proceed  to  inquire  what 
are  the  functions  of  the  cells  of  the  gray  matter  covering  the 
surface  of  the  cerebrum.  Before  the  birth  of  physiology  as  a 
science,  Gall  recognized  and  taught  that  the  encephalon  is  a  col- 


Fio.  .381.— Diafn'animatic  rppresentation  of  external  surface  of  left  cerebral  hemisphere  of 
man  'after  Flint  and  Ecker). 

lection  of  organs ;  that  these  have  separate  functions ;  that  the 
relative  size  of  each  determines  the  degree  of  its  functional  ac- 
tivity, and  that  the  cranium  developing  in  proportion  to  the 
growth  of  the  brain,  the  former  might  give  information  as  to 
the  probable  size  of  what  lay  beneath  it  in  different  regions. 


522 


ANIMAL   PHYSIOLOGY. 


It  will  be  seen  that,  as  thus  interpreted,  phrenology  is  a  very 
different  thing  from  what  usually  passes  under  that  name,  and 
is  paraded  before  wondering  audiences  by  ignorant  charlatans. 
In  the  main  the  doctrines  of  Gall  are  not  without  a  certain 
foundation  in  facts ;  and  the  modern  theory  of  localization  of 
function  bears  a  strong  resemblance  to  what  Gall  taught, 
though  with  greater  limitations. 


Temvof" 


Fig.  382.— Diagrammatic  representation  of  internal  surface  of  right  cerebral  liemispliere,  as 
seen  in  vertical  longitudinal  median  section  (after  Flint  and  Ecker). 

Among  the  more  modern  observers,  Flourens  held  that  re- 
moval of  small  portions  of  the  cerebral  cortex  produced  no 
effect  on  either  will-power  or  intelligence,  but  that  if  carried 
far  enough  both  volition  and  intelligence  were  completely  de- 
stroyed. Later  observers,  say,  of  ten  years  ago,  maintained 
that  the  whole  or  the  grea^ter  part  of  the  cerebral  cortex  might 
be  mapped  out  into  areas  with  a  definite  function.  The  meth- 
ods of  investigation  have  been  clinico-pathological  and  physio- 
logical. 

It  was  found  that,  on  stimulating  certain  areas  of  the  cortex' 
(e.  g.,  the  so-called  motor  area),  certain  movements  followed, 
but  that  similar  results  were^obtained  when  the  electrodes  were 
applied  directly  to  the  white  matter  underlying  the  cortex ; 
hence  the  results  of  such  experiments  were  not  conclusive.  It 
was  held  that,  if  certain  regions  thus  respondent  to  a  stimulus 
were  removed,  the  movements  of  corresponding  muscles  should 
be  abolished ;  in  other  words,  there  should  be  localized  paraly- 


THE   BRAIN.  523 

sis.     It  was  then  asserted  by  certain  experimenters  tliat  such 
was  the  case,  while  others  strenuously  denied  this.     By  com- 


FiG.  383.— Outer  surface  of  cerebrum  (after  Exner).  The  shaded  portion  represents  the  motor 
in  man  and  the  monkey — i.  e.,  the  area  which  most  observers  believe  to  be  associated  with 
certain  voluntary  movements  of  the  limbs,  etc. 

bining  the  method  of  stimulation  with  that  of  ablation  (or  the 
removal  of  definite  portions  of  the  cortex),  a  very  extensive 
localization  was  established  by  certain  observers  (Hitzig,  Fer- 
rier,  etc.).  This  was  not  confined  to  motor  functions,  but  in- 
volved sensory  ones. 

On  the  other  hand,  one  physiologist  (Goltz)  has  from  the 
fir.st  maintained,  as  the  result  of  experiments  on  the  dog,  that 
localization  of  the  character  described  by  the  above-mentioned 
observers  does  not  exist.  He  finds  that  no  amount  of  ablation 
of  the  cerebrum  will  lead  to  paralysis,  and  that,  if  lesions  in 
any  part  be  but  extensive  enough,  the  sensory  perceptions  and 
the  intelligence  of  the  animal  are  impaired.  It  is  found  that 
the  movements  of  dogs,  after  tlie  removal  of  a  considerable  por- 
tion of  the  cerebral  cortex  are  awkward  ;  that  one  or  all  of  the 
animal'.s  sensory  perceptions  may  be  impaired  ;  that,  in  fact, 
the  creature  may  be  reduced  to  a  mere  eating  and  drinking 
machine,  as  it  were ;  but  that  paralysis  proper  does  not  exist. 


524  ANIMAL   PHYSIOLOGY. 

About  the  same  time  another  experimenter  (Munk)  had 
been  attempting  to  map  out  the  region  of  the  cortex  concerned 
in  vision.  As  a  result  of  removal  of  different  portions  of  the 
occipital  lobe  in  dogs,  he  had  concluded  that  a  portion  of  this 
lobe  constituted  the  cortical  visual  center,  and,  further,  that 
the  blindness  resulting  from  such  operations  as  are  now  under 
consideration  was  either  "  absolute  "  or  "  psychical " ;  by  which 
was  meant,  in  the  first  instance,  an  inability  to  bring  the  images 
of  the  retina  into  consciousness,  and,  in  the  second,  inability  to 
interpret  visual  sensations  intelligently,  the  one  or  the  other 
result  being  dependent  on  the  part  of  the  limited  visual  center 
that  was  removed.  This  may  be  regarded  as  perhaps  the  most 
extreme  form  of  sensory  localization  yet  taught. 

Goltz,  as  a  result  of  his  latest  experiments,  not  only  denies 
that  operations  on  the  occipital  lobe  are  peculiar  in  producing 
visual  disturbances,  but  points  out  that  these  lead  to  sensory 
defects  overlooked  by  Munk.  This  observer  (Goltz),  as  a  result 
of  comparing  a  dog,  with  both  anterior  cerebral  lobes  removed, 
with  others  from  which  were  removed,  in  the  one  case,  the 
right,  and  in  the  other  the  left  corresponding  parts  (anterior 
cerebral  lobes),  since  he  finds  the  dog  with  both  removed  in  a 
worse  condition  than  would  be  represented  by  the  joint  result 
of  the  addition  of  the  imperfections  of  the  other  two,  concludes 
that  one  cerebral  lobe  may,  to  a  certain  extent,  take  up  the 
functions  of  another.  In  other  words,  he  admits  localization 
but  only  of  the  roughest  kind. 

A  view  advanced  by  Schiif  deserves  probably  more  consid- 
eration than  it  has  received,  viz.,  that  motor  areas  are  so  related 
to  tactile  sensations  arising  in  different  parts  of  the  body  that 
when  the  former  are  stimulated  the  resulting  movements  are 
really  reflex — i.  e.,  the  stim.ulation  of  the  cortex  replaces  the 
afferent  sensory  impulses,  which  usually  are  associated  with 
the  movements  in  question. 

In  the  mean  time  it  has  been  found  that  in  many  cases  it 
was  possible  to  locate  the  site  of  a  brain-lesion  (tumor,  etc.)  by 
the  symptoms,  chiefly  motor,  of  the  patient ;  and  brain-surgery 
has  in  consequence  entered  upon  a  new  era  of  development. 
Tumors  thus  localized  have  been  removed  successfully,  and  the 
patients  restored  to  health.  As  a  result  of  the  various  kinds  of 
observations  and  discussions  on  this  subject  of  late  years,  the 
localizationists  are  willing  to  admit  that  the  areas  of  the  cortex 
can  not  be  marked  off  mathematically — that,  in  fact,  they 
"  overlap."    This  is  in  itself  an  important  concession.    Again, 


THE  BRAIN.  525 

there  is  less  confidence  in  the  location  of  the  various  sensory 
centers  than  of  the  motor  centers.  Most  investigators  are  be- 
lievers in  a  "  motor  area  "  par  excellence  (for  the  arm,  leg,  etc.) 
around  the  fissure  of  Rolando.  This  view  is  now,  so  far  as 
man  is  concerned,  widely  accepted. 

There  is  agreement  in  placing  the  sensory  centers  behind 
the  above-mentioned  motor  area,  and  especially  in  the  occipital 
lobes.  The  tendency  to  locate  a  visual  center  in  this  region  is 
growing  stronger.  There  is  much  disagreement  as  to  the  other 
sensory  centers  formerly  placed  in  the  angular  gyrus  and  tem- 
poro-sphenoidal  lobes.  The  intellectual  faculties  have  not  been 
located  in  any  such  sense  as  Gall  and  his  followers  attempted 
to  establish.  The  first  two  frontal  convolutions  are  those  jjer- 
haps  to  which  localization  has  as  yet  been  least  applied.  Chiefly 
on  clinical  and  pathological  grounds  a  center  for  speech  has  long 
been  located  in  the  third  (left)  frontal  convolution  (Broca's)  and 
parts  immediately  behind  it.  It  has  been  observed  that,  when 
disease  attacks  this  area,'speech  is  interfered  with  in  some  way. 

We  may  say  then,  generally,  that  the  tendency  at  the  present 
time,  both  on  the  part  of  physiologists  and  clinical  observers,  is 
to  admit  localization  to  some  degree  and  in  some  sense.  This 
has  been  the  result  in  part  of  experiments  on  the  dog  and  es- 
pecially on  the  monkey,  combined  with  the  discussion  of  clini- 
cal cases  which  resulted  in  death  (followed  by  an  autopsy),  or 
of  others  marked  by  a  successful  diagnosis  and  removal  of 
lesions  or  other  treatment.  In  other  words,  the  truth,  if  it  will 
be  reached  at  all,  must  be  reached  by  the  method  we  have  ad- 
vocated throughout  this  work — the  discussion  of  the  results  of 
as  many  different  methods  as  can  be  brought  to  Tjear  on  this  or 
any  other  subject.  Neither  the  experimental  nor  the  pathologi- 
cal method  can  settle  such  complex  questions,  as  we  shall  en- 
deavor to  sliow  wliOM  we  return  to  the  subject  later. 

The  Circulation  in  the  Brain. — The  brain,  being  inclosed  within 
an  air-tight  bony  case,  its  circulation  is  of  necessity  peculiar. 
Since  any  undue  compression  of  the  encephalon  may  lead  to 
even  a  fatal  stupor,  it  is  clear  that  there  must  exist  some  pro- 
vision to  permit  of  the  excess  of  arterial  blood  that  is  required 
for  unusual  activity  of  the  brain.  It  is  to  be  borne  in  mind 
that  the  fluid  within  the  ventricles  is  continuous,  through  the 
foramen  of  Majendie  in  the  roof  of  the  fourth  ventrichi,  with 
that  surrounding  the  spinal  cord  (spinal  cavity) ;  so  that  an 
increase  in  the  volume  of  the  encephalon  in  consequence  of  an 
afflux  of  blood   might  bo  in  .some  degree  c'nTipensated  by  an 


526  ANIMAL   PHYSIOLOGY. 

efflux  of  the  cerebro-spinal  fluid.  The  part  played  by  this  ar- 
rangement has,  however,  been  probably  overestimated.  But 
the  peculiar  venous  sinuses  do,  it  is  likely,  serve  to  regulate 
the  blood-supply ;  being  very  large,  they  may  answer  as  tem- 
porary overflow  receptacles.  An  inspection  of  the  fontanelles 
of  an  infant  reveals  a  beating  corresponding  with  the  pulse ; 
and,  when  a  large  part  of  the  cranium  is  removed  in  an  animal, 
a  plethysmograph  shows  a  rise  in  volume  corresponding  with 
the  pulse  and  the  respiratory  movements,  as  in  the  case  of  the 
fontanelles.  But,  besides  these,  periodic  waves  of  contraction 
are  now  known  to  pass  over  the  cerebral  arteries. 

"Whether  the  latter  is  part  of  a  general  wave  traversing  the 
whole  arterial  system  is  as  yet  uncertain.  Though  there  is 
considerable  anastomosis  of  vessels  in  the  encephalon,  it  is  not 
equal  to  what  takes  place  in  many  other  organs.  It  is  well 
known  that  a  clot  or  other  plug  within  a  cerebral  vessel  is 
more  serious  than  in  many  other  regions,  which  is  partly  to  be 
explained  by  the  lack  of  sufficient  anastomosis  for  the  vascular 
needs  of  the  jjarts.  It  is  also  well  known  that,  in  organs  which 
constitute  parts  of  a  related  series,  as  the  different  divisions  of 
the  alimentary  tract,  all  are  not  usually  at  the  same  time  vas- 
cular to  the  same  extent.  While  they  act  functionally  in  rela- 
tion to  each  other,  they  exemplify  also  a  certain  degree  of  inde- 
pendence. Such  a  condition  of  things  is  now  known  to  exist  in 
the  brain — i.  e.,  certain  areas  maybe  abundantly  supplied  with 
blood  as  compared  with  others ;  and  it  seems  highly  probable 
that  a  condition  of  equal  arterial  tension  throughout  is  scarcely 
a  normal  condition.  Though  the  quantity  of  blood  contained 
within  the  vessels  of  the  whole  brain  at  any  one  time  is  not  so 
large  as  in  some  other  organs  (glands),  yet  the  foregoing  facts 
and  the  rapidity  of  the  flow  must  be  taken  into  account.  The 
capillaries  are  very  close  and  abundant,  in  the  gray  matter  es- 
pecially ;  and  it  is  to  be  borne  in  mind  that  it  is  chiefly  these 
vessels  which  are  concerned  in  the  actual  metabolism  (nutri- 
tion) of  parts.  However,  the  chemical  changes  in  the  nervous 
system  being  feeble,  it  would  appear  probable  that  it  does  its 
work  with  less  consumption  of  pabulum  than  other  parts  of 
the  body.  We  wish  to  lay  stress  on  the  local  nature  of  vas- 
cular dilatation  in  the  brain  as,  it  greatly  assists  in  explaining 
certain  phenomena  about  to  be  considered. 

Sleep. — Observations  upon  animals  from  which  portions  of 
the  cranium  had  been  removed,  so  that  the  brain  was  visible, 
show  that  during  sleep  the  blood-vessels  are  much  less  promi- 


THE  BRAIN.  527 

nent  tlian  usual ;  and  it  is  well  known  that  means  calculated  to 
diminish  the  circulation  in  the  brain,  as  cold  and  pressure,  favor 
sleep.  It  is  also  well  established  by  general  experience  that 
withdrawal  of  the  usual  afferent  impulses  through  the  various 
senses  favors  sleep.  A  remarkable  case  is  on  record  of  a  youth 
whose  avenues  for  sensory  impressions  were  limited  to  one  eye 
and  a  single  ear,  and  who  could  be  sent  to  sleep  by  closing 
these  against  the  outer  world.  Yet  this  subject  after  a  long 
sleep  would  awake  of  his  own  accord,  showing  that,  while  affer- 
ent impulses  have  undoubtedly  much  to  do  with  maintaining 
the  activity  of  the  cerebral  centers,  yet  their  automaticity  (in- 
dependence) must  also  be  recognized. 

It  is  a  matter  of  common  experience  that  weariness,  or  the 
exhaustion  following  on  pain,  mental  anxiety,  etc.,  is  favor- 
able to  sleep. 

A  good  deal  of  light  is  thrown  on  this  subject  by  hiberna- 
tion, particularly  in  mammals. 

From  special  study  of  the  subject  we  have  ourselves  learned 
that,  however  temperature  and  certain  other  conditions  may 
influence  this  state,  it  will  appear  at  definite  periods  in  de- 
fiance, to  a  large  extent,  of  the  conditions  prevailing.  Hiber- 
nation, we  are  convinced,  is  marked  by  a  general  slowing  of  all 
of  the  vital  processes  in  which  the  nervous  system  takes  a 
prominent  part.  Sleep  and  hibernation  are  closely  related.  In 
both  there  is  a  diminution  of  the  rate  of  the  vital  processes,  as 
shown  by  the  income  and  output,  measured  by  chemical  stand- 
ards, with  of  course  oljvious  physical  signs,  as  slowed  respira- 
tion, circulation,  etc.  While  sleep,  then,  is  primarily  the  re- 
sult of  a  rhythmical  retardation  of  the  vital  processes,  especially 
within  the  nervous  system,  it  is  like  hibernation  in  some  de- 
gree (In  the  lowest  creatures,  without  a  nervous  system)  the 
outcome  of  that  rhythm  impressed  on  every  cell  of  the  organ- 
ism and  the  influence  of  which  is  felt  in  a  thousand  ways,  that 
no  doubt  we  are  quite  unable  to  recognize. 

Dreaming  is  a  partial  activity  of  the  mind,  corresponding 
doubtless  to  functional  wakefulness  or  relatively  increased  ac- 
tion of  som(!  limited  part  or  parts  of  the  brain.  It  is  now  all  but 
certain  that  tlieso  i)arts  are  more  vascular — i.  e.,  we  must  reckon 
with  a  localized  vascularity  and  functional  activity.  If  this  be 
recognized,  almost  all  the  peculiarities  of  the  dreaming  state 
may  be  understood.  Dreams  usually  lack  some  elements  that 
give  the  completeness  and  consistency  of  waking  thought — a 
matter  readily  understood,  as  well  as  the  unrest  of  a  dreamy 


528  ANIMAL  PHYSIOLOGY. 

night,  by  the  facts  above  considered.  It  is,  moreover,  highly 
probable  that  not  only  different  parts  of  the  brain  have  a  dif- 
ferent psychical  function,  but  also  that  in  any  one  chain  of 
thought  or  state  of  consciousness  only  a  certain  number  of  parts 
are  prominently  engaged ;  and  that  what  is  termed  confusion 
of  mind  is  probably  a  result  of  the  activity  of  certain  other 
centers  to  a  degree  unusual — i.  e.,  they  are  relatively  too  obtru- 
sive^ hence  that  balance  essential  to  all  normal  activity,  psy- 
chical and  other,  is  lost. 

Specialization,  physiological  division  of  labor,  holds  here  as 
elsewhere. 

Hypnotism. — By  the  help  of  the  above  principles  the  subject 
of  hypnotism,  now  of  absorbing  interest,  may  be  in  great  part 
explained.  This  condition  is  characterized  by  loss  of  volition 
and  judgment.  It  may  be  induced  in  man  and  certain  other 
animals  by  prolonged  staring  at  a  bright  object,  assisted  by  a 
concentration  of  the  attention  on  that  alone,  as  far  as  possible, 
combined  with  a  condition  of  mental  passivity  in  other  respects. 
The  individual  gradually  becomes  drowsy,  and  finally  falls  into 
a  state  in  many  respects  strongly  resembling  sleep.  With  each 
recurrence,  the  hypnotic  condition  is  usually  more  readily  in- 
duced, and  persons  have  passed  into  it  in  the  entire  absence  of 
the  usual  procedure,  having  simply  been  told  that  they  would 
be  thus  affected  at  a  given  hour.  There  is  no  special  influence 
emanating  from  peculiarly  gifted  mediums,  and  most  persons 
may  be  hypnotized  to  a  greater  or  less  degree,  though  with 
unequal  readiness. 

The  manifestations  are  very  variable,  but  are  usually  char- 
acterized by  either  total  abolition  of  certain  sensory  percep- 
tions, by  their  enfeeblement,  or  by  one  or  both  of  these,  com- 
bined possibly  with  exaltation  of  others.  Thus,  anaesthesia 
may  be  so  great  that  surgical  operations  may  be  performed 
without  consciousness  of  pain.  The  muscular  sense  may  be 
good,  so  that  the  subject  can  write  well.  He  may  smell  better 
than  usual,  so  as  to  be  able  t'c?  detect  persons  by  the  odors  from 
a  portion  of  their  clothing,  like  a  dog.  There  may  coexist,  with 
vision  for  form,  color-blindness.  These  are  to  be  regarded  mere- 
ly as  examples,  from  numberless  curious  combinations.  Again, 
the  affection  of  sense  may  be  bilateral  or  only  unilateral. 

Hypnotism  proper  may  be  combined  with  catalepsy,  a  con- 
dition in  which  the  limbs  remain  rigid  in  whatever  condition 
they  may  be  placed.  Modifications  of  the  vascular  and  respira- 
tory systems  occur.     Other  animals  have  been  hypnotized,  as 


THE  BRAIN.  529 

the  fowl,  rabbit,  Guinea-pig,  crayfish,  frog,  etc.  This  condition 
is  readily  induced  in  the  common  fowl,  more  especially  the 
wilder  individuals,  by  holding  the  creature  with  the  bill  down 
on  a  table  and  the  whole  animal  perfectly  quiet  for  a  short 
time.  Upon  the  removal  of  the  pressure  the  bird  remains  per- 
fectly passive  and  apparently  asleep  for  some  little  time. 

The  subject  of  hypnotism  and  allied  conditions  has  of  late 
received  close  attention  from  a  large  number  of  observers. 
Among  other  surprising  results  as  the  consequence  of  "  hypnotic 
suggestion,"  certain  pathological  effects  have  been  produced : 
thus,  placing  a  piece  of  tissue-paper  on  the  skin,  with  the  sug- 
gestion that  an  actual  blister  is  being  applied,  has  resulted  in 
the  usual  effects  of  such  treatment. 

Somnambulism  is  very  similar  to  hypnotism.  Individuals 
have  been  known  to  walk,  ride,  climb,  go  upon  a  journey  and 
pay  toll,  and  also  to  perform  their  ordinary  avocations.  A 
student  has  been  known  to  write  a  sermon,  read  it  over,  and 
make  corrections,  and  when  a  piece  of  pasteboard  was  placed 
before  his  eyes  this  still  went  on,  showing  that  the  images 
were  mental. 

Without  being  actually  hypnotized,  by  careful  observation 
of  one's  experiences  for  a  considerable  period,  one  may  catch, 
as  it  were,  the  realization,  at  different  times,  of  the  various 
phenomena  that  characterize  the  hypnotic  condition,  even  to 
details — though  not,  of  course,  in  that  complex  combination 
which  would  result  in  such  partial  or  complete  loss  of  conscious- 
ness as  marks  the  actual  condition ;  for  in  that  case  observa- 
tion would  be  very  difficult,  if  not  impossible.  To  illustrate  our 
meaning  briefly,  one  may  walk  a  considerable  distance,  noticing 
absolutely  nothing  consciously,  but  wholly  absorbed  in  one 
idea,  or  possibly  without  any  distinct  train  of  thought.  In  such 
a  case  there  is  neither  vision,  hearing,  nor  tactile  sensation  in 
the  ordinary  sense.  The  person  is,  in  fact,  for  the  time  practi- 
cally in  the  somnambulistic  condition  or  one  closely  allied  to  it. 
There-  are  times  when  vision'  is  in  abeyance,  or  only  one  eye 
used.  Though  ai)parently  looking,  we  do  not  see.  The  sensory 
perceptions  from  the  skin  may  be  so  purely  unilateral  that  the 
other  side  is  practically  anaesthetic  from  close  attention  to  the 
condition  of  one  side.  All  are  familiar  with  unilateral  vaso- 
motor effects,  such  as  the  redness  and  "burning"  of  one  cheek 
or  one  ear,  and  so  of  many  other  experiences  that  might  be  re- 
ferred to  did  space  permit.  Such  realizations  furnish  tlu;  highest 
kind  of  knowledge,  we  might  say  the  only  true;  knowledge. 


530 


ANIMAL   PHYSIOLOGY. 


Pathology  sheds  some  light  on  this  subject.  In  diseases  of 
the  membranes  of  the  brain,  all  the  sensory  phenomena  may- 
be so  heightened  as  to  become  painful.  Slight  sounds,  a  little 
light,  feeble  vibrations,  a  gentle  touch,  all  give  rise  to  effects 
out  of  proportion  to  the  usual  ones.  From  the  close  proximity 
of  these  membranes  to  the  cerebral  cortex,  we  may  assume  that 
they  are  affected.  This,  together  with  the  results  of  stimula- 
tion and  removal  of  the  surface  of  the  brain,  brings  us  some 
way  on  toward  an  explanation  of  sleep,  dreaming,  hibernation, 
hypnotism,  and  cerebral  localization  itself. 

One  physiologist  has  given,  as  an  explanation  of  hypnotism, 
etc.,  inhibition  of  the  cells  of  the  cerebral  cortex,  and  this,  with- 
in limits,  is  no  doubt  true.  The  facts  of  hypnotism  and  allied 
phenomena  seem  most  of  all  to  emphasize  the  dependence  of 
the  central  cells  when  acting  normally  on  afferent  impulses. 
But  we  have  already  dwelt  on  this  important  subject  suffi- 
ciently to  render  our  meaning  clear. 

Cerebeal  Localization  reconsidered. 

An  examination  of  the  phenomena  of  the  states  recently 
considered  can  leave  no  doubt  in  the  mind  that  certain  parts  of 
the  brain,  even  certain  portions  of  the  cerebrum,  may  be  active 
while  the  remaining  ones  are  in  abeyance  or  but  feebly  engaged ; 
and,  as  has  been  seen,  our  every-day  experience  is  an  illustration 
of  the  same  fact.  The  circulation  in  the  brain  points  clearly  to 
its  being  a  collection  of  organs,  with  a  certain  degree  of  inde- 
pendence. It  is  therefore  unreasonable  to  assume  that  all  parts 
of  the  cerebral  cortex  discharge  equally  the  same  functions^ 
On  the  other  hand,  it  is  just  as  unwarrantable  to  assume  that, 
in  the  face  of  all  the  facts  of  physiology  as  now  known  to  us, 
there  are  very  precisely  limited  areas  with  as  exactly  restricted 
functions  discharged  independently  of  all  the  other  parts.  As 
we  have  frequently  insisted,  the  functions  of  an  organ  are  alone 
normal  when  in  proper  relation  'to  all  the  parts  with  which  it 
is  connected — that  is,  in  fact,  with  the  entire  body.  We  learned 
that  any  conclusions  based  on  artificial  fistulse  of  the  digestive 
organs  could  be  only  approximately  correct  at  best,  and  might 
be  very  far  from  the  truth  in  the  sense  to  which  we  now  refer. 
To  assume  that  there  is  only  one  path  by  which  certain  classes 
of  impulses  must  travel  in  the  spinal  cord  has  been  shown  to  be 
unwarranted.  Therefore,  to  argue  that  because  the  removal  of 
a  certain  portion  of  the  brain  either  is  or  is  not  followed  by 


THE  BRAIN. 


531 


Fig.  3&4— Lateral  surface  of  brain  of  monkey,  displaying  motor  areas  (after  Horsley  and 
Schafer). 


F'lo.  3ft5.— Median  surface  of  brain  of  monkey  (after  Horsley  and  Schiifer). 
FijfH.  ;iHl  and  !W5  may  be  said  U>  emlwdy  the  views  of  Horsley  and  Sohiifer  more  especially, 
in  regard  to  motor  localization. 

certain  modifications  or  loss  of  function,  [)rovos  that  this  part 
is  or  is  not  concerned  with  that  particuhir  kind  of  activity,  does 
not  seem  to  be  logical. 


532 


ANIMAL  PHYSIOLOGY. 


'f^ 


THE   BRAIN. 


533 


534  ANIMAL  PHYSIOLOGY. 

If  it  be  true,  as  it  unquestionably  is,  that  a  certain  region 
of  the  cortex  or  other  portion  of  the  brain  is  normal  only  when 
in  relation  with  others,  it  follows  that  mere  removal  can  not 
entirely  solve  such  problems  as  the  function  of  the  different 
parts.  Nor  does  it  follow,  because  a  localization,  meeting  the 
needs  of  practical  medicine  and  surgery,  has  been  established, 
that  therefore  we  are  justified  in  assuming  that  a  scientific  lo- 
calization rests  upon  the  same  grounds.  Any  theory  that  fails 
to  recognize  both  the  interdependence  of  parts  and  the  resources 
of  nature  in  substituting  one  part  for  another  functionally, 
overlooks  principles  of  very  wide  application  in  biology.  We 
must  express  our  conviction  that  neither  ablation,  stimulation, 
pathological  observation,  the  results  of  surgical  interference, 
nor  the  facts  of  clinical  medicine,  can  any  of  them  singly  settle 
such  questions. 

The  comparative  method  has  been  as  yet  but  little  used. 
Conclusions  in  regard  to  the  monkey  have  been  applied  not 
only  to  man  but  other  animals ;  and  that  the  experiments  upon 
dogs  should  result  in  changes  or  the  absence  of  changes,  to 
which  there  is  no  correspondence  in  the  monkey,  has  hardly 
been  recognized  as  it  should.  It  is  only  by  the  synthetical 
method,  as  we  have  so  often  urged,  that  even  an  approximation 
to  the  truth  or  a  part  of  it  can  be  attained.  Results  from  one 
method  or  another,  taken  alone,  may  be  positively  misleading, 
unless  interpreted  in  the  light  of  many  other  facts.  The  in- 
terpretation is  the  difficult  portion  of  the  task  in  the  study  of 
localization ;  but,  before  we  are  prepared  to  formulate  a  correct 
and  comprehensive  theory,  we  must  begin  lower  in  the  animal 
scale^  extend  observations  over  a  large  number  of  animals,  and 
complete  these  by  pathological  and  clinical  observations  on 
man  and  other  mammals.  If  the  spinal  cord  becomes  func- 
tionally what  it  is  in  any  case  largely  through  the  life  experi- 
ences of  the  individual,  this  must  also  apply  to  the  brain,  hence 
we  must  look  for  individual  as  well  as  group  differences. 

The  loss  of  speech  (aphasia),  in  consequence  of  lesions  in  the 
left  third  frontal  convolution,  was  formerly  pointed  to  as  un- 
doubted evidence  of  localization ;  but,  the  more  this  subject  has 
been  studied,  the  more  clearly  it  has  been  perceived  that  even 
in  this  case  the  theories  of  a  rigid  localization  break  down. 

The  speech-center  has  had  its  boundaries  extended ;  and  it 
turns  out  that  a  vast  complex  of  connections  must  be  consid- 
ered, many  of  which  are  not  confined  to  the  third  frontal  con- 
volution or  its  neighborhood. 


THE   BRAIN.  535 

There  is  a  kind  of  experimental  evidence  that  throws  a  good 
deal  of  light  on  the  present  discussion.  It  is  found  that,  when 
certain  drugs  have  been  administered,  the  irritability  of  the 
cortex  is  either  increased  or  diminished,  according  to  the  stage 
of  action  of  the  drug  (morphia,  etc.).  It  is  not  impossible 
that  epileptiform  convulsions  may  result  from  the  application 
of  a  stimulus  of  almost  any  strength,  though  this  result  does 
not  follow  when  the  electrodes  are  applied  to  the  underlying 
white  substance.  The  disease  epilepsy  has  been  known  to  fol- 
low injuries  to  the  cranium  or  the  brain  membranes,  in  conse- 
quence of  which  the  cells  themselves  of  the  cortex  have  been 
altered  in  function.  Moreover,  the  epileptiform  movements 
may  be  in  such  cases  confined  to  certain  muscles,  thus  pointing 
to  a  motor  localization.  If  a  muscle  contraction,  as  the  result 
of  stimulation  of  a  motor  area  (the  animal  being  under  the  in- 
fluence of  morphia),  be  recorded  by  the  graphic  method,  and  the 
sciatic  nerve  then  divided,  in  repeating  the  original  experiment, 
it  will  be  seen  that  the  whole  character  of  the  curve  is  altered, 
the  latent  period  having  been  lengthened,  and  the  height  of 
the  curve  lessened.  This  points  to  an  inhibitory  influence  exer- 
cised over  the  cortical  motor  cells,  by  afferent  influences,  and  we 
are  at  once  reminded  of  Schiff 's  theory ;  but  most  of  all  do  such 
experiments  enforce  that  close  relationship  of  all  parts  of  the 
body  which  finds  its  reflection  in  the  brain  cortex  as  elsewhere. 

We  have  dwelt  upon  the  subject  of  cerebral  localization  at 
length,  because  of  its  great  practical  and  scientific  importance, 
not  alone  for  medicine  and  physiology,  but  in  the  allied  depart- 
ment of  psychology.  In  conclusion,  we  may  express  the  view 
that  there  is  in  the  cerebral  cortex  a  localization  of  function, 
variable  for  each  group  of  animals,  and  to  some  extent  for 
each  individual ;  that  it  is  not  of  a  character  to  be  mapped  out 
by  mathematical  lines ;  that  in  case  of  disease  or  injury  one 
part  may  to  a  certain  extent  take  up  the  functions- of  another ; 
that  the  functions  of  any  part,  however  limited,  are  only  to  be 
understood  when  taken  in  connection  with  all  other  parts  of 
the  cortex,  of  the  brain,  and,  in  fact,  of  the  entire  body.  These 
views  we  believe  to  be  borne  out  by  tlie  facts  of  physiological 
experiment,  clinical  medicine,  operative  surgery,  pathology, 
sleep,  dreaming,  hypnotism,  the  nature  of  the  cerebral  circu- 
lation, and  llio  g(in(;ral  ti'uths  of  lji(^logy. 

Cerebral  Time. — We  have  alr(;ady  considered  cerebral  reflex 
time,  and  now  proceed  to  examine  into  the  period  occupied  by 
a  mental  operation  involving  attention  and  volition. 


536  ANIMAL  PHYSIOLOGY. 

When  a  subject  makes  some  signal  in  response  to  a  stimu- 
lus, we  recognize  three  parts  to  the  entire  chain  of  events :  1. 
The  time  occupied  in  the  passage  of  the  afferent  impulses  in- 
ward along  certain  lengths  of  nerve  from  a  peripheral  sense- 
organ.  2.  The  time  taken  up  by  the  processes  of  the  central 
cells  before  the  efferent  nervous  discharge  takes  place.  3.  The 
time  consumed  by  the  passage  of  the  efferent  impulses  from 
the  center  to  the  muscle  involved.  The  whole  interval  is  termed 
the  reaction-time,  while  the  second  constitutes  the  reduced  re- 
action-time. 

As  the  first  and  third  probably  vary  but  little,  it  is  highly 
probable  that  the  difference  in  the  reaction-time  observable  in 
different  individuals,  and  very  much  modified  by  the  condition 
at  the  moment  (as  fatigue),  and  especially  by  practice,  is  trace- 
able to  the  central  cells.  In  popular  language,  some  persons 
are,  as  compared  with  others,  slow  thinkers.  This  factor  is  the 
"personal  equation,"  so  called.  There  are,  of  course,  many 
sources  of  error  in  such  calculations,  but  approximate  results 
of  value  may  be  reached.  It  would  appear  that  the  reaction 
period  for  tactile  is  shorter  than  for  visual  or  auditory  sensa- 
tions, while  that  of  vision  is  longer  than  for  hearing.  The 
respective  periods  have  been  set  down  as  about  ^  of  a  second 
for  vision,  ^  for  audition,  and  \  for  feeling. 

The  central  processes  may  be  reckoned  to  take  (for  percep- 
tion and  volition)  about  yV  of  ^  second. 

If  discriminations  have  to  be  made — so  as  to  decide,  e.  g., 
whether  it  is  the  right  or  the  left  side  of  the  body  that  has 
been  touched — a  longer  time  is,  of  course,  required,  and  the  re- 
action period  in  this  case  also  varies  greatly.  It  has  been  set 
down  as  occupying  from  gV  to  -|-  of  a  second.  From  these  con- 
siderations, it  will  be  plain  that  "  the  lightning-like  rapidity 
of  thought "  is  a  rather  extravagant  figure  of  speech. 

Functions  of  other  Portions  of  the  Brain. 

Certain  parts  of  the  encephalon  are  spoken  of  as  the  basal 
ganglia,  prominent  among  which  are  the  corpus  striatum  and 
the  optic  thalamus. 

The  Corpus  Striatum  and  the  Optic  Thalamus.— The  corpus 
striatum  consists  of  several  parts,  the  main  divisions  being  an 
intra-ventricular  portion  or  caudate  nucleus,  and  an  extra- 
ventricular  part  or  lenticular  nucleus. 

Between  these  lies   the  internal    capsule,  through  which 


THE   BRAIN. 


537 


pass  fibers  that  spread  out  toward  tlie  cortex,  as  the  corona 
radiata. 


Fig.  388.— Transverse  section  of  cerebral  hemispheres,  at  level  of  cerebral  ffanslia  (after 
Daltoni.  1.  Kreat  longitudinal  fissure  :  2,  part  of  same  between  occipital  1<i1m-s  ;  3,  anterior 
part  of  corpus  callosum  ;  4,  fissure  of  Sylvius  ;  5,  convolutions  of  island  nf  l{i-il  (insula^;  6, 
caudate  nucleus  of  corpus  striatum;  7,  lenticular  nucleus  of  corpus  striatum;  8,  optic 
thalamus  ;  9,  internal  capsule  ;  10,  external  capsule  ;  11,  claustruni. 

Pathology,  especially,  has  shown  that  a  lesion  of  the  intra- 
ventricular portion  of  the  corpus  striatum,  and,  above  all,  of 
the  internal  capsule,  is  followed  by  failure  of  voluntary  move- 
ment (akinesia).  It  would  appear  that  a  great  part  of  the 
fibers  from  the  motor  area  around  the  fissure  of  Rolando,  pass 
through  the  intra-ventricular  parts  of  the  corpus  striatum,  and 
especially  its  internal  capsule.  But  it  is  also  to  be  borne  in 
mind  that  a  large  part  of  the  fibers  passing  from  the  cortex 
make  connection  with  the  cells  of  the  corpus  striatum  before 
reaching  the  cord.  These  facts  render  the  occurrence  of  loss  of 
voluntary  motor  power  comprehensible. 

The  fibers  of  tin-  peduncles  of  the  brain  may  be  divided  into 


538 


ANIMAL  PHYSIOLOGY. 


an  interior  or  lower  division  (crusta),  going  mostly  to  the  cor- 
pus striatum,  and  a  posterior  division  {tegmentum),  passing 
principally  to  the  optic  thalmi ;  many,  possibly  most  of  them, 
ultimately  reach  the  cortex.  Many  clinical  observers  do  not 
hesitate  to  speak  of  the  optic  thalamus  as  sensory,  in  function 
and  the  corpus  striatum  as  motor ;  but  the  clinical  and  patho- 


FiG.  389.— Transverse  section  of  human  brain  (after  Dalton).  This  and  the  preceding  figure 
are  somewhat  diagrammatic.  1,  pons  Varolii ;  2,  2,  crura  cerebri ;  3,  3,  internal  capsule  ; 
4,  4,  corona  radiata  ;  5,  optic  thalamus  ;  6,  lenticular  nucleus  ;  7,  corpus  callosum. 

logical  evidence  is  conflicting — all  lesions  of  these  parts  not 
being  followed  by  loss  of  sensation  and  motion  respectively ; 
though  an  injury  to  the  internal  capsule  generally  results  in 
paralysis.  All  are  agreed  that  the  symptoms  are  manifested 
on  the  side  of  the  body  opposite  to  the  side  of  the  lesion,  so 
that  a  decussation  must  take  place  somewhere  between  the 
ganglion  and  the  periphery  of  the  body. 

There  is  no  doubt  that  the  optic  thalamus,  especially  its 
posterior  part,  is  concerned  with  vision,  for  injury  to  it  is  fol- 
lowed by  a  greater  or  less  degree  of  disturbance  of  this  func- 
tion. As  has  been  already  pointed  out,  unilateral  injury  of 
either  of  these  ganglia  leads  to  inco-ordination  or  to  forced 
movements.  That  these  regions  act  some  intermediate  part  in 
the  transmission  of  impulses  to  and  from  the  brain  cortex,  and 
that  the  anterior  one  is  concerned  with  motor,  and  the  pos- 
terior possibly  with  sensory  (tactile,  etc.),  and  certainly  with 
visual  impulses,  may  be  stated  with  some  confidence,  though 
further  details  are  not  yet  a  subject  of  general  agreement. 


THE   BRAIX. 


539 


Corpora  auadrigemina.— The  function  of  these  parts  in  vision, 
as  in  the  co-ordination  of  the  movements  of  the  ocular  muscles, 


Fig 


tion  of  spinal  cord 

fil)erH  ;  c.  c,  commissural  fibers. 

and  tlioir  relations  to  the  movements  of  the  pupil,  will  be 
considered  later.  However,  the  actual  centers  for  these  func- 
tions s('f;m  to  lie  in  the  anterior  portion  of  the  floor  of  the 
a^ineduct  of  Sylvius,  and  are  indirectly  alfccded  by  stimulation 
of  the  corpora  quadrigemina.     Extirpation  of  these  parts  on 


540  ANIMAL  PHYSIOLOGY. 

one  side  produces  blindness  of  the  opposite  eye,  and  in  birds, 
etc.,  the  same  result  follows  when  their  homolognes — the  optic 
lobes — are  similarly  treated.  There  can  be  no  doubt,  therefore, 
that  they  are  a  part  of  the  central  nervous  machinery  of  vision, 
and  it  seems  to  be  probable  that  the  anterior  parts  of  the  cor- 
pora quadrigemina  alone  have  this  visual  function.  But,  since 
it  is  the  opposite  eye  that  is  affected,  and  in  some  animals 
(rabbits)  that  alone,  we  are  led  to  infer  a  decussation  of  the 
optic  fibers,  or  at  least  of  impulses.  In  dogs,  on  the  other  hand, 
the  crossing  seems  to  be  but  partial.  From  the  fact  that  only 
a  part  of  the  visual  field  is  wanting  (hemianopsia — i.  e.,  that 
only  the  half  of  the  usual  field  of  view  is  visible),  and,  since 
there  may  be  hemianopsia  of  both  eyes,  with  unilateral  disease 
of  the  brain,  it  has  been  inferred  that  in  man  the  decussation 
is  also  incomplete.  We  may  remark  incidentally  that  it  has 
lately  been  maintained  that  removal  of  one  occipital  lobe  in  the 
monkey  leads  to  heminopsia  of  the  opposite  eye.  These  parts, 
as  we  have  already  seen,  take  some  share  in  the  co-ordination  of 
muscular  movements,  and  give  rise  to  forced  movements  after 
unilateral  injury. 

It  begins  to  appear  that  there  are  several  parts  of  the  brain 
concerned  with  vision.  After  removal  of  almost  any  part  of 
the  cerebral  cortex,  if  of  sufficient  extent,  vision  is  impaired. 
We  may  say,  then,  that,  before  an  object  is  "  seen"  in  the  high- 
est sense,  processes  beginning  in  the  retina  undergo  further 
elaboration  in  the  corpora  quadrigemina,  optic  thalami,  and, 
finally,  in  the  cerebral  cortex.  We  may  safely  assume  that  the 
part  played  by  the  latter  is  of  very  great  importance,  making 
the  perception  assume  that  highest  completeness  which  is  of 
very  varying  character,  no  doubt,  with  different  groups  of 
animals.  In  a  sense,  all  mammals  may  see  alike,  and,  in  an- 
other sense,  they  may  see  things  very  differently ;  for,  if  we 
may  judge  by  the  differences  in  this  respect  between  educated 
and  uneducated  men,  the  great  dissimilarity  lies  in  the  inter- 
pretation of  what  is  seen ;  in  a  word,  the  cortex  has  to  do  with 
the  perfecting  of  visual  impulses.  Nevertheless,  a  break  any- 
where in  the  long  and  complicated  chain  of  processes  must  lead 
to  some  serious  impairment  of  vision.  Much  of  the  same  sort 
of  reasoning  applies  to  the  other  senses  and  also  to  speech. 

To  speak,  therefore,  of  a  visual  center  or  a  speech  center  in 
any  very  restricted  sense  is  unjustifiable ;  at  the  same  time,  it 
is  becoming  clearer  that  there  is  in  the  occipital  lobe,  rather 
than  in  other  parts  of  the  cortex,  an  area  which  takes  a  pecul- 


THE   BRAIN.  541 

iar  and  special  share  in  elaborating  visual  impulses  into  visual 
sensations  and  perceptions ;  and  there  can  be  little  doubt 
that  the  other  senses  are  represented  similarly  in  the  cerebral 
cortex. 

The  Cerebellum.  —  Both  physiological  and  pathological  re- 
search point  to  the  conclusion  that  the  cerebellum  has  an  im- 
portant share  in  the  co-ordination  of  muscular  movements. 
Ablation  of  parts  of  the  organ  leads  to  disordered  movements ; 
and,  when  the  whole  is  removed  in  the  bird,  co-ordination  is 
all  but  impossible,  and  the  same  holds  for  mammals.  Section 
of  the  middle  peduncle  of  one  side  is  liable  to  give  rise  to  roll- 
ing forced  movements.  In  fact,  injury  to  the  cerebellum  causes 
symptoms  very  similar  to  those  following  section  of  the  semi- 
circular canals,  so  that  many  have  thought  that  in  the  latter 
case  the  cerebellum  had  itself  been  injured. 

Pathological. — Tumors  and  other  lesions  frequently,  though 
not  invariably,  give  rise  to  unsteadiness  of  gait,  much  like  that 
atfecting  an  intoxicated  person.  It  may  safely  be  said  that  the 
cerebellum  takes  a  very  prominent  share  in  the  work  of  the 
muscular  co-ordination  of  the  body. 

As  has  already  been  pointed  out,  several  tracts  of  the  spinal 
cord  make  connection  with  the  cerebellum,  and  it  is  not  to  be 
forgotten  that  this  part  of  the  brain  has,  in  general,  most  ex- 
tensive connections  with  other  regions.  Insufficient  study  has 
as  yet  been  given  to  the  cerebellum,  and  it  is  likely  that  the 
part  it  takes  in  the  functions  of  the  encephalon  is  greater  than 
has  yet  been  rendered  clear.  The  old  notion  that  this  organ 
bears  any  direct  relation  to  the  sexual  functions  seems  to  be 
without  foundation.  It  has  now  been  clearly  demonstrated 
that  the  lower  region  of  the  spinal  cord  is,  in  the  dog  and  prob- 
ably most  mammals,  the  part  of  the  nerve-centers  essential  for 
the  sexual  processes. 

Crura  Cerebri  and  Pons  Varolii. — As  has  been  already  noted, 
the  peduncles  (crura)  are  the  paths  of  impulses  from  certain 
parts  of  the  cereln-al  cortex,  the  basal  ganglia,  and  the  spinal 
cord.  The  functions  of  the  gray  matter  of  the  crura  are  un- 
known. But,  since  forced  movements  ensue  on  unilateral  sec- 
tion, it  is  f)lain  that  they  also  have  to  do  with  muscular  co- 
ordination. 

Tlie  transverse  fibers  of  the  pons  Varolii  connect  tljo  two 
halves  of  the  cerebellum.  Its  longitudinal  fibers  have  extensive 
connections — the  anterior  pyramids  and  olivary  bodies  of  the 
medulla,  the  lateral,  and  perhaps  also  a  part  of  the  posterior 


542  ANIMAL   PHYSIOLOGY. 

columns  of  the  cord,  while  upward  these  fibers  connect  with 
the  crura  cerebri  and  so  with  the  cortex. 

Pathological, — Paralysis  of  the  face  usually  occurs  on  the 
same  side  as  that  of  the  rest  of  the  body ;  hence  it  must  be 
inferred  that  there  is  a  decussation  somewhere  of  the  fibers  of 
the  facial  nerve ;  but  there  is  much  still  to  be  learned  about  this 
subject. 

Medulla  Oblongata. — In  some  animals  (frogs)  it  is  certainly 
known  that  this  region  of  the  brain  has  a  co-ordinating  func- 
tion, and  it  is  probable  that  it  is  concerned  with  such  uses  in 
all  animals  that  possess  the  organ,  or  rather  collection  of  organs, 
seeing  that  this  part  of  the  brain  must  be  regarded  as  especially 
a  mass  of  centers,  the  functions  of  which  have  been  already 
considered  at  length.  So  long  as  the  medulla  is  intact^  life  may 
continue ;  but,  except  under  special  circumstances,  which  do 
not  invalidate  this  general  statement,  its  destruction  is  followed 
by  the  death  of  the  animal. 

We  may  simply  enumerate  the  centers  that  are  usually 
located  in  the  medulla :  The  respiratory  (and  convulsive),  car- 
dio-inhibitory,  vaso-motor,  center  for  deglutition,  center  for 
the  movements  of  the  gullet,  stomach,  etc.,  and  the  vomiting 
center ;  center  for  the  secretion  of  saliva  and  possibly  other  of 
the  digestive  fluids.     Some  add  a  diabetic  and  other  centers. 

Special  Considerations. 

Embryological. — The  further  we  progress  in  the  study  of  the 
nervous  system,  the  greater  the  significance  of  the  facts  of  its 
early  development  becomes.  It  will  be  remembered  that  from 
that  uppermost  epiblastic  layer  of  cells  so  early  marked  off  in 
the  blastoderm,  is  formed  the  entire  nervous  system,  including 
centers,  nerves,  and  end  organs.     The  brain  may  be  regarded 


l^^G.  391.— Vertical  longitudinal  section  of  brain  of  human  embryo  of  fourteen  weeks.  1x8. 
(After  Sharpey  and  Reichert.)  c,  cerebral  hemisphere  ;  cc,  corpus  callosum  beginning  to 
pass  back  ;  /,  foramen  of  Munro  ;  p,  membrane  over  third  ventricle  and  the  pineal  body  ; 
th.  thalamus  ;  3,  third  ventricle  ;  /,  olfactory  bulb  ;  eg,  corpora  quadrigemina  ;  cr,  crura 
cerebri,  and  above  them,  aqueduct  of  Sylvius,  still  wide  ;  c',  cerebellum,  and  below  it  the 
fourth  ventricle  ;  pv^  pons  Varolii ;  m,  medulla  oblongata. 


THE   BRAIN. 


543 


as  a  specially  differentiated  part  of  the  anterior  region  of  the 
medullary  groove  and  its  subdivisions ;  and  the  close  relation 
of  the  eye,  ear,  etc.,  to  the  brain  in  their  early  origin,  is  not 
without  special  meaning,  while  the  more  diffused  sensory  de- 
velopments in  the  skin  connect  the  higher  animals  closely  with 
the  lower — even  the  lowest,  in  which  sensation  is  almost  wholly 
referable  to  the  surface  of  the  body. 


Fig.  392, 


Fig.  39.3. 

Fig.  392.— <")uter  surface  of  human  foetal  brain  at  six  months,  showing  origin  of  principal 
fissures  (after  Sharpey  and  R.  Wagner).  F,  frontal  lobe  ;  P,  parietal ;  O.  occipital ;  T, 
temporal :  o.  a.  a.  faint  appearance  of  several  frontal  convolutions  ;  s,  .s,  sylvian  fissure  ; 
s',  anterior  divi.sion  of  same  ;  C.  central  lobe  of  island  of  ReU  ;  r,  fissure  of  Rolando  ;  p, 
external  perpendicular  fissure. 

Fig.  393.— Upper  surface  of  brain  represented  in  Fig.  OoO  (after  Sharpey  and  R.  Wagner). 


Without  some  knowledge  of  the  mode  of  development  of 
the  encephalon^  it  is  scarcely  possible  to  appreciate  that  rising 
grade  of  complexity  met  with  as  we  pass  from  lower  to  higher 
groups  of  animals,  especially  noticeable  in  vertebrates ;  nor  is 
it  possible  to  recognize  fully  the  evidence  found  in  the  nervous 
system  for  the  doctrine  that  higher  are  derived  from  lower 
forms  by  a  process  of  evolution. 

Evolution. — The  same  law  applies  to  the  nervous  system  as 
to  other  parts  of  the  organism,  viz.,  that  the  individual  devel- 
opment (ontogeny)  is  a  synoptical  representation,  in  a  general 
way,  of  the  development  of  the  group  (phylogeny).  A  com- 
parison of  the  development  of  even  man's  brain  reveals  the  fact 
that,  in  its  earliest  stage,  it  is  scarcely,  if  at  all,  distinguishable 
from  that  of  any  of  the  lower  vertebrates.  There  is  a  period 
when  even  this,  the  most  convoluted  of  all  brains,  is  as  smooth 
and  dev<jid  of  gyri  as  the  brain  of  a  frog.  The  extreme  com- 
plexity of  the  human  brain  is  referable  to  excessive  growth  of 


544 


ANIMAL  PHYSIOLOGY. 


certain  parts,  crowding  and  alteration  of  shape,  owing  to  tlie 
influence  of  its  bony  case,  its  membranes,  etc. 


Fig.  394.— a,  brain  of  aye-aye  (Lemur) ;  B,  of  marmoset ;  C,  of  squirrel-monkey  (Callithrix) ; 
D.  of  macaque  monkey ;  E,  of  gibbon  ;  F,  of  a  fifth-month  human  foetus  (after  Owen). 
Although  naturalists  are  agreed  that  the  monkeys,  apes,  and  lemurs  are  related,  consider- 
able differences  are  to  be  observed  in  their  brains.  These  figures  also  illustrate  the  remark 
made  after  the  following  ones. 

It  is  evident,  from  an  inspection  of  the  cranial  cavities  of 
those  enormous  fossil  forms  that  preceded  the  higher  verte- 
brates, that  their  brains,  in  proportion  to  their  bodies,  were 
very  small,  so  that  any  variation  in  the  direction  of  increase 
in  the  encephalon — especially  the  cerebrum — must  have  given 
the  creatures,  the  subject  of  such  variation,  a  decided  advan- 
tage in  the  struggle  for  existence,  and  one  which  may  partly 
account,  perhaps,  for  the  extinction  of  those  animals  of  vast 
proportions  but  limited  intelligence.    That  the  size  of  the  brain 


Fig.  395. — A,  brain  of  a  chelonian ;  B,  of  a  foetal  calf ;  C,  of  a  cat.  (All  after  Gegenbaur.) 
I  indicates  cerebral  hemispheres ;  II,  thalamus :  ///,  corpora  quadrigemina ;  IV,  cerebel- 
lum ;  V,  medulla  ;  st,  corpus  striatum  ;  /,  fornix  ;  h,  hippocampus  ;  sr,  fourth  ventricle  ; 
a,  geniculate  body  ;  ol,  olfactory  lobe.  It  will  be  observed  (1)  how  the  foetal  brain  in  a 
higher  animal  form  resembles  the  developed  brain  in  a  lower  form,  and  (2)  how  certain 
parts  become  crowded  together  and  covered  over  by  more  prominent  regions,  e.  g.,  the 
cerebrum,  as  we  ascend  the  animal  scale. 


THE   BRAIN. 


545 


as  well  as  its  quality  can  be  increased  by  use,  seems  to  have 
been  established  by  the  measurements,  at  different  periods  of 
development,  of  the  heads  of  those  engaged  in  intellectual  pur- 
suits, and  comx^aring  the  results  with  those  obtained  by  similar 
measurement  of  the  heads  of  those  not  thus  specially  employed. 
Of  course,  it  must  be  assumed  that  the  head  measurement  is  a 
gauge  of  the  size  of  the  brain,  which  is  approximately  true,  if 


Fig.  396. 


Fig.  397. 


Fig.  396.— Brain  of  cat,  seen  from  above  (after  Tiedemann). 
Fig.  397.— Brain  of  dog,  seen  from  above  (after  Tiedemann). 

not  entirely  so.  There  are  many  facts  which  go  to  show  that 
the  habits  of  ancestors  tend  to  become  almost  the  instincts  of 
posterity,  even  in  the  case  of  man.  It  has  been  noticed  that  a 
facility  in  the  acquisition  of  scholarship  (languages,  literature) 
has,  in  many  cases,  been  associated  with  scholarly  habits  in 
numerous  generations  of  ancestors.  The  inheritance  of  mental 
traits,  which  can  not  be  considered  wholly  apart  from  a  physi- 
cal basis  in  the  nervous  system,  and  especially  in  the  cerebrum, 
is  a  subject  of  great  interest,  but  too  wide  for  more  than  a  j^ass- 
ing  allusion  here. 

Recent  investigations  seem  to  show  that  the  development 
of  the  ganglion  cells  of  the  brain  takes  place  first  in  the  me- 
dulla, next  in  the  cerebellum,  after  that  in  the  mid-brain,  and 
finally  in  the  cerebral  cortex.  Animals  most  helpless  at  birth 
are  those  with  the  least  development  of  such  cells.  The  me- 
dulla may  be  regarded  in  some  sense  as  the  oldest  (phylogeneti- 
cally)  part  of  the  brain.  In  it  are  lodged  those  cells  (centers) 
which  are  required  for  the  maintenance  of  the  functions  essen- 
tial to  somatic  lift;.  This  may  serve  to  explain  hf)W  it  is  that 
Ko  many  centers  are  there  crowded  tog(jtlier.  It  is  rcmai-kable 
that  80  small  a  part  of  the  brain  should  preside  over  many  im- 
yorUiui  functions;  but  the  principle  of  cfmcentration  witli  pro- 
gressive development,  and  the  law  oi  haliit  making  automatism 
'a, 


546  ANIMAL  PHYSIOLOGY. 

prominent^  throw  some  light  upon  these  facts,  and  especially 
the  one  otherwise  not  easy  to  understand,  that  so  much  impor- 
tant work  should  be  done  by  relatively  so  few  cells.  Possibly, 
however,  if  localization  is  established  as  fully  as  it  may  eventu- 
ally be,  this  also  will  not  be  so  astonishing, 

Nevertheless,  the  doctrine  that  so  small  a  region  of  the 
medulla  as  is  the  vaso-motor  center,  for  example,  should  con- 
trol so  many  different  vascular  tracts,  ought  not  to  be  finally 
accepted  without  close  examination.  It  is  so  easy  to  speak  of  a 
"  center  "  for  any  function  and  to  locate  it  in  the  medulla ;  but 
it  is  not  unlikely  that  the  physiology  of  the  future  will  greatly 
modify  our  present  teaching  in  this  regard.  As  in  many  other 
cases,  the  explanations  seem  to  be  too  simple  and  too  artificial. 

The  law  of  habit  has,  in  connection  with  our  psychic  life 
and  that  of  other  mammals,  some  of  its  most  striking  develop- 
ments. This  has  long  been  recognized,  though  that  the  same 
law  is  of  universal  application  to  the  functions  of  the  body  has 
as  yet  received  but  the  scantiest  acknowledgment. 

We  shall  not  dwell  upon  the  subject  beyond  stating  that  in 
our  opinion  the  psychic  life  of  animals  can  be  but  indifferently 
understood  unless  this  great  factor  is  taken  into  the  account ; 
and  when  it  is,  much  that  is  apparently  quite  inexplicable  be- 
comes plain.  That  anything  that  has  happened  once  any- 
where in  the  vital  economy  is  liable  to  repetition  under  a 
slighter  stimulus,  is  a  law  of  the  utmost  importance  in  physiol- 
ogy, psychology,  and  pathology.  The  practical  importance  of 
this,  especially  to  the  young  animal,  is  of  the  highest  kind. 

The  doctrine  of  a  "  cortical  projection  "  for  the  senses,  or 
cortical  sense-centers,  has  enough  foundation  to  enable  us  to 
draw  certain  inferences  relative  to  the  direction  to  be  given  to 
the  education  of  youth.  If  true,  then  the  education  of  the 
senses  has  a  thoroughly  good  foundation  in  physiology,  and 
"  manual  training "  should  receive  the  hearty  support  of  sci- 
entists. It  follows  that  in  developing  the  senses  we  are  devel- 
oping the  most  important  part  of  the  brain  for  all  higher  ends, 
the  cerebral  cortex. 

It  will  now  also  be  clear  that  if  there  are  cortical  motor  re- 
gions, then  the  size  of  the  cerebrum  and  the  muscular  develop- 
ment may  stand  in  a  closer  relation  than  we  have  been  wont  to 
believe.  That  connection  of  the  muscular  sense,  tactile  sensi- 
bility, sight,  etc.,  aimed  at  in  "  manual  training,"  is  in  harmony 
with  what  we  have  frequently  urged  in  relation  to  the  mutual 
dependence  of  one  part  of  the  brain  upon  another.     Both  theo- 


THE   BRAIN.  547 

retically  and  practically  it  is  important  to  recognize  that  the 
value  of  vision,  indeed,  the  extent  to  which  we  "  see,"  is  in  no 
small  degree  related  to  what  we  feel.  The  carpenter  judges  dis- 
tances well  by  his  eye,  because  he  is  constantly  correcting  his 
visual  judgments  by  his  tactile  sense,  his  muscular  sense,  etc. 

We  must  point  out,  however,  that  the  special  developments 
of  disease  at  the  present  day  point  to  the  dangers  of  an  undue 
use  or  development  of  the  cerebrum.  That  balance  indispen- 
sable for  health  must  be  preserved,  if  the  race  is  to  avoid  degen- 
eration. 

Synoptical. — There  is  as  yet  no  systematized  clear  physiology 
of  "  the  brain."  We  are  conversant  with  certain  phenomena 
referable  to  this  organ  in  a  number  of  animals,  chiefly  the 
higher  mammals ;  but  our  knowledge  is  as  yet  insufficient  to 
generalize,  except  in  the  broadest  way,  regarding  the  functions 
of  the  brain — i.  e.,  to  determine  what  is  common  to  the  brains  of 
all  vertebrates  and  what  is  peculiar  to  each  group.  Referring, 
then,  to  the  higher  mammals,  especially  to  the  dog,  the  cat,  the 
monkey,  and  man,  we  may  make  the  following  statements : 

The  medulla  oblongata  is  functionally  the  ruler  of  vegeta- 
tive life — the  lower  functions ;  and  so  may  be  regarded  as  the 
seat  of  a  great  number  of  "  centers,"  or  collections  of  cells  with 
functions  to  a  large  degree  distinct,  but  like  close  neighbors, 
with  a  mutual  dependence. 

Phylogenetically  (ancestrally)  the  medulla  is  a  very  ancient 
region,  hence  the  explanation  apparently  of  so  many  of  its 
functions  being  common  to  the  whole  vertebrate  group. 

Parts  of  the  mesencephalon,  the  pons  Varolii,  the  optic  lobes 
or  corpora  quadrigemina,  the  crura  cerebri,  etc.,  are  not  only 
connecting  paths  between  the  cord  and  cerebrum,  but  seem  to 
preside  over  the  co-ordination  of  muscular  movements,  and  to 
take  some  share  in  the  elaboration  of  visual  and  perhaps  other 
sensory  impulses. 

The  cerebellum  may  have  many  functions  unknown  to  us. 
Its  connections  with  other  parts  of  the  nerve-centers  are  numer- 
ous, though  their  significance  is  in  great  part  unknown.  Both 
Ijathological  and  jdiysiological  investigation  point  to  its  hav- 
ing a  large  share  in  muscular  co-ordination. 

It  is  certain  that  the  cerebrum  is  the  part  of  the  brain  essen- 
tial for  all  the  higher  psychic  manifestations  in  the  most  ad- 
vanc<;d  mammals  and  in  man. 

The  preponderating  development  of  man's  cerebrum  ex- 
plains at  once  liis  domination  in  the  animal  world,  his  ])0wer 


548 


ANIMAL  PHYSIOLOGY. 


over  the  inanimate  forces  of  JSTature  and  his  peculiar  infirmities, 
tendencies  to  a  certain  class  of  diseases,  etc. — in  a  word,  man  is 
man,  largely  by  virtue  of  the  size  and  peculiarities  of  this  part 
of  his  brain. 

Modern  research  has  made  it  clear  also  that  there  is  a  "  pro- 
jection "  of  sensory  and  motor  phenomena  in  the  cerebral  cor- 
tex ;  in  other  words,  that  there  are  sensory  and  motor  centers 
in  the  sense  that  in  the  cortex  there  are  certain  cells  which  have 
an  important  share  in  the  initiation  of  motor  impulses,  and  oth- 
ers employed  in  the  final  elaboration  of  sensory  ones. 

It  is  even  yet  premature  to  dogmatize  in  regard  to  the  site 
of  these  centers ;  especially  are  we  not  ready  for  large  generali- 
zations. In  man  the  convolutions  around  the  fissure  of  Rolando 
constitute  the  motor  area  best  determined. 

The  whole  subject  of  cortical  localization  requires  much  ad- 
ditional study,  especially  by  the  comparative  method  in  the 
widest  sense — i.  e.,  by  a  comparison  of  the  results  of  operative 
procedure  in  a  variety  of  groups  of  animals,  and  the  results  of 
clinical,  pathological,  physiological,  and  psychological  investi- 
gation. Especially  must  allowance  be  made  for  differences  to 
be  observed,  both  for  the  group  and  the  individual ;  and  also 
for  the  influence  which  one  region  exerts  over  another.  Be- 
tween the  weight  of  the  cerebrum,  the  extent  of  its  cortical 
surface,  and  psychic  power,  there  is  a  general  relationship. 


GENERAL   REMARKS  ON  THE  SENSES. 

Our  studies  in  embryology  have  taught  us  that  all  the  vari- 
ous forms  of  end-organs  are  developed  from  the  epiblast,  and 


Fig.  398. — Papillae  of  skin  of  palm  of  hand  (after  Sappey).    A  vascular  network  in  all  cases, 
and  in  some  nerves  and  tactile  coi-puscles,  enter  the  papiUse. 


GENERAL   REMARKS  ON  THE  SENSES. 


549 


so  may  be  regarded  as  modified  epithelial  cells,  with  which  are 
associated  a  vascular  and  nervous  supply.  These  end-organs 
are  at  once  protective  to  the  deli- 
cate nerves  which  terminate  in 
them,  and  serve  to  convey  to  the 
latter  peculiar  impressions  which 
are  widely  different  in  most  in- 
stances from  those  resulting  from 
the  direct  contact  of  the  nerve  with 
the  foreign  body.  All  are  ac- 
quainted with  the  fact  that,  when 


^^=^-% 


s'^-i|- 


Fir..  399. 


Fig.  400. 


Fig.  399.— Corpuscle  of  Vater  (after  Sappey). 

Fio.  400.— End-bulbs  (corpuscles)  of  Krause  (after  Ludden).     A,  from  conjunctiva  of  man  ; 

B,  from  conjunctiva  of  calf.    It  may  be  noticed  that  in  all  these  cases  the  nerve  loses  its 

non-essential  parts  before  entering  the  corpuscle. 

the  epithelium  is  removed,  as  by  a  blister,  we  no  longer  possess 
tactile  sensibility  of  the  usual  kind,  and  experience  pain  on 
contact  with  objects ;  in  a  word,  the  series  of  connections  neces- 
.sary  to  a  sense-perception  is  broken  at  the  commencement. 

Seeing  that  all  the  end-organs  on  the  surface  of  the  body 
have  a  common  origin  morphologically,  it  would  be  reasonable 
to  expect  that  the  senses  would  have  much  in  common,  espe- 
cially when  these  organs  are  all  alike  connected  with  central 
nervous  cells  by  nerves.  As  a  matter  of  fact,  such  is  the  case, 
and  in  every  instance  we  can  distinguish  between  sensory  im- 
jjulses  generated  in  the  end-organ,  conveyed  by  a  nerve  inward, 
and  those  in  the  cells  of  these  central  nervous  systems,  giving 


550 


ANIMAL   PHYSIOLOGY. 


Fig.  401.— Nerves  with  ganglion  cells  (G)  beneath  a 
tactile  bristle  (Tb),  from  skin  of  an  arthropod 
ICorethra)  larva. 


rise  to  certain  molecular  changes  which  enable  the  mind  or 
the  ego  to  have  a  perception  proper ;  which,  when  taken  in  con- 
nection with  numerous  past 
experiences  of  this  and 
other  senses,  furnishes  the 
material  for  a  sensory  judg- 
ment. 

The  chief  events  are, 
after  all,  internal,  and  hence 
it  is  found  that  the  higher 
in  the  scale  the  animal 
ranks,  the  more  developed 
its  nervous  centers,  espe- 
cially its  brain,  and  the 
more  it  is  able  to  capitalize 
its  sensory  impulses ;  also 
the  greater  the  degree  of 
possible  improvement  by 
experience,  a  difference  well 
seen  in  blind  men  whose 
ability  to  succeed  in  life 
without  vision  is  largely  in  proportion  to  their  innate  and 
acquired  mental  powers.  Inasmuch  as  all  cells  require  rest, 
one  would  expect  that  under  constant  stimulation  fatigue  would 
soon  result  and  perceptions  be  imperfect.  Hence  it  happens 
that  all  the  senses  fail  when  exercised,  even  for  but  a  short  pe- 
riod, without  change  of  stimulus  leading  to  alteration  of  con- 
dition in  the  central  cells.  The  change  need  not  be  one  of  en- 
tire rest,  but  merely  a  new  form  of  exercise.  Hence  the  fresh- 
ness experienced  by  a  change  of  view  on  passing  through  beau- 
tiful scenery. 

Exhaustion  may  not  be  confined  wholly  to  the  central  nerve- 
cells,  but  there  can  be  little  doubt  that  they  are  the  most  af- 
fected. Since  also  there  must  be  a  certain  momentum,  so  to 
speak,  to  molecular  activity,  it  is  not  surprising  that  we  find 
that  the  sensation  outlasts  the  stimulus  for  a  brief  period  ;  and 
this  applies  to  all  the  senses,  and  necessarily  determines  the 
rapidity  with  which  the  successive  stimuli  may  follow  each 
other  without  causing  a  blending  of  the  sensations. 

Thus,  then,  in  every  sense  we  must  recognize  (1)  an  end- 
organ  in  which  the  chain  of  processes  begins ;  (2)  a  conducting 
nerve  through  which  (3)  the  central  nerve-cells  are  affected ; 
and  we  may  speak,  therefore,  of  (1)  sensory  impulses  and  (2) 


THE  SKIN  AS  AN  ORGAN  OF  SENSE.  551 

sensations,  when  these  give  rise  to  affections  of  the  central 
nervous  cells  resulting  in  (1)  perceptions  and  (2)  judgments, 
when  we  take  into  account  the  psychic  processes ;  and,  from  the 
nature  of  cell-life  generally,  we  must  recognize  a  certain  inten- 
sity of  the  stimulus  necessary  to  arouse  a  sensation  and  a  limit 
within  which  alone  we  have  power  to  discriminate  (range  of 
stimulation  and  perception) ;  and  also  a  limit  to  the  rapidity 
with  which  stimuli  may  succeed  each  other  to  any  advantage, 
so  as  to  give  rise  to  new  sensations ;  and  a  limit  to  the  endur- 
ance of  the  apparatus  in  good  working  condition  corresponding 
to  clear  mental  perceptions,  together  with  the  value  of  past  ex- 
perience in  the  interpretation  of  our  sensations. 


THE  SKIN  AS  AN  ORGAN  OF  SENSE. 

Bearing  in  mind  that  all  the  sensory  organs  originate  in 
the  ectoderm,  we  find  in  the  skin  even  of  the  highest  animals 
the  power  to  give  the  central  nervous  system  such  sense-im- 
pressions as  bear  a  relation  to  the  original  undifferentiated 
sensations  of  lower  forms  as  derived  from  the  general  surface 
of  the  body,  but  with  less  of  specialization  than  is  met  with  in 
the  sense  of  hearing  and  vision ;  so  that  it  is  possible  to  under- 
stand how  it  is  that  the  skin  must  be  regarded  not  only  as  the 
original  source  of  sensory  impulses  for  the  animal  kingdom, 
but  why  it  still  remains  perhaps  the  most  important  source  of 
information  in  regard  to  the  external  world,  and  the  condition 
of  our  own  bodies ;  for  it  must  be  remembered  that  the  data 
afforded  for  sensory  judgments  by  all  the  other  senses  must 
be  interpreted  in  the  light  of  information  supplied  by  the  skin. 
We  really  perceive  by  the  eye  only  retinal  images.  The  dis- 
tance, position,  shape,  etc.,  of  objects  are  largely  determined  by 
feeling  them,  and  thus  associating  with  a  certain  visual  sensa- 
tion others  derived  from  the  skin  and  the  muscles,  which  latter 
are,  however,  generally  also  associated  with  tactile  sensations. 

It  is  recorded  of  those  blind  from  birth  that,  when  restored 
to  sight  by  surgical  operations,  they  find  themselves  quite 
unalde  to  interpret  their  visual  sensations ;  or,  in  other  words, 
seeing  they  do  not  understand,  but  must  learn  by  the  other 
senses,  especially  tactile  sensibility,  what  is  the  real  nature  of 
tlie  objects  that  form  images  on  their  retinae.  All  objects  seen 
apjx-ar  to  be  against  the  eyes,  and  any  idea  of  distance  is  out 
of  the  question. 


552  ANIMAL   PHYSIOLOGY. 

In  man  special  forms  of  end-organs  are  found  scattered  over 
the  skin,  mucons  and  serous  surfaces  of  the  body,  such  as 
Pacinian  corpuscles,  touch-corpuscles,  end-bulbs,  etc.  •  while  in 
lower  forms  of  vertebrates  many  others  are  found  in  parts 
where  sensibility  is  acute.  There  seems  to  be  little  doubt  that 
these  are  all  concerned  with  the  various  sensory  impulses  that 
originate  in  the  parts  where  they  are  found,  but  it  is  not  pos- 
sible at  present  to  assign  definitely  to  each  form  its  specific 
function. 

It  has  been  contended  that  the  various  specific  sensations 
of  taste,  as  bitter,  sweet,  etc.,  are  the  result  of  impulses  con- 
veyed to  the  central  nervous  system  by  fibers  that  have  this 
function,  and  no  other ;  and  a  like  view  has  been  maintained 
for  those  different  sensations  that  originate  from  the  skin. 
For  such  a  doctrine  there  is  a  certain  amount  of  support  from 
experiment  as  well  as  analogy ;  but  the  more  closely  the  subject 
is  investigated  the  more  it  appears  that  the  complexity  of  our 
sensations  is  scarcely  to  be  explained  in  so  simple  a  way  as 
many  of  these  theories  would  lead  us  to  believe.  Whether 
there  are  nerve-fibers,  with  functions  so  specific,  must  be  re- 
garded as  at  least  not  yet  demonstrated. 

Let  us  now  examine  into  the  facts.  What  are  the  different 
sensations,  the  origin  of  which  must  be  in  the  first  instance 
sought  in  the  skin,  as  the  impulses  aroused  in  some  form  of 
end-organ  or  nerve-termination  ? 

Suppose  that  one  blindfolded  lays  his  left  hand  and  arm 
on  a  table,  and  a  piece  of  iron  be  placed  on  the  palm  of  his 
hand,  he  may  be  said  to  be  conscious  of  the  nature  of  the  sur- 
face, whether  rough  or  smooth,  of  the  form,  of  the  size,  of  the 
weight,  and  of  the  temperature  of  the  body ;  in  other  words, 
the  subject  of  the  experiment  has  sensations  of  pressure,  of 
tactile  sensibility,  and  of  temperature  at  least,  if  not  also  to 
some  extent  of  muscular  sensibility.  But  if  the  right  hand  be 
used  to  feel  the  object  its  form  and  surface  characters  can  be 
much  better  appreciated ;  while,  if  the  body  be  poised  in  the 
hand,  a  judgment  as  to  its  weight  can  be  formed  with  much 
greater  accuracy.  The  reason  of  the  former  is  to  be  sought  in 
the  fact  that  the  finger-tips  are  relatively  very  sensitive  in 
man,  and  that  from  experience  the  mind  has  the  better  learned 
to  interpret  the  sensory  impulses  originating  in  this  quarter ; 
which  again  resolves  itself  into  the  particular  condition  of  the 
central  nerve-cells  associated  with  the  nerve-fibers  that  convey 
inward  the  impulses  from  those  regions  of  the  skin.     Mani- 


THE  SKIN  AS  AN  ORGAN  OP  SENSE.  553 

festly  if  there  be  a  sense  referable  to  the  muscles  (muscular 
sense)  at  all,  when  they  are  contracted  at  will  the  impression 
must  be  clearer  than  when  they  but  feebly  respond  to  the 
mere  pressure  of  some  body. 

It  is  possible,  as  every  one  knows,  to  attend  only  to  the  data 
afforded  by  one  set  of  impulses,  such  as  those  associated  with 
cur  sensations  of  weight,  temperature,  etc.,  but  such  requires 
special  attention ;  and  as  in  the  case  of  the  eye  we  consider  the 
object  as  a  whole,  its  color,  form,  size,  and  other  qualities,  so 
does  the  mind  form  its  complete  conception  by  a  synthesis  or 
union  of  a  variety  of  sensory  data.  Regarding  the  skin  as  a 
whole,  we  may  speak  of  the  skin-sense  as  we  do  of  the  ocular 
sense  or  vision.  The  separate  treatment  of  tactile,  thermal,  and 
other  forms  of  sensibility  under  separate  headings  is  a  matter 
of  convenience ;  but  there  is  considerable  danger  that  we  over- 
look the  great  fundamental  fact  that  our  knowledge  of  objects 
is  primarily  synthetic  and  not  analytic.  True,  in  disease,  when 
one  or  more  sets  of  the  data  of  sense  as  derived  from  the  skin 
is  wanting,  the  others  can  be  appreciated,  and  these  alone. 
Nevertheless,  such  is  an  abnormal  condition,  and  in  that  case 
the  outer  world  passes  to  a  large  extent  beyond  the  degree  of 
control  natural  to  man. 

Pathological. — It  does  happen  in  certain  forms  of  disease, 
notably  of  the  spinal  cord,  that  tactile  sensibility  is  retained 
and  thermal  lost,  or  the  muscular  sense  impaired.  Such  per- 
sons are  plainly  reduced  at  once  to  the  condition,  not  only  of 
being  without  certain  sensory  impressions,  but  in  consequence 
unable  to  use  others  which  they  do  possess  to  the  same  extent 
as  before.  A  man  with  that  affection  of  the  spinal  cord  known 
as  locomotor  ataxy  may  have  tactile  and  thermal  sensibility, 
yet  be  unable  to  use  these,  in  the  absence  of  the  muscular  sense 
to  enable  him  to  be  his  own  master,  except  when  he  calls  in  the 
help  of  his  eyes,  as,  e.  g.,  in  walking. 

It  is  thus  seen  how  all  the  various  sources  of  information 
from  the  skin  and  muscles  blend  psychically  to  produce  a 
conception  which,  as  a  whole,  corresponds  to  "seeing."  The 
defects  just  referred  to  are  in  a  measure  comparable  to  color- 
blindness. 

With  this  warning  we  shall  now  attempt  to  state  some  of 
the  main  facts  in  regard  to  the  different  functions  of  the  skin 
as  a  sensory  organ,  especially  endeavoring  to  trace  parallel  laws 
for  this  and  the  other  senses. 


554  ANIMAL  PHYSIOLOGY. 

Pressure  Sensations. 

1.  There  is  a  relation  between  the  intensity  of  the  stimulus 
and  the  sensation  resulting,  and  this  limit  is  narrow.  The 
greater  the  stimulus  the  more  pronounced  the  sensation,  though 
ordinary  sensibility  soon  passes  into  pain.  Weber's  law  (to  be 
explained  later)  holds  in  the  case  of  the  skin  as  for  other  senses, 
2.  The  duration  of  the  sensation  is  very  brief.  It  is  said  that  a 
card  in  which  holes  have  been  punched,  so  that  when  in  rota- 
tion it  may  bear  on  the  skin,  may  be  made  to  touch  one  of  its 
holes  against  the  finger  as  often  as  fifteen  hundred  times  in  a 
second  before  the  sensations  are  fused.  3.  The  law  of  contrast 
may  be  illustrated  by  passing  the  finger  up  and  down  in  a  ves- 
sel containing  mercury,  when  the  pressure  will  be  felt  most  dis- 
tinctly at  the  point  of  contact  of  the  fluid.  4.  Pressure  is  much 
better  estimated  by  some  parts  than  others ;  hence  the  use  of  the 
tips  of  the  fingers  in  counting  the  pulse,  palpating  tumors,  etc. 

Thermal  Sensations. 

1.  The  law  of  contrast  is  well  illustrated  by  this  sense ;  in 
fact,  the  temperature  of  a  body  exactly  the  same  as  that  of  the 
part  of  the  skin  applied  to  it  can  scarcely  be  estimated  at  all. 
The  first  plunge  into  a  cold  bath  gives  the  impression  that  the 
water  is  much  colder  than  it  seems  in  a  few  seconds  after,  when 
the  temperature  has  in  reality  changed  but  little ;  or,  perhaps, 
the  subject  may  be  better  illustrated  by  dipping  one  hand  into 
warmer  and  the  other  into  colder  water  than  that  to  be  ad- 
judged. The  sample  feels  colder  than  it  really  is  to  the  hand 
that  has  been  in  the  warm  water,  and  warmer  than  it  is  to  the 
other.  2.  The  limit  within  which  we  can  discriminate  is  at  most 
small,  and  the  nicest  determinations  are  made  within  about  27° 
and  33°  C. — i.  e.,  not  far  from  the  normal  temperature  of  the 
body.  3.  Variations  for  the  different  parts  of  the  skin  are 
easily  ascertained,  though  they  do  not  always  correspond  to 
those  most  sensitive  to  changes  in  pressure.  The  cheeks,  lips, 
and  eyelids  are  very  sensitive  to  pressure. 

Recent  investigations  have  revealed  the  fact  that  there 
are  in  the  skin.  "  pressure-spots,"  and  "  cold-spots  "  and  "  heat- 
spots"— i.  e.,  the  skin  may  be  mapped  out  into  very  minute 
areas  which  give  when  touched  a  sensation  of  pressure  differ- 
ent from  that  produced  by  the  same  stimulus  in  the  intermedi- 
ate regions ;  and  in  like  manner  are  there  areas  which  are  sen- 


THE  SKIN  AS  AN   ORGAN  OF  SENSE.  555 

sitive  to  Tvarm  and  to  cold  bodies  respectively,  but  not  to  both ; 
and  these  do  not  correspond  with  the  pressure-spots,  nor  to 
those  that  give  rise  when  touched  to  the  sensation  of  pain. 
These  spots  are  not  placed  symmetrically  on  both  sides  of  the 
same  individual,  nor  on  corresponding  parts  of  different  indi- 
viduals. So  much  has  been  ascertained  by  experiment.  It  is 
believed  by  some  of  the  investigators  that  these  areas  are  con- 
nected with  the  nerve-centers  by  nerve-fibers  devoted  to  con- 
ducting impulses  corresponding  to  the  sensations  which  have 
the  beginning  of  their  formation  in  the  different  kinds  of  spots. 
The  latter,  however,  has  not  been  demonstrated. 

While  there  can  be  no  doubt  that  these  investigations  have 
furnished  additional  facts  of  great  importance,  they  can  not  be 
considered  as  making  the  whole  subject  of  sensation  by  the 
skin  perfectly  clear.  For  example,  how  are  we  to  exj^lain  why 
a  cold  body  feels  heavier  than  a  warm  one,  as  may  easily  be 
demonstrated  to  one's  own  satisfaction  by  placing  a  large  coin 
cooled  down  to  near  the  freezing-point  on  the  forehead  beside 
a  warmer  one  ?  We  think  such  facts  are  calculated  to  enforce 
the  lesson  which  we  have  been  endeavoring  to  impress,  viz., 
that  our  sensations  are  never  single  (thermal,  tactile,  etc.),  but 
are  compound,  one  or  the  other  element  preponderating ;  and 
that  all  interpretations  of  sense  must  take  into  account  this 
fact — and  the  very  important  one — that  every  sensory  impres- 
sion is  interpreted  in  the  light  of  our  past  experience,  as  well 
as  that  of  the  immediate  present. 

It  has  been  shown,  also,  that  the  extent  of  the  area  of  skin 
stimulated  determines  to  a  large  degree  the  quality  of  the  re- 
sulting sensation.  Thus,  the  temperature  of  a  fluid  does  not 
seem  the  same  to  a  finger  and  the  entire  hand.  This  fact  is  not 
irreconcilable  with  the  existence  of  the  various  kinds  of  ther- 
mal spots,  referred  to  above,  but  it  does  re-enforce  the  view  we 
are  urging  of  the  complexity  of  those  sensations  which  seem  to 
us  to  form  simple  wholes— as,  indeed,  they  do  — just  as  a 
piece  of  cloth  may  be  made  up  of  an  unlimited  number  of 
different  kinds  of  threads. 

Tactile  Sensibility. 

As  a  matter  of  fact,  one  may  learn,  by  using  a  pair  of  com- 
passes, that  the  difl'erent  parts  of  the  surface  of  our  bodies  are 
not  equally  sensitive  in  the  discrimination  between  the  contact 
of  bodies— i.  e.,  the  judgment  formed  as  to  whether  at  a  given 


556  ANIMAL  PHYSIOLOGY. 

instant  the  skin  is  being  touched  by  one  or  two  points  is  de- 
pendent on  the  part  of  the  body  with  which  the  points  are 
brought  into  contact. 

The  following  table  will  make  this  clear,  the  numbers  indi- 
cating the  distance  at  which  the  two  points  of  a  pair  of  com- 
passes must  be  apart  in  order  that  they  shall  not  give  rise  to 
the  judgment  of  one  point  of  contact,  but  be  recognized  as  two : 

Millimetres. 

Tip  of  tongue 1  "1 

Palm  of  last  phalanx  of  finger 3*2 

Palm  of  second  phalanx  of  finger 4'4 

Tip  of  nose 6*6 

Whitish  part  of  lips 8"8 

Back  of  second  phalanx  of  finger ll'l 

Skin  over  malar  bone 15"4 

Back  of  hand 29*8 

Forearm 39-6 

Sternum 44"0 

Back 66-0 

There  seem  to  be  areas  of  skin  which  give  rise  when  pricked 
to  the  sensation  of  pain ;  but,  whether  we  should  distinguish  be- 
tween tactile  and  pressure  sensation  by  reference  to  correspond- 
ing spots,  does  not  yet  seem  clear. 

Certain  it  is  that  exercise  of  these  and  all  the  senses  greatly 
improves  them,  though  it  is  likely  that  such  advance  must  be 
referred  rather  to  the  central  nerve-cells  than  to  the  peripheral 
mechanism.  Careful  comparison  of  blind  and  seeing  children 
has  shown  that  the  blind,  in  forming  their  judgments,  appar- 
ently from  sensations  derived  through  the  skin,  in  reality  use 
much  collateral  help,  which  is  very  variable  and  certainly 
widely  different,  according  to  the  past  experience  and  general 
intelligence  of  the  individual. 

We  practically  distinguish  between  a  great  many  sensations 
that  we  can  neither  analyze  nor  describe,  though  the  very 
variety  of  names  suffices  to  show  how  much  our  interpretation 
of  sense  depends  on  past  experience. 

We  are.  always  able  to  define  the  part  of  our  bodies  touched, 
and  with  great  accuracy,  no  doubt,  owing  to  the  simultaneous 
use  in  early  months  and  years  of  our  lives  of  vision  and  the 
senses  resident  in  the  skin. 

There  are,  however,  transient  illusions  of  sense  which  illus- 
trate the  remark  just  made.     If  a  small  marble  be  placed  be- 


THE  SKIN  AS  AN   ORC^AN  OP  SENSE.  557 

tween  the  radial  side  of  one  finger  and  the  uhiar  side  of  the 
other  (Aristotle's  experiment),  the  subject  of  the  experiment 
being  blindfolded,  it  will  be  judged  as  two  marbles  at  first, 
though  the  tactile  impression  is  soon  corrected,  especially  if  the 
eyes  be  opened.  These  surfaces  of  the  fingers  have  not  been 
accustomed  to  touch  at  the  saiue  time  the  one  body,  hence  the 
illusion. 

An  impression  made  on  the  trunk  of  a  nerve  is  referred  to 
the  peripheral  distribution  of  that  nerve  in  the  skin ;  thus,  if 
the  elbow  be  dipped  in  a  freezing  mixture,  the  skin  around  the 
joint  will  experience  the  sensation  of  cold,  but  a  feeling  of  pain 
will  be  referred  to  the  distribution  of  the  ulnar  nerve  in  the 
hand  and  arm.  The  same  principle  is  illustrated  by  the  com- 
mon experience  of  the  efi:'ects  of  a  blow  over  the  ulnar  nerve, 
the  pain  being  referred  to  the  peripheral  distriljution ;  also  by 
the  fact  that  pain  in  the  stump  of  an  amputated  limb  is  thought 
to  arise  in  the  missing  toes,  etc.  It  is  said  that  when  skin 
transplanted  from  the  forehead  to  the  nose,  to  repair  missing 
parts,  is  touched,  the  sensation  is  located  in  the  original  site 
of  the  skin  (forehead).  In  all  such  facts  we  see  how  dependent 
are  all  our  sensory  judgments  on  our  past  experience,  illustrat- 
ing the  very  important  truth,  with  its  wide  ramifications,  that, 
in  a  physiological  sense,  as  well  as  in  many  others,  our  past 
makes  our  own  future  and  that  of  the  race  to  a  very  large 
extent. 

The  Muscular  Sense. 

Every  one  must  be  aware  how  difficult  it  is  to  regulate  his 
movements  when  the  limbs  are  cold  or  otherwise  deadened  in 
sensibility.  We  know  too  that,  in  judging  of  the  muscular 
effort  necessary  to  be  put  forth  to  accomplish  a  feat,  as  throw- 
ing a  ball  or  lifting  a  weight,  we  judge  by  our  past  experi- 
ence. It  is  ludicrous  to  witness  the  failure  of  an  individual 
to  take  up  a  mass  of  metal  which  was  mistaken  for  wood.  In 
these  facts  we  recognize  that  in  the  successful  use  of  the  mus- 
cles we  are  dependent,  not  alone  on  the  sensations  derived  from 
the  skin,  but  also  from  the  muscles  themselves.  True,  the  mus- 
cles are  not  very  sensitive  to  pain  when  cut ;  it  does  not,  how- 
ever, folhiw  that  they  may  not  be  sensitive  to  that  different 
effect,  tlii'ir  own  contraction  ;  whether  the  numerous  Pacinian 
bodies  around  joints,  or  tlie  end-organs  of  the  nerves  of  mus- 
cles are  directly  concerned,  is  not  determined. 

Pathological. — The  teaching  of  disease  is  plainly  indicative  of 


558  ANIMAL  PHYSIOLOGY. 

the  importance  of  sensations  derived  both  from  the  skin  and 
the  muscles  for  co-ordination  of  muscular  movements. 

In  locomotor  ataxy,  in  which  the  power  of  muscular  co- 
ordination is  lost  to  a  large  extent,  the  lesions  are  in  the  pos- 
terior columns  of  the  spinal  cord,  or  the  posterior  roots  of  the 
nerves,  or  both,  and  these  are  the  parts  involved  in  the  trans- 
mission of  afferent  impulses. 

Whether  the  muscular  sense  also  implies  a  central "  neural " 
sense,  or  consciousness  of  the  changes  of  central  origin,  associ- 
ated with  the  execution  of  a  movement  as  distinct  from  the 
impressions  derived  from  the  muscles,  is  a  matter  of  dispute. 
But  the  student  will  he  already  prepared  for  our  answer  to  this 
question.  The  evidence  of  experiment  seems  to  point  to  a  dis- 
tinct source  of  information  in  the  muscles.  We  would  take 
along  with  this  the  additional  data  of  sense  afforded  by  the  skin, 
the  "  sense  of  effort "  and  other  factors,  as  stored  past  experi- 
ence, which  must  be  very  variable  for  the  individual,  as  any 
one  may  observe  by  watching  the  muscular  efforts  of  others 
and  himself. 

Comparative. — The  more  closely  the  higher  vertebrates  are 
observed,  the  more  convinced  does  one  become  that  those  sen- 
sory judgments,  based  upon  the  information  derived  from  the 
skin  and  muscles,  which  they  are  constantly  called  upon  to  form 
are  in  extent,  variety,  and  perfection  scarcely  if  at  all  surpassed 
by  those  of  man.  Of  course,  a  sensory  judgment  in  man,  with 
his  excessive  cerebral  development,  may  by  associations  in  his 
experience  be  worked  up  into  elaborate  judgments  impossible 
to  the  brutes,  but  we  now  refer  to  the  judgments  of  sense  in 
themselves. 

The  lips,  the  ears,  the  vibrissse  or  stiff  hairs,  especially 
about  the  lips,  the  nose,  in  some  cases  the  paws,  all  afford  deli- 
cate and  extensive  sensory  data. 

It  is  a  remarkable  fact  that  the  most  intelligent  of  the 
groups  of  animals  have  these  sensory  surfaces  well  developed, 
as  witness  the  elephant  with  his  wonderful  trunk,  the  hand 
of  the  monkey,  and  the  paws  and  vibrissae  of  the  cat  and  dog 
tribe. 

On  the  other  hand,  the  groups  with  hoofs  are  notably  inferior 
in  the  mental  scale.  When  we  pass  to  the  lower  forms  of  in- 
vertebrates the  appreciation  of  vibrations  of  the  air  or  water 
in  which  they  live,  of  its  temperature,  of  its  pressure,  must  be 
considerable  to  enable  them  to  adapt  themselves  to  a  suitable 
environment. 


VISION.  559 

We  have  not  spoken  of  sensations  derived  from  the  internal 
organs  and  surfaces.  These  are  ill-defined,  and  we  know  them 
mostly  either  as  a  vague  sense  of  comfort  or  discomfort,  or  as 
actual  pain.  We  are  quite  unable  to  refer  them  at  present  to 
special  forms  of  end-organs.  They  are  valuable  as  reports  and 
warnings  of  the  animal's  own  condition. 

After-impressions  ("  after-images  ")  of  all  the  senses  referred 
to  exist,  mostly  positive  in  nature — i.  e.,  the  sensation  remains 
when  the  stimulus  is  withdrawn. 

Synoptical. — The  information  derived  from  the  skin  in  man 
and  the  other  higher  vertebrates  relates  to  sensations  of  press- 
ure, temperature,  touch,  and  pain.  The  muscles  also  supply 
information  of  their  condition.  In  how  far  these  are  referable 
to  certain  end-organs  in  the  skin  is  uncertain.  There  are  der- 
mal areas  that  give  rise  to  the  sensations  of  heat,  cold,  pressure, 
and  pain.  Whether  these  are  connected  with  nerve-fibers  that 
convey  no  other  forms  of  impulses  than  those  thus  arising  is 
undetermined. 

In  all  these  senses  the  laws  of  contrast,  duration  of  the  im- 
pression, limit  of  discrimination,  etc.,  hold. 

The  sensory  judgments  based  on  sensations  derived  from 
the  skin  are  syntheses  or  the  result  of  the  blending  of  many 
component  sensations  simultaneous  in  origin.  All  our  sensory 
judgments  are  very  largely  dependent  on  our  past  experience. 


VISION. 

Light  and  vision  are  to  some  degree  correlatives  of  each 
other.  Light  is  supposed  to  have  as  its  physical  basis  the  vibra- 
tions of  an  imponderable  ether.  Such  is,  however,  to  a  non- 
seeing  animal  as  good  as  non-existent,  so  that  we  may  look  at 
this  subject  either  with  the  eyes  of  the  physiologist  or  the  phys- 
icist, according  as  we  regard  the  cause  of  the  effects  or  the 
latter  and  their  relations  to  one  another.  It  is,  however,  im- 
po.ssible  to  understand  the  physiology  of  vision  witliout  a 
.sound  knowledge  of  the  anatomy  of  the  eye,  and  an  apprehen- 
sion of  at  least  some  of  tlu;  laws  of  the  science  of  optics.  The 
student  is,  therefore,  recommended  to  learn  practically  the 
coarse  and  microscopic  structure  of  the  eye  in  detail.  The  eyes 
of  mammals  are  sufficiently  alike  to  make  the  dissection  of  any 
of  them  profitable.  Bullocks'  eyes  are  readily  obtainable,  and 
from  their  large  size  may  be  used  to  advantage.     We  recom- 


560 


ANIMAL  PHYSIOLOGY. 


Fig.  403.— Eye  partially  dissected  (after  Sappey).  1,  optic  nerve  ;  2,  3.  4,  sclerotic  dissected 
back  so  as  to  uncover  the  choroid  coat ;  5,  cornea,  divided  and  folded  back  with  sclerotic 
coat ;  6,  canal  of  Schlemm  ;  7,  external  surface  of  choi-oid,  traversed  by  one  of  the  long 
ciliary  arteries  and  by  ciliary  nerves  ;  8,  central  vessel,  into  which  the  vasa  vorticosa 
empty :  9,  10,  choroid  zone  ;  11,  ciliary  nerves  ;  12,  long  ciliary  artery  ;  13,  anterior  ciliary 
arteries  ;  14,  iris  ;  15,  vascular  circle  of  iris  ;  16,  pupil. 

mend  one  to  be  boiled  hard,  another  to  be  frozen,  and  sections 
in  different  meridians  to  be  made,  especially  one  vertical  longi- 


SUPERIOR  RECTUS 


CHOROID 


OPTIC  NERVE 


CHOROID 


NFERIOH  RECTUS 


Fig.  403.— Section  of  human  eye,  somewhat  diagrammatic  (after  Flint). 


VISION. 


561 


tudinal  section.     Other  specimens  may  be  dissected  with  and 
without  the  use  of  water. 


Fio.  404.— Certain  parts  of  eye.  1  x  10.  (After  Sappey.)  1, 1,  crystalline  lens ;  2.  hyaloid 
membrane  :  3,  zonule  of  Zinn  :  4,  iris ;  5,  a  ciliary  process  :  6,  radiating-  fibers  of  ciliary 
miLscle  :  7,  section  of  circular  portion  of  ciliary  muscle  ;  8,  venous  plexus  of  ciliary  mus- 
cle ;  9.10.  sclerotic  coat;  11,  1:J,  cornea;  13,  epithelial  layer  of  cornea;  14.  Descemet's 
membrane  ;  15,  pectinate  ligament  of  iris  ;  16,  epithelium  of  membrane  of  Descemet ;  17. 
union  of  sclerotic  coat  with  cornea  ;  18,  section  of  canal  of  Schlemm. 


Assuming  that  some  such  work  has  been  done,  and  that  the 
student  has  become  quite  familiar  with  the  general  structure 
of  the  eye,  we  call  attention  specially  to  the  strength  of  the 
sclerotic  coat ;  the  great  vascularity  of  the  choroid  coat  and  its 
terminal  ciliary  processes,  its  pigmented  character  adapting  it 
for  the  absorption  of  light ;  the  complicated  structure  and  pro- 
tected position  of  the  retinal  expansion.  It  may  be  said  that 
the  whole  eye  exists  for  the  retina,  and  that  the  entire  meclian- 
ism  besides  ia  subordinated  to  the  formation  of  images  on  this 
nei-vouH  exi)ansion.  The  eye  of  the  mammal  may  be  regarded 
as  an  arrangement  of  refracting  media,  protected  by  coverings, 
with  a  window  for  the  admission  of  light,  a  curtain  regulating 
th(^  quantity  admittfjd;  a  sensitive  screen  on  which  the  images 
are  thrown;  surfaces  for  the  ab.sorption  of  superfluous  light; 
86 


562 


ANIMAL  PHYSIOLOGY. 


apparatus  for  the  protection  of  the  eye  as  a  whole,  and  for 
preserving  exposed  parts  moist  and  clean. 

Embryological. — We  have  already  learned  that  the  first  indi- 
cation of  the  eye  is  the  formation  of  the  optic  vesicle,  an  out- 
growth from  the  first  cerebral  vesicle.  This  optic  vesicle  be- 
comes more  contracted  at  the  base,  and  the  optic  stalk  remains 
as  the  optic  nerve. 


Fig.  406. 


Fig.  405. 

Fig.  405.— Section  through  head  of  chick  on  third  day,  sho-wing  origin  of  eye  (after  Yeo").  a, 
epiblast  undergoing  thickening  to  form  lens  ;  o,  optic  vesicle  ;  Vj,  first  cerebral  vesicle  : 
Vq,  posterior  cerebral  vesicle.  It  will  be  observed  that  the  retina  is  already  distinctly  in- 
dicated. 

Fig.  406.— Later  stages  in  development  of  eye  (after  Cardiat).  a,  epiblast ;  c,  developing 
lens ;  o,  optic  vesicle. 

At  an  early  stage  of  development  (second  or  third  day  in  the 
chick)  the  outer  portion  of  the  optic  vesicle  is  pushed  inward, 
so  that  the  cavity  is  almost  obliterated ;  the  anterior  portion, 
becoming  thickened,  ultimately  forms  the  retina  proper,  while 
the  posterior  is  represented  by  the  tesselated  pigment  layer  of 
the  choroid. 

As  this  retinal  portion  breaks  away  from  the  superficial  epi- 
thelium, the  latter  forms  an  elliptical  mass  of  cells,  the  future 
lens,  the  changes  of  which  in  the  formation  of  the  cells  peculiar 
to  the  lens  illustrate  to  how  great  lengths  differentiation  in 
structure  is  carried  in  the  development  of  a  single  organ.  It 
will  thus  be  seen  that  the  most  essential  parts  of  the  eye,  the 
optic  nerve,  the  retina,  and  the  crystalline  lens,  are,  according 
to  a  general  law,  the  earliest  marked  out.  The  cornea,  the  iris, 
the  choroid,  the  vascular  supply,  the  sclerotic,  etc.,  are  all  sec- 
ondary in  importance  and  in  formation  to  these,  and  are  derived 
from  the  mesoblast,  while  the  essential  structures  are  traceable, 
like  the  nervous  system  itself,  to  the  epiblastic  layer. 


VISION. 


563 


Any  act  of  perfect  vision  in  a  mammal  may  be  shown  to 
consist  of  the  following :  (1)  The  focusing  of  rays  of  light  from 


h— 


Fio.  407.— More  advanced  stage  of  development  of  eye  (after  Cardiat).  a,  epithelial  cells 
forming  lens,  now  much  altered  :  h,  lens  capsule  ;  c,  cutaneous  tissue  about  to  form  con- 
junctiva ;  rf.  e,  two  layers  of  optic  vesicle,  now  folded  back  and  forming  retina ;  /.  mucous 
tissue  forming  vitreous  humors ;  g,  intercellular  substance  ;  /i,  developing  optic  nerve  ; 
i,  nerve-fibers  entering  retina. 

an  object  on  the  retina,  so  as  to  form  a  well-defined  image ;  (2) 
the  conduction  of  the  sensory  impulses  thus  generated  in  the 
retina  by  the  optic  nerve  inward  to  certain  centers ;  and  (3)  the 
elaboration  of  these  data  in  consciousness. 

We  thus  have  the  formation  of  an  image — a  physical  pro- 
cess; sensation,  perception,  and  judgment — physiological  and 
psychical  processes. 

In  the  natural  order  of  things  we  must  discuss  first  those 
arrangements  which  are  concerned  with  the  focusing  of  light 
— i.  e.,  the  formation  of  the  image  on  the  retinal  screen. 


Dioptrics  op  Vision, 

One  of  the  most  satisfactory  methods  of  ascertaining  that 
the  eye  does  form  images  of  the  objects  in  the  field  of  vision 
is  to  remove  the  eye  of  a  recently  killed  albino  rabbit.     On 


564 


ANIMAL  PHYSIOLOGY. 


holding  up  "before  such  an  eye  any  small  object,  as  a  pair  of 
forceps,  it  may  be  readily  observed  that  an  inverted  image  of 
the  object  is  formed  on  the  back  of  the  eye  (fundus).  If,  how- 
ever, the  lens  be  removed  from  such  an  eye,  no  image  is  formed. 
If  the  lens  be  itself  held  behind  the  object,  an  inverted  image 
will  be  thrown  upon  a  piece  of  paper  held  at  a  suitable  (its 
focal)  distance.  By  substituting  an  ordinary  biconvex  lens,  the 
same  effect  follows.  It  thus  appears,  then,  that  the  lens  is  the 
essential  part  of  the  refracting  media,  though  the  aqueous  and 
vitreous  humors  and  the  cornea  are  also  focusing  mechanisms. 

The  surfaces  of  the  refracting  media  may  all  be  considered 
to  be  centered  on  one  of  the  axes,  which  meets  the  retina  above 
and  to  the  inner  side  of  the  fovea  centralis.  We  may  for 
practical  purposes  reason  from  a  diagrammatic  eye,  the  re- 
fracting surfaces  of  which  are  (1)  the  anterior  surface  of  the 
cornea,  (2)  the  anterior  surface  of  the  lens,  and  (3)  the  posterior 
surface  of  the  lens.  The  media  may  be  reduced  to  (1)  the  lens 
substance  and  (2)  the  aqueous,  or,  as  it  has  about  the  same 
refracting  power,  the  vitreous  humor. 

By  the  posterior  principal  focus  is  meant  the  point  at  which 
all  rays  that  fall  on  the  cornea  parallel  to  the  optic  axis  are 
focused.  It  is  14*647  mm.  behind  the  posterior  surface  of  the 
lens,  or  22*647  mm.  behind  the  anterior  surface  of  the  cornea  in 


II 

Fig.  408.— Refraction  by  convex  lenses  (after  Flint  and  Weinhold).  The  lens  may  be  assumed 
to  consist  of  a  series  of  lenses  (.H  in  flgxu-e),  for  the  sake  of  simplicity,  though  of  course 
this  is  not  strictly  accurate. 

the  diagrammatic  eye.  In  the  actual  eye  the  fovea  of  the  retina 
must  occupy  this  position  when  at  rest,  if  a  distinct  image  is 
to  be  formed. 

It  will  appear  that  we  may  represent  the  eye  as  reduced  to 


VISION.  565 

tlie  lens  and  the  retina,  and  in  many  of  the  illustrations  to  fol- 
low this  will  be  done.  The  experiments  referred  to  above  will 
con^^nce  the  student  that  such  is  the  case ;  and  we  may  here 
state  that,  while  the  various  principles  involved  in  the  physiol- 
ogy of  vision  may  be  illustrated  in  great  x)erfection  by  elab- 
orate experiments,  we  shall  endeavor  to  supply  the  student 
with  accounts  of  very  simple  methods  of  convincing  himself 
by  personal  observation,  such  as  may  be  readily  repeated  at  a 
future  time,  which  is  more  than  can  be  said  for  those  that  in- 
volve expensive  apparatus. 

Accommodation  of  the  Eye. 

Using  the  material  already  referred  to,  the  student  may 
observe  that,  with  the  natural  eye  of  the  albino  rabbit,  its  lens 
(or  better  that  of  a  bullock's  eye,  being  larger),  or  a  biconvex 
lens  of  glass,  there  is  only  one  position  of  the  instruments  and 
objects  which  will  produce  a  perfectly  distinct  image.  If  either 
the  eye  (retina),  the  lens,  or  the  object  be  shifted,  instead  of  a 
distinct  image,  a  blurred  one,  or  simply  diffusion-circles,  ajDpear. 

A  j)hotographer  must  alter  either  the  position  of  the  object 
or  the  position  of  his  lens  when  the  focus  is  not  perfect.  The 
eye  may  be  compared  to  a  camera,  and  since  the  retina  and 
lens  can  not  change  position,  either  the  shape  of  the  lens  must 
change  or  the  object  assume  a  different  position  in  space.  As 
a  matter  of  fact,  any  one  may  observe  that  he  can  not  see 
objects  distinctly  within  a  certain  limit  of  nearness  to  the  eye, 
known  as  the  near  point  {punctum  proximum) ;  while  he  be- 
comes conscious  of  no  effect  referable  to  the  eye  until  objects 
approach  within  about  sixty-five  to  seventy  yards.  Beyond 
the  latter  distance  objects  are  seen  clearly  without  any  effort. 
We  thus  learn  that  the  range  of  accommodation  lies  between 
about  five  inches  and  sixty  to  seventy  yards,  though  it  is  cus- 
tomary to  speak  of  the  far  point  as  infinity  (cc),  which  simply 
means  that  the  rays  from  objects  beyond  the  distance  given 
aViove  are  practically  parallel,  and  are,  therefore,  focused  on 
the  retina  without  any  alteration  in  the  shajje  of  the  lens  {neg- 
ative accommodation) ;  while  nearer  ones  require  this.  When 
objects  are  nearer  to  the  eye  than  about  five  inches,  for  most 
f>ersons,  the  eye  can  not  accommodate  sufficiently  to  ))ring  the 
rays  f>f  light  emanating  from  them  to  a  focus  on  the  retina. 

There  are  many  ways  in  which  we  may  be  led  to  realize 
these  truths  :   1.  When  one  is  reading  a  printed  page  it  is  only 


566 


ANIMAL  PHYSIOLOGY. 


the  very  few  words  to  which  the  eyes  are  then  specially  di- 
rected that  are  seen  clearly,  the  rest  of  the  page  appearing 
blurred ;  and  the  same  holds  for  the  objects  in  any  small  room. 
We  speak  of  picking  out  an  acquaintance  in  an  audience  or 
crowd,  which  implies  that  each  of  the  individuals  composing 
the  throng  is  not  distinctly  seen  at  the  same  time.  2.  If  an  ob- 
server hold  up  a  finger  before  his  eyes,  and  direct  his  gaze  into 
the  distance  (relax  his  accommodation),  presently  he  will  be- 
hold a  second  shadowy  finger  beside  the  real  one — i.  e.,  he  sees 
double :  his  eyes,  being  accommodated  for  the  distant  objects, 
can  not  adapt  themselves  at  the  same  time  for  near  ones.  3.  The 
principle  involved  may  be  most  precisely  illustrated  by  Schein- 


FiG.  409.— Diagram  to  illustrate  Scheiner's  experiment  (after  Landois). 
cate  the  circumstances  under  which  there  is  double  vision. 


The  dotted  lines  indi- 


FiG.  410.— To  explain  Scheiner's  experiment  (after  Bernstein).  The  object  is  at  o  ;  the  lens  is 
represented  by  b  :  and  the  retina  may  be  at  m,  tn,  n,  n,  or  I,  I.  The  card  with  its  holes, 
e,  /,  is  directly  in  front  of  the  lens.  It  is  plain  that,  if  the  rays  strike  the  retina  in  any  way 
except  as  represented  at  c,  double  images  must  be  formed.  One  or  other  of  these  will 
disappear  according  as  the  right  or  left  hole  of  the  card  is  stopped  ;  which  of  them  will 
depend  on  circumstances— i.  e.,  as  to  whether  the  case  is  that  figured  at  m,  m  or  I,  I. 


VISION.  567 

er's  experiments  (Figs.  409  and  410).  Let  two  small  holes  be 
pricked  in  a  card,  at  a  distance  from  each  other  not  greater 
than  the  diameter  of  the  pupil ;  fix  the  card  upright  on  a  piece 
of  board,  about  two  feet  long,  and,  closing  one  eye,  observe  the 
effect  of  looking  at  two  pins  stuck  into  the  board  in  line  with 
each  other,  at  different  distances  apart.  It  may  be  observed  that 
as  soon  as  the  nearest  pin  is  approximated  to  the  card  within 
a  certain  distance  it  fails  to  be  distinctly  seen,  and  appears 
double — i.  e.,  the  near  point  is  exceeded  ;  that  when  the  distant 
l^in  is  in  focus,  the  near  one  appears  double,  and  vice  versa. 
When  the  image  is  double,  blocking  one  of  the  two  holes 
causes  one  image  to  disappear,  and  this  is  the  right  or  the  left 
hand  image,  according  as  the  one  or  the  other  hole  is  stopped, 
and  as  it  is  the  distant  or  near  pin  that  is  seen  as  two.  The 
reason  of  this  will  be  plain  from  the  above  figures,  but  it  must 
be  remembered  that  an  image  on  the  right  of  the  retina  is  ad- 
judged to  be  on  the  left  of  the  visual  field,  as  will  be  explained 
later. 

In  what  does  accommodation  consist  ?  If  light  from  a  can- 
dle or  lamp  be  allowed  to  fall  obliquely  on  the  eye  of  a  second 
person,  through  a  card  on  which  two  triangular  holes  have 
been  cut  one  above  the  other,  three  pairs  of  images  of  the  flame 
(necessarily  triangular)  may  be  seen  reflected  from  the  eye  of 
the  observed  subject,  two  of  which  are  erect  and  one  inverted ; 
the  brightest  and  most  distinct  being  from  the  cornea,  the  sec- 
ond pair  dimmer  and  larger  from  the  anterior  surface  of  the 
lens,  and  the  smallest  (c)  from  the  posterior  surface  of  the  lens, 
inverted,  since  it  is  produced  by  a  concave  mirror.  When  the 
subject  of  the  observation 
looks  at  a  near  object,  only 
one  of  these  pairs  of  images 
alters  appreciably,  viz.,  that 
fr<jm  the  anterior  surface  of 
the  lens,  the  middle  x>aii*  (b). 

Tlie  conclusion  then  follows  p,^  411.-Purkinje'8  images,  a  h  c  during 
tliat    accommodation    consists  negative   n,  ^c.  during  positive  atcommo- 

dation  (after  Landois). 

'ssentially  in  an  alteration  of 

the  convexity  of  the  anterior  surface  of  the  lens.  The  images 
appear  nearer  to  each  other  the  more  convex  the  lens  becomes. 
Without  the  help  of  a  special  instrument  (phakoscope)  the  ob- 
s(^TV<;T  may  fail  to  see  th(;  change,  though  that  the  other  pairs 
do  not  alter  position  or  size;  he  may  certainly  readily  observe. 
This  change  in  tlie  shape  of  the  lens  is  accomplished  as 


568  ANIMAL  PHYSIOLOGY. 

follows :  The  lens  is  naturally  very  elastic  and  is  kept  in  a  par- 
tially compressed  condition  by  its  capsule,  to  which  is  attached 
the  suspensory  ligament  which  has  a  posterior  attachment  to 
the  choroid  and  ciliary  processes.     When  the  ciliary  muscle. 


Fig.  412.— Illustrates  mechanism  of  accommodation  (after  Flck).  The  left  side  depicts  the 
relation  of  parts  during  the  passive  condition  of  the  eye  (negative  accommodation,  or 
accommodation  for  long  distances) ;  the  right  side,  that  for  near  objects. 

which  operates  from  a  fixed  point  the  corneo-sclerotic  junction, 
pulls  upon  the  choroid,  etc.,  it  relaxes  the  suspensory  ligament ; 
hence  the  lens,  not  being  pressed  upon  in  front  as  it  is  from 
behind  by  the  vitreous  humor  (invested  by  its  hyaloid  mem- 
brane), is  free  to  bulge  and  so  increase  its  refractive  power. 
The  nearer  an  object  approaches  the  eye,  the  greater  the  diver- 
gence of  the  rays  of  light  proceeding  from  it,  and  hence  the 
necessity  for  greater  focusing  power  in  the  lens. 

If  a  person  be  observed  closely  when  looking  from  a  remote 
to  a  near  object,  it  may  be  noticed  that  the  eyes  turn  inward — 
i.  e,,  the  visual  axes  converge  and  the  pupils  contract.  These 
are  not,  however,  essential  in  the  sense  in  which  the  changes 
in  the  lens  are ;  for,  as  before  stated,  in  the  absence  of  the  lens 
distinct  vision  is  quite  impossible.  Were  additional  evidence 
necessary  to  show  that  accommodation  is  effected  as  described, 
it  might  be  stated  that  by  stimulation  of  the  lenticular  gan- 
glion the  ciliary  muscle  may  in  an  animal  thus  experimented 
upon  be  shown  to  contract,  the  choroid  to  be  drawn  forward, 
and  the  anterior  convexity  of  the  lens  to  be  increased.  Vaso- 
motor changes  or  alterations  in  the  size  of  the  iris,  if  they  have 
any  effect  upon  the  lens  at  all,  must  play  a  verj'-  unimportant 
part.  The  movements  of  the  iris  do,  however,  serve  an  impor- 
tant purpose,  and  to  that  subject  we  now  turn. 


VISION. 


569 


Alterations  in  the  Size  of  the  Pupil. 

The  pupil  varies  iu  size  according  as  the  iris  is  iu  a  greater 
or  less  degree  active.  All  observers  are  agreed  that  the  circu- 
lar fibers  around  the  pupillary  margin  are  muscular,  forming 
the  so-called  sphincter  of  the  iris  ;  but  great  differences  of  opin- 
ion still  exist  in  regard  to  the  radiating  fibers.  It  is  thought 
by  many  that  all  the  changes  in  the  iris  may  be  explained  by 
the  elasticity  of  its  structure  without  assuming  the  existence 
of  muscular  fibers  other  than  those  of  the  sphincter ;  thus  a 
contraction  of  the  latter  would  result  in  diminution  of  the  pu- 
pillary aperture,  its  relaxation  to  an  enlargement,  j)rovided  the 
rest  of  the  iris  were  highly  elastic. 

The  conclusions  in  regard  to  the  innervation  of  the  iris  rest 
largely  upon  the  results  of  certain  experiments  which  we  shall 


Brain  above  medulla 


Optic  centre— 


OcuU)-motor\ V  _j^ 

centre 


DUator  centre 


Sptnai  dUator  centre 


Eetina 


Iris 


Sympathetic  nerve  to 
radiating  fibres 


Fio.  413.— Diairram  U>  illnstrnt*-  innfrvation  of  the  iris.    Df)t,t(>(l  linfs  indicatf;  penpral  fiinc- 
Uoiiul  ctiunectiou  (correlation^    Course  of  iiiipulaes  iuiiicaled  by  arrows. 


570  ANIMAL   PHYSIOLOGY. 

now  briefly  detail :  1.  When  the  third  nerve  is  divided,  stimu- 
lation of  the  optic  nerve  (or  retina)  does  not  cause  contraction 
of  the  pupil  as  usual.  2.  When  the  optic  nerve  is  divided,  light 
no  longer  causes  a  contraction  of  the  pupil,  though  stimulation 
of  the  third  nerve  or  its  center  in  the  anterior  portion  of  the 
floor  of  the  aqueduct  of  Sylvius  does  bring  about  this  result. 
.'3.  Section  of  the  cervical  sympathetic  is  followed  by  contrac- 
tion and  stimulation  of  its  peripheral  end  by  dilation  of  the 
pupil. 

From  such  experiments  it  has  been  concluded  that — 1.  The 
optic  is  the  afferent  nerve  and  the  third  nerve  the  efferent  nerve 
concerned  in  the  contraction  of  the  pupil ;  and  that  the  center 
in  the  brain  is  situated  as  indicated  above,  so  that  the  act  is  or- 
dinarily a  reflex.  2.  That  the  cervical  sympathetic  is  the  path 
of  the  efl^erent  impulses  regulating  the  action  of  the  radiating 
fibers  of  the  iris. 

Its  center  has  been  located  near  that  for  the  contraction  of 
the  pupil,  and  it  may  be  assumed  to  exert  a  tonic  action  over 
the  iris  comparable  to  that  of  the  vaso-motor  center  over  the 
blood-vessels. 

The  impulses  may  be  traced  through  the  cervical  sympa- 
thetic and  its  ganglia  back  to  the  first  thoracic  ganglion,  and 
thence  to  the  spinal  cord  and  brain.  There  may  be  subsidiary 
centers  in  the  cervical  spinal  cord. 

There  are  facts  which  it  is  diflicult  to  explain  in  the  above 
manner.  Thus,  when  atropin  is  dropped  into  the  eye,  the  dila- 
tation is  greater  than  that  which  follows  section  of  the  optic 
nerve  or  the  third  nerve.  In  such  a  case,  paralysis  of  the  con- 
tracting mechanism,  by  which  the  dilating  mechanism  is  left 
free  to  act,  should  produce,  we  might  suppose,  the  greatest  pos- 
sible dilation  of  the  pupil,  especially  if  we  assume,  as  some  do, 
that  there  are  no  radiating  muscular  fibers,  but  that  all  the 
effects  are  produced  through  the  sphincter  of  the  iris ;  but  such 
is  not  the  case.  The  result  has  been  set  down  to  the  action  of 
the  drug  upon  a  local  nervous  mechanism,  or  the  muscular 
fibers  themselves,  or  to  the  vaso-motor  changes  said  to  be  co- 
incident. This  view  is  strengthened  by  the  fact  that  stimu- 
lation of  the  retina  in  a  recently  removed  eye  will  cause  some 
reflex  contraction  of  the  pupil.  In  explaining  the  action  of 
drugs  on  the  pupil  we  are  not  limited  to  either  a  purely  local 
or  a  purely  central  influence ;  some  seem  to  act  in  one  stage 
more  upon  the  centers,  in  another  more  locally.  Vaso-motor 
influences  undoubtedly  do  affect  the  size  of  the  pupil,  full  vessels 


VISION.  571 

tending  to  contraction  and  the  reverse  to  dilation.  Upon  the 
whole,  it  seems  best  to  regard  the  two  mechanisms  as  supple- 
mentary to  one  another,  so  that  usually  with  increased  action 
of  the  one  there  is  "diminished  action  of  the  other.  We  find 
that  the  two  eyes  move  in  harmony,  and  that  the  two  pupils  in 
health  are  always  of  the  same  size.  Light  thrown  upon  one 
eye  contracts  the  pupil  of  the  other.  We  are  thus  led  to  be- 
lieve in  associated  or  consensual  movement  of  the  iris,  owing 
to  nervous  connections  between  the  various  centers  involved. 
These  are  physiological,  but  whether  anatomical  or  not,  in  the 
sense  that  annectant  fibers  exist,  is  uncertain ;  and,  however, 
in  the  evolution  of  function,  they  may  have  been  at  first  pro- 
duced, have  been  so  strengthened,  according  to  the  law  of  habit, 
that  now  it  is  with  the  greatest  difficulty  that  one  may  learn 
to  move  one  eye  independently  of  the  other,  or  modify  the 
form  of  the  pupils  without  also  shifting  the  visual  axes. 

It  is  to  be  remembered  that,  although  the  dilating  center  is 
automatic  in  action,  it  may  also  act  reflexly,  or  be  modified  by 
unusual  afferent  impulses — as,  e.  g.,  the  strong  stimulation  of 
any  sensory  nerve  which  causes  enlargement  of  the  pupil 
through  inhibition  of  the  center.  To  render  the  paths  of 
impulses  affecting  the  iris  somewhat  clearer,  it  is  well  to  bear 
in  mind  the  nervous  supply  of  the  part :  1.  The  third  nerve, 
through  the  ciliary  (ophthalmic,  lenticular)  ganglion,  supplies 
•short  ciliary  nerves  to  the  iris,  ciliary  muscle,  and  choroid.  2. 
The  cervical  sympathetic  reaches  the  iris  chiefly  through  the 
long  ciliary  nerves  and  the  ophthalmic  division  of  the  fifth. 
■i.  There  are  sensory  fibers  from  the  fifth  nerve ;  and,  according 
to  some  observers,  also  dilating  fibers  from  this  nerve  inde- 
pendent of  the  sympathetic,  as  well  as  those  that  may  reach 
the  eye  by  the  long  ciliary  nerves  without  entering  the  ciliary 
ganglion.  4.  The  centers  from  which  both  the  contracting  and 
dilating  imj>ulses  proceed  are  situated  near  to  each  other  in 
the  floor  of  the  aqueduct  of  Sylvius.  It  is  of  practical  im- 
portance to  remember  the  various  circumstances  under  which 
the  pupil  contracts  and  dilates. 

Contraction  (Myosis). —  1.  Access  of  strong  light  to  the 
retina.  2.  Associated  contraction  on  accommodation  for  near 
objects.  3.  Similar  associated  contraction  when  the  visual  axes 
converge,  as  in  accommodation  for  near  objects.  4.  Reflex 
stimulation  of  afferent  nerves,  as  the  nasal  or  ophthalmic  divis- 
ion of  the  fifth  nerve.  5.  During  sleep.  0.  Upon  stimulation 
of  the  optic  or  the  third  nerve,  and  the  corpora  quadrigemina 


5Y2 


ANIMAL  PHYSIOLOaY. 


or  adjacent  parts  of  the  brain.  7.  Under  the  effects  of  certain 
drugs,  as  physostigmin,  morphia,  etc. 

Dilation  {Mydriasis). — 1.  In  darkness.  2.  On  stimnlation 
of  the  cervical  sympathetic.     3.  During  asphyxia  or  dyspnoea. 

4.  By  painful  sensations  from  irritation  of  peripheral  parts. 

5.  From  the  action  of  certain  drugs,  as  atropin,  etc.  The 
student  may  impress  most  of  these  facts  upon  his  mind  by 
making  the  necessary  observations,  which  can  be  readily  done. 

Pathological. — As  showing  the  importance  of  such  connec- 
tions, we  may  instance  the  fact  that,  in  certain  forms  of  nervous 
disease  (e.  g.,  locomotor  ataxia),  the  pupil  contracts  when  the 
eye  is  accommodated  to  near  objects,  but  not  to  light  (the 
Argyll-Robertson  pupil).  In  other  cases,  owing  to  brain-dis- 
ease, the  pupils  may  be  constantly  dilated  or  the  reverse ;  or 
one  may  be  dilated  and  the  other  contracted. 

Optical  Imperfections  of  the  Eye. 

The  defects  to  be  noticed  now  are  common  to  all  human 
eyes,  and  probably  to  the  eyes  of  all  mammals,  though  in 
some  persons  certain  of  them,  as  astigmatism,  are  of  so  serious 
a  character  that  they  require  special  remedies. 

Spherical  Aberration. — The  nature  of  this  defect  may  be  best 
learned  from  an  examination  of  Fig.  414,  below.  It  will  be 
seen  that  rays  of  light  passing  through  the  lens  are  brought  to 


Fig.  414.— Illustrating  spherical  aberration  (after  Le  ConteV    The  best  image  is  formed  at  S,  S, 
but  is  not  perfectly  sharply  defined  even  here. 


a  focus,  varying  with  the  point  of  the  lens  through  which  they 
pass,  the  focusing  power  of  any  ordinary  convex  lens  being 
greater  toward  the  circumference.  This  defect  is  believed  to 
be  corrected  in  the  human  eye,  at  least  to  some  extent,  by  the 
following : 

1.  The  iris  cuts  off  the  more  strongly  refracted  outer  rays. 

2.  The  corneal  curvature  is  rather  ellipsoidal,  so  that  those 
rays  farthest  from  the  optical  axis  are  least  deviated  by  it. 

3.  The  anterior  and  posterior  curvatures  of  the  lens  are  cor- 
rective of  each  other.     4.  The  power  of  refraction  of  the  lens 


VISION. 


573 


does  not  increase  regularly  from  the  center  to  the  circumfer- 
ence. 

Astigmatism. — In  this  defect  the  vertical  meridian  is  sup- 
posed to  be  more  convex  than  the  horizontal,  as  is  partially 
the  case  with  the  cornea  of  the  eye,  and  it  is  to  this  body  that 
astigmatism  is  usually  referable,  rather  than  to  the  lens,  though 
the  latter  may  also  be  defective. 

In  astigmatism,  when  a  vertical  line  is  in  focus  a  horizontal 
can  not  be  distinctly  seen,  and  the  reverse.  This  any  one 
may  readily  demonstrate  to  himself  by  drawing  one  straight 
line  at  right  angles  to  the  center  of  another  and  looking  at  the 
figure ;  when  the  one  is  seen  distinctly,  the  other  is  blurred.  It 
is  to  be  borne  in  mind  that,  in  order  to  see  a  horizontal  line 
distinctly,  it  is  of  most  importance  that  the  rays  that  diverge 
from  this  line,  in  a  series  of  vertical  planes,  be  well  focused, 
rather  than  those  which  diverge  in  the  plane  of  the  line  itself ; 
so  that,  when  the  cornea  is  most  curved  in  the  vertical  meridian, 
a  horizontal  line  will  be  represented  by  an  image  of  a  horizontal 
line  at  the  nearer  focus — i.  e.,  when  the  vertical  is  the  most  con- 
vex meridian,  horizontal  lines  are  soonest  focused,  and  this 
holds,  in  fact,  of  most  eyes. 

When  the  astigmatism  affects  several  meridians,  "  irregular 
astigmatism  "  results. 

The  defect  in  question  is  to  be  corrected  by  glasses  made  of 
sections  of  a  cylinder,  thickest  in  the  region  corresponding  to 
that  of  greatest  corneal,  etc.,  defect. 

Chromatic  Aberration. — In  the  figure  below,  in  which  li  h  rep- 
resents tlie  lens,  it  will  be  seen  that  the  violet  and  red  rays 
have  different  foci,  so  that,  when  the  eye  is  accommodated  for 
the  one  set  of  rays,  the  others  are  seen  indistinctly.     Assuming 


Fio.  415.— Diagram  to  illustrate  chromatic  aberration  (after  Foster). 


that  the  retina  is  at/,  the  rays  will  be  blended;  but  if  between 
V  'dxulf,  or/ and  R,  the  blue  center  will  have  a  red  circumfer- 
ence, and  the  reverse  respectively. 

A.s  the  focal  distances  for  near  objects  differs  so  little  usual- 
ly, this  defect  is  not  observed  by  us ;  but  it  may  be  made  ob- 


574  ANIMAL  PHYSIOLOGY. 

vious  by  looking  at  a  flame  through  cohalt-blue  glass,  which 
allows  only  the  red  and  blue  rays  to  pass  :  the  flame  may  appear 
red  surrounded  by  blue  or  blue  surrounded  by  red,  according 
to  the  character  of  the  accommodation  of  the  eye  at  the  time. 
Since  the  eye  has  to  be  accommodated  for  violet  (see  Fig.  415) 
more  than  blue,  bodies  of  equal  size,  red  in  color,  always  appear 
nearer  than  violet  ones.  Hence,  also,  it  is  difiicult  to  see  the 
red  and  violet  of  the  spectrum  with  equal  distinctness  at  the 
same  time. 

Entoptie  Phenomena. — Opaque  bodies  in  any  of  the  media  of 
the  eye  may  cast  shadows  on  the  retina. 

When  movable,  as  they  often  are  in  the  vitreous  humor, 
they  are  known  as  muscce,  volifantes,  from  their  fancied  resem- 
blance to  gnats. 

One  looking  through  a  microscope  is  apt  at  first  to  see  what 
does  not  exist,  apart  from  his  own  eye,  owing  to  various  forms 
of  the  nature  now  referred  to,  but  which  may  be  distinguished 
from  real  objects  by  the  inability  to  fix  them  in  the  field  of 
vision,  for  as  soon  as  the  attempt  is  made  they  vanish. 

Tears  on  the  cornea  and  other  inequalities  from  foreign 
bodies,  pressure,  etc.,  likewise  give  rise  to  such  phenomena. 

An  interesting  little  experiment,  which  illustrates  both  the 
alterations  in  size  of  one's  own  pupils  with  the  amount  of  light, 
and  at  the  same  time  irregularities  in  their  margins,  if  they 
exist,  may  be  thus  carried  out :  Let  a  pin-hole  be  pricked  in  a 
card,  and,  holding  this  close  to  the  eye,  look  at  a  light  or  a 
bright  surface.  On  opening  and  closing  the  other  eye  the 
changes  in  the  size  of  the  pupil  of  the  first  eye  may  be  seen 
to  alter  with  the  amount  of  light  admitted  to  the  second — i.  e., 
the  field  of  view  is  alternately  diminished  and  increased. 

Anomalies  of  Refraction. — 1.  We  may  speak  of  an  eye  in  which 
the  refractive  power  is  such  that,  under  the  limitations  referred 
to  before  (page  564),  images  are  focused  on  the  retina,  as  the 
emmetropic  eye.  The  latter  is  illustrated  by  Fig.  416.  In  the 
upper  figure,  in  which  the  eye  is  represented  as  passive  (nega- 
tively accommodated),  parallel  rays— i.  e.,  rays  from  objects 
distant  more  than  about  seventy  yards  (according  to  some 
writers  much  less) — are  focused  on  the  retina ;  but  those  from 
objects  near  at  hand,  the  rays  from  which  are  divergent,  are 
focused  behind  the  retina.  In  the  lower  figure  the  lens  is  rep- 
resented as  more  bulging,  from  accommodation,  as  such  diver- 
gent rays  are  properly  focused. 

2.  In  the  myopic  (near-sighted)  eye  the  parallel  rays  cross 


VISION. 


575 


within  the  vitreous  humor,  and  diffusion-circles  being  formed 
on  the  retina,  the  image  of  the  object  is  necessarily  blurred, 


Pi*^i 


Fig.  416.— Diazrams  to  illustrate  conditions  of  refraction  in  normal  eye  when  unaccommo- 
dated (passive,  or  negatively  accommodated),  and  when  accommodated  for  "near" 
objects  (after  Landois). 

so  that  an  object  must,  in  the  case  of  such  an  eye,  be  brought 
unusually  near,  in  order  to  be  seen  distinctly — i.  e.  the  near 


■--/--z'-- 


Fio.  417.  —Anomalies  of  refraction  in  a  myopic  eye  (after  Landois). 


point  is  abnormally  near  and  the  far  point  also,  for  parallel 
rays  can  not  be  focused ;  so  that  objects  must  be  near  enough 
for  the  rays  from  them  that  enter  the  eye  to  be  divergent. 

The  myopic  eye  is  usually  a  long  eye,  and,  though  the 
mechanism  of  accommodation  may  be  normal,  it  is  not  so 
usually,  tlie  ciliary  muscle  being  frequently  defective  in  some 
of  its  fibers,  which  may  be  either  hypertrophied  or  atrophied,  or 
with  some  affected  one  way  and  others  in  the  opposite.  More- 
over, there  is  also  generally,  in  bad  cases,  "  spasm  of  accommo- 
dation "  (i.  e.,  of  the  ciliary  muscle),  with  increased  ocular 
tension,  etc.  The  remedies  are,  rest  of  the  accommodation 
merhanism  and  the  use  of  concave  glasses. 

3.  The  opposite  defect  is  hyperinetropia.   The  hypermetropic 


576  ANIMAL  PHYSIOLOGY. 

eye  (Fig.  418),  being  too  short,  parallel  rays  are  focused  be- 
hind the  retina ;  hence  no  distinct  image  of  distant  objects  can 


Fig.  418.— Anomalies  of  refraction  in  the  hypermetropic  eye  (after  Landois). 

be  formed,  and  they  can  only  be  seen  clearly  by  the  use  of  con- 
vex glasses,  except  by  the  strongest  efforts  at  accommodation. 
When  the  eye  is  passive,  no  objects  are  seen  distinctly  beyond 
a  certain  distance — i.  e.,  the  7iear  point  is  abnormally  distant 
(eight  to  eighty  inches).  The  defect  is  to  be  remedied  by  the 
nse  of  convex  glasses. 

4.  Presbyopia,  resulting  from  the  presbyopic  eye  of  the  old, 
is  owing  to  defective  focusing  power,  partly  from  diminished 
elasticity  (and  hence  flattening)  of  the  lens,  but  chiefly,  proba- 
bly, to  weakness  of  the  ciliary  muscle,  so  that  the  changes 
required  in  the  shape  of  the  lens,  that  near  objects  may  be  dis- 
tinctly seen,  can  not  be  made.  The  obvious  remedy  is  to  aid 
the  weakened  refractive  power  by  convex  glasses.  It  is  prac- 
tically important  to  bear  in  mind  that,  as  soon  as  any  of  these 
defects  in  refractive  power  (though  the  same  remark  applies 
to  all  ocular  abnormalities)  are  recognized,  the  remedy  should 
be  at  once  applied,  otherwise  complications  that  may  be  to  a 
large  extent  irremediable  may  ensue. 

Visual  Sensations. 

We  have  thus  far  considered  merely  what  takes  place  in  the 
eye  itself  or  the  physical  causes  of  vision,  without  reference  to 
those  nervous  changes  which  are  essential  to  the  perception  of 
an  object.  It  is  true  that  an  image  of  the  object  is  formed  on 
the  retina,  but  it  would  be  a  very  crude  conception  of  nervous 
processes,  indeed,  to  assume  that  anything  resembling  that 
image  were  formed  on  the  cells  of  the  brain,  not  to  speak  of 
the  superposition  of  images  inconsistent  with  that  clear  mem- 
ory of  objects  we  retain.     Before  an  object  is  "  seen,"  not  only 


VISION. 


577 


must  there  be  a  clear  image  formed  on  the  retina,  but  impulses 
generated  in  that  nerve  expansion  must  be  conducted  to  the 
brain,  and  rouse  in  certain  cells  there  peculiar  molecular  condi- 
tions, upon  which  the  perception  finally  depends. 

For  the  sake  of  clearness,  we  may  speak  of  the  changes 
effected  in  the  retina  as  sensory  impressions  or  impulses,  which, 
when  completed  by  corresponding  changes  in  the  brain,  develop 
into  sensations,  which  are  represented  psychically  by  percep- 
tions;  hence,  though  all  these  have  a  natural  connection,  they 
may  for  the  moment  be  considered  separately.  It  is  as  yet 
beyond  our  power  to  explain  how  they  are  related  to  each 
other  except  in  the  most  general  way,  and  the  manner  in 
which  a  mental  perception  grows  out  of  a  physical  alteration 
in  the  molecules  of  the  brain  is  at  present  entirely  beyond 
human  comprehension. 


Fio.  419. 


Fio.  420. 


Fm.  419.— Wrtical  H»-fti<in  of  rftina  fafter  H.  Mnilcr).     1.  layi-r  of  rods  and  coni's  ;  a,  rods; 

3.  coriMi :  4.  5.  f).  ••xternal  jframilc  laytr  ;  7,  intt-rnal  praniilf  lavt-r  ;  9,  10,  fliii-ly  (framilar 
,.     *f?>'  '*/''''  •  "■  ^^y*"^  "^  nervcc-ellH  :  12.  14,  fibcpH  of  optic  iitrvc';  ID,  iru-mhraiia  liiriitaiis. 
-  lo    4!fll.-4,'oniiectiori  of   rod.s  and  cont'S  of   retina  with  ncrvouH  elcnii-nts  (after  Sappt-y). 

1,  2,  3.  rodH  and  eones  Heen  from  iu  front ;  4,  5,  0,  Bide  view.    The  rest  will  be  clear  from 

the  preceding  tlirnre. 


linK  fli^ire. 

87 


578 


ANIMAL  PHYSIOLOGY. 


Affections  of  the  Retina. — There  is  no  doubt  that  the  fibers  of 
the  optic  nerves  can  not  of  themselves  be  directly  affected  by- 
light.  This  may  be  experimentally  demonstrated  to  one's  self 
by  a  variety  of  methods,  of  which  the  following  are  readily  car- 
ried out :  1.  Look  at  the  circle  (Fig.  421)  on  the  left  hand  with  the 


Fig.  431  (after  Bernstein). 

right  eye,  the  left  being  closed,  and,  with  the  page  about  twelve 
to  fifteen  inches  distant,  gradually  approximate  it  to  the  eye, 
when  suddenly  the  cross  will  disappear,  its  image  at  that  dis- 
tance having  fallen  on  the  blind-spot,  or  the  point  of  entrance 
of  the  optic  nerve.  2.  Fixing  the  eye  as  before  on  a  mark  on 
a  sheet  of  white  paper  made  by  a  pen,  draw  the  latter  outward 
till  its  point  disappears  from  view.  Mark  the  location  of  the 
pen-point  when  this  occurs,  and  continue  the  movement  till  it 
again  appears.  Mark  this  point  also.  This  process  may  be 
continued  in  other  directions  besides  the  horizontal,  and,  by 
joining  these  points,  an  irregular  outline  is  formed,  marking 
off  a  portion  of  the  "  visual  field,"  within  which  there  is  really 
no  vision.  3.  A  small  image  from  a  flame  projected  on  the 
blind-spot  by  a  mirror  is  not  visible,  though  readily  perceived 
when  it  falls  on  the  retina  proper. 


Fig.  422.— Diagrrammatic  section  of  macula  lutea  (after  Huxley),  a,  a,  pigment  of  choroid  ; 
b,  c,  rods  and  cones  ;  d,  d,  outer  granular  or  nuclear  layer  ;  /,  /,  inner  granular  layer ; 
gf,  3,  molecular  layer  ;  h,  h,  layer  of  nerve-cells  ;  i,  i,  fibers  of  optic  nerve. 

It  remains,  then,  to  determine  what  part  of  the  retina  is 
affected  by  light.     The  evidence  that  it  is  the  layers  of  rods 


VISION. 


579 


and  cones  is  convincing.  If  it  could  be  shown  that  parts  of 
the  retina  itself  internal  to  these  layers  cast  2)erceptihle  shad- 
ows, the  conclusion  that  the  rods  and  cones  are  the  essential 
parts  of  the  sensory  organ  would  be  inevitable.  The  following 
experiment  proves  this :  When  a  light  is  moved  backward  and 
forward  (to  prevent  retinal  fatigue)  before  the  eye,  so  that  the 
rays  from  it  enter  the  organ,  while  the  subject,  standing  in  a 
dark  room,  gazes  toward  a  plain-colored  wall,  his  accommoda- 
tion being  relaxed,  he  will  behold  radiating  shadows,  somewhat 
suggestive  of  the  leafless  branches  of  an  old  tree.  These  cor- 
respond with  the  picture  of  the  retinal  vessels  as  ascertained 
by  an  examination  of  the  eye  with  the  ophthalmoscope.  Some 
persons  always  see  the  shadows  of  the  blood-corpuscles  also; 
and,  in  fact,  one  physiologist  has,  by  observing  these,  calculated 
the  rate  of  the  blood-flow  in  the  retinal  vessels.     Instead  of 


Fig.  42-4. 


Fig.  423. 

Fio.  423.— Ophthalmoscopic  picture  of  fundua  oculi,  showing  the  g:enprally  red  ground  Mark 
in  figure),  im  which  may  he  distinguished  the  point  of  entrance  of  optic  nerve,  in  the 
region  of  which  the  prominent  vessels  may  be  seen  to  arise  (after  Bernstein). 

Fio.  4a<.— I>iafrrani  to  explain  experiment  to  get  Purkinje's  figures.  In  this  case  the  light 
paj<s<'s  through  the  lens,  an  image  is  formed  on  the  retina,  and  the  light  is  reflected  from 
this  image  to  another  f)art  of  the  retina,  at  which,  being  le.ss  illuminated,  the  shadows  of 
the  retinal  vessels  are  more  readily  perceived.  Thus,  supjiose  the  candle  to  be  held  at  a, 
\tH  image  will  te  formed  at  h  and  reflected  to  c,  at  which  puint  shadows  appear  and  are 
proje(;t«-d  \n\/t  the  visual  field  at  d.  By  moving  the  candle  to  «',  we  get  new  relative  posi- 
tions for  image,  vessels,  etc.  (after  Bernstein). 


moving  the.  light  tf)  and  fro,  it  may  be  concentrated  for  a  few 
seconds  }>y  a  lens  with  the  same  result — the  appearance  of 
Purkinje's  figures,  as  they  are  termed.  When  the  light  is 
moved,  tlicy  shift  ])lace  cf)rrespondingly.  If  the  sensory  parts 
were  not  situated  behind  tlie  retinal  vessels,  it  is  impossible  to 
f'onceive  how  tlieir  shadows  could  be  seen,  and  certain  mathe- 


580  ANIMAL  PHYSIOLOGY. 

matical  calculations,  based  on  data  derived  from  tlie  experi- 
ment just  described,  locate  the  part  concerned  in  tbe  layer  of 
rods  and  cones.  Putting  together  all  the  facts  of  experiment 
with  those  derived  from  pathological  conditions,  there  seems 
to  be  no  reasonable  doubt  that  the  rods  and  cones  of  the  retina 
are  the  seat  of  origin  of  the  visual  impulses. 

The  performance  of  the  experiment  as  given  above  requires 
usually  two  persons,  but  there  are  simpler  methods,  which,  in 
some  cases,  also  bring  out  the  figures  more  satisfactorily:  (1) 
It  often  suffices  to  move  the  head  back  and  forward  before  the 
tube  of  a  microscope  without  its  objective ;  or  (2)  to  move  rapidly 
a  card  with  a  pin-hole  held  close  before  the  eye,  while  the  sub- 
ject gazes  at  a  bright  clear  sky.  When  the  card  is  moved  from 
side  to  side,  the  vertical  vessels  are  seen ;  if  up  and  down,  the 
horizontal.  The  shadows  of  the  capillaries  come  out  especially 
well  by  this  method.  It  is  essential,  however,  whatever  plan 
be  adopted,  to  gaze  into  infinite  distance,  as  it  were,  in  order 
fully  to  relax  the  accommodation  and  to  avoid  excessive  ex- 
pectancy, which  frustrates  the  former  attempts  at  relaxation. 

The  Nature  of  the  Processes  which  originate  Visual  Impulses. — 
Much  interest  attached  at  one  time  to  visual  imrple  (rhodop- 
sin),  because  it  was  hoped  that  it  might  furnish  a  chemical  ex- 
planation of  vision.  It  was  found  that  in  certain  animals,  as 
frogs,  when  kept  in  darkness,  the  visual  purple  was  renewed 
after  having  been  bleached  out  by  exposure  to  light ;  indeed  an 
exact  "  optogram,"  or  picture  of  an  object,  might  be  made  and 
by  appropriate  reagents  fixed  on  the  retina  as  a  bleached  part 
of  the  visual  purple. 

This  substance  is  found  exclusively  in  the  outer  limbs  of  the 
rods  and  not  at  all  in  the  cones ;  but,  since  the  retinas  of  some 
animals  (snakes)  are  destitute  of  rods,  and  visual  purple  is  also 
wanting  in  the  macula  lutea  and  fovea  centralis  of  man  and 
the  apes,  the  points  of  greatest  retinal  sensibility,  it  is  manifest 
that  the  theory  based  upon  its  presence  breaks  down  as  an  ex- 
planation of  vision,  if  to  be  applied  universally ;  besides,  the 
retinas  of  some  animals  with  rods  (dove,  hen,  bat)  are  entirely 
devoid  of  visual  purple. 

But,  though  this  particular  method  of  application  of  chem- 
istry to  the  explanation  of  the  origin  of  retinal  impulses  has 
failed,  it  does  not  follow  that  a  chemical  theory  as  such  is  false, 
though  it  must  be  admitted  that  the  evidence  is  as  yet  very 
incomplete  on  which  to  found  such  an  explanation. 

But  when  we  consider  the  evolution  of  the  eye,  and  examine 


VISION.  581 

into  the  facts  of  comparative  anatomy  and  physiology,  there 
are  many  of  a  significance  that  we  can  not  ignore ;  the  impor- 
tance of  light  to  most  protoplasmic  processes,  such  as  the  ac- 
cumulation of  pigment  in  certain  regions  marking  the  very 
beginnings  of  eyes ;  the  large  amount  of  pigment  found  in  the 
eyes  of  most  groups  of  animals  and  of  nearly  all  mammals  sug- 
gesting that  this  is  a  provision  for  the  retention  of  light,  which 
we  can  scarcely  conceive  as  acting  in  other  than  a  chemical 
manner.  At  the  same  time,  in  keeping  with  the  spirit  of  this 
work  throughout,  we  suggest  caution  in  believing  that  explana- 
tions based  on  our  limited  experience  are  the  only  ones  possible. 

It  is  worth  while  to  bear  in  mind,  however,  that  currents  of 
rest  and  currents  of  action  similar  to  those  demonstrated  to 
exist  in  muscle,  glands,  nerves,  etc.,  may  be  shown  to  exist  in 
the  retina.  In  all  the  other  cases  these  are  in  intensity  parallel 
to  the  degree  of  functional  (and  chemical)  activity  of  the  part, 
and  it  makes  the  probability  of  there  being  a  chemistry  of  the 
retina  as  a  foundation  for  the  impulses  therein  generated  great- 
er. The  subject  is  as  yet,  however,  in  the  region  rather  of 
speculation  than  of  ascertained  fact. 

The  Laws  of  Retinal  Stimulation. — It  may  be  noticed  that,  when 
a  circular  saw  in  a  mill  is  rotated  with  extreme  rapidity,  it  seems 
to  be  at  rest. 

If  a  stick  on  fire  at  one  end  be  rapidly  moved  about,  there 
seems  to  be  a  continuous  fiery  circle. 

If  a  top  painted  in  sections  with  various  colors  be  spun,  the 
different  colors  can  not  be  distinguished,  but  there  is  a  color 
resulting  from  the  blending  of  the  sensations  from  them  all, 
which  will  be  white  if  the  spectral  colors  be  employed. 

When,  on  a  dark  night,  a  moving  animal  is  illuminated  by 
a  flash  of  lightning,  it  seems  to  be  at  rest,  though  the  attitude 
is  one  we  know  to  be  appropriate  for  it  during  locomotion. 

It  becomes  necessary  to  explain  these  and  similar  phe- 
nomena. Another  observation  or  two  will  furnish  the  data  for 
the  solution. 

If  on  awakening  in  the  morning,  when  the  eyes  have  been 
well  rested  and  the  retina  is  therefore  not  so  readily  fatigued, 
one  looks  at  the  window  for  a  few  seconds  and  then  closes  the 
eyes,  he  may  perceive  that  the  picture  still  remains  visible  as 
a  pofiiiive  after-irnage  ;  while,  if  a  light  be  gazed  upon  at  night 
and  the  eyes  suddenly  <^]os(;d,  an  after-image  of  tlie  light  may 
be  observed. 

It  thus  appears,  then,  that  the  impression  or  sensation  out- 


582  ANIMAL   PHYSIOLOGY. 

lasts  the  stimulus  in  these  cases,  and  this  is  the  explanation 
into  which  all  the  above-mentioned  facts  fit.  When  the  fiery- 
point  passing  before  the  eyes  in  the  case  of  the  fire-brand  stimu- 
lates the  same  parts  of  the  retina  more  frequently  than  is  con- 
sistent with  the  time  required  for  the  previous  impression  to 
fade,  there  is,  of  necessity,  a  continuous  sensation,  which  is  in- 
terpreted by  the  mind  as  referable  to  one  object.  In  like  man- 
ner, in  the  case  of  a  moving  object  seen  by  an  electric  flash,  the 
duration  of  the  latter  is  so  brief  that  the  object  illuminated  can 
not  make  any  appreciable  change  of  position  while  it  lasts ;  a 
second  flash  would  show  an  alteration,  another  part  of  the  retina 
being  stimulated,  or  the  original  impression  having  faded,  etc. 

In  the  case  of  a  top  or  (better  seen)  color-disk,  painted  into 
black  and  white  sectors,  it  may  be  observed  that  with  a  faint 
light  the  different  colors  cease  to  appear  distinct  with  a  slower 
rotation  than  when  a  bright  light  is  used.  The  variation  is 
between  about  ^V  ^^'^  to  of  a  second,  according  to  the  intensity 
of  the  light  used.  Fusion  is  also  readier  with  some  colors  than 
others. 

It  is  a  remarkable  fact  that  one  can  distinguish  as  readily 
between  the  quantity  of  light  emanating  from  10  and  11  can- 
dles as  between  100  and  110.  Weber's  law  is  a  highly  general- 
ized form  of  this  statement  applicable  to  all  the  senses. 

But  with  vision,  as  with  all  the  senses,  a  lower  and  espe- 
cially an  upper  limit  is  soon  reached,  within  which  alone  we 
can  discriminate.  It  is  not  possible  to  distinguish  between  the 
difference  in  brightness  of  the  central  and  the  circumferential 
parts  of  the  sun,  though  it  is  known  that  the  actual  difference 
is  very  great,  while  it  is  easy  enough  to  recognize  a  marked 
difference  in  the  light  of  a  room  when  two  candles  are  used  in- 
stead of  one.  Within  certain  limits  we  can  appreciate  a  differ- 
ence in  illuminating  power  of  about  jw  of  a  given  total. 

The  Visual  Angle. — If  two  points  be  marked  out  with  ink  on 
a  sheet  of  white  paper,  so  close  together  that  they  can  be  just 
distinguished  as  two  at  the  distance  of  12  to  20  inches,  then  on 
removing  them  a  little  farther  away  they  seem  to  merge  into 
one. 

The  principle  involved  may  be  stated  thus  :  When  the  dis- 
tance between  two  points  is  such  that  they  subtend  a  less  visual 
angle  than  60  seconds,  they  cease  to  be  distinguished  as  two. 
Fig.  425  illustrates  the  visual  angle.  It  will  be  noticed  that  a 
larger  object  at  a  greater  distance  subtends  the  same  visual 
angle  as  a  smaller  one  much  nearer.     The  size  of  the  retinal 


VISION. 


58J 


image  corresponding  to  GO  seconds  is  '004  mm.  (4  /x),  and  this 
is  about  tlie  diameter  of  a  single  rod  or  cone.     It  is  not,  how- 


FiG.  4^.— The  visual  angle.    The  object  at  A"  appears  no  larger  than  the  one  at  ^  iLe  Conte). 

ever,  true  that  when  two  cones  are  stimulated  two  objects  are 
inferred  to  exist  in  every  case  by  the  mind ;  for  the  retina 
varies  in  different  parts  very  greatly  in  general  sensibility  and 
in  sensibility  to  color. 

It  is  noticeable  that  visual  discriminative  power  can  be 
greatly  improved  by  culture,  a  remark  which  applies  especially 
to  colors.  It  seems  altogether  probable  that  the  change  is  cen- 
tral in  the  nerve-cells  of  the  part  or  parts  of  the  brain  con- 
cerned, especially  of  the  cortical  region,  where  the  cell  processes 
involved  in  vision  are  finally  completed. 

Color-Sensations. — As  this  subject  is  still  in  a  very  unsettled 
condition,  it  will  be  well  in  discussing  it  to  keep  the  facts  of 
physiology  and  of  physics  distinct  from  each  other  and  from  the 
theories  proposed  to  account  for  them. 

It  is  rare  to  see  in  nature  the  pure  colors  of  the  spectrum ; 
more  frequently  the  reds,  blues,  etc.,  we  behold  are  the  corre- 
sponding colors  of  the  spectrum,  with  the  addition  of  a  variable 
quantity  of  white  light.  In  the  spectrum  itself  there  is  an 
unlimited  number  of  shades,  not  usually  specially  noticed,  in- 
termediate between  the  main  colors. 

Hence  we  may  regard  a  color  as  dependent  on  (1)  the  wave- 
length of  its  constituent  rays ;  (2)  on  the  quantity  of  the  par- 
ticular light  falling  on  the  retina ;  and  (3)  on  the  quantity  of 
white  light  mixed  with  this.  When  no  white  light  at  all  enters, 
the  color  is  said  to  be  saturated,  such  being  heavy  and  aestheti- 
cally unattractive;  when  much  of  such  light,  bright,  etc.  A 
gray  results  from  a  certain  mixture  of  white  with  Idack  ;  the 
browns  by  fusion  of  red,  yellow,  white,  and  black.  But  in  this 
and  all  other  instances  in  which  we  speak  of  "  fusion,"  "  blend- 
ing," "  mixture,"  etc.,  we  refer  to  physioUxjical  blending  owing 
to  contemporaneous  stimulation  by  light  of  diff(!rent  wave- 
lengths. Thus,  orange  results  from  the  action  of  the  red  and 
yellow  rays  at  the  same  time,  and  can  not  be  produced  by  any 


584  ANIMAL   PHYSIOLOGY. 

mixture  of  the  wave-lengths  of  red  and  yellow.  Again^  certain 
colors  known  as  complevientary  by  psychic  fusion  gave  rise 
to  white,  though  no  physical  mixture  of  such  colored  pig- 
ments will  produce  white.  These  are  red  and  blue-green;, 
orange  and  blue;  yellow  and  indigo-blue;  green-yellow  and 
violet. 

Now,  when  a  child  beholds  orange,  he  has  not  the  faintest 
idea  that  it  is  related  to  red,  or  that  white  can  be  in  any  way 
produced  from  any  combination  of  colors,  any  more  than,  when 
he  hears  a  perfect  musical  chord,  has  he  any  idea  of  its  being 
produced  by  the  simultaneous  production  of  its  component 
notes.  To  him  both  the  colors  and  the  chord  are  independent 
facts.  But  by  simple  experiments  their  origin  may  be  illus- 
trated. As  regards  comple- 
mentary colors,  Lambert's  ex- 
periment may  easily  be  per- 
formed :  Place  a  red  wafer  (or 
a  slip  of  paper)  on  a  sheet  of 
white  paper,  and  about  three 
\  inches  behind  it  a  blue  one. 

\  Hold    a    plate    of    glass    be- 

— -r? tween  the  two  and  vertically. 


h  d  c 

Fig.  426.— Lambert's  experiment.  The  wafers  ^O  that  whilc  gaziug  at  the 
cal  glass  plate' at  a  (after  Bernstein)^  ^^^ '"  ^^^  Wafcr  through  it  a  re- 
flected image  of  the  blue  one 
will  be  thrown  into  the  eye  in  the  same  direction  as  that  of  the 
red  image,  the  result  being  a  sensation  of  purple. 

As  before  referred  to,  a  rotating  disk  on  which  all  the  colors 
of  the  spectrum  are  represented  in  equal  subdivisions,  when  the 
speed  is  sufficiently  great,  appears  white  from  the  fusion  of  the 
sensations.  Of  course,  instead  of  all  the  colors,  complementary 
ones  suffice.  As  a  matter  of  fact,  we  may  recognize  six  funda- 
mental colors — white,  black,  red,  yellow,  green,  and  blue — and 
these  may  be  the  outcome  of  the  ^physiological  mixture  of  three 
"  standard  "  sensations. 

We  now  proceed  to  matters  of  speculation.  At  the  present 
day  two  theories  to  account  for  color- vision  monopolize  atten- 
tion :  1.  The  Young-Helmholtz  theory  assumes  that  there  are 
only  three  primary  sensations,  or,  in  other  words,  that  the  reti- 
na is  affected  only  by  rays  of  light  corresponding  to  red,  green, 
and  violet  (or  blue) ;  and  the  manner  in  which  any  color  is  pro- 
duced (in  the  mind)  will  appear  from  an  examination  of  Fig. 
427.      Thus,  when  red  is  the  color  seen,  though  the  retinal 


VISION. 


585 


stimiilation  is  not  confined  solely  to  the  rays  of  the  red  end  of 
the  spectrum,  it  is  chiefly  by  these  that  what  we  may  call  psy- 
chic red  is  produced — i,  e.,  the  mental  perception  of  red  is  de- 
pendent on  a  specific  stimulation  of  the  retina  by  rays  of  a  cer- 
tain wave-length,  though  at  the  same  time  there  is  a  feebler 
sensation  of  green  and  violet.     Orange  would  in  like  manner 


Fig.  427.— Illustrates  the  Youngr-Helmholtz  theory  of  color-vision.  The  letters  in  the  lower 
line  indicate  colors  of  spectrum  in  natural  order.  1.  denotes  the  "red'';  2.  "green";  3, 
"violet"  primary-color  sensation.  The  diagram  shows  by  the  height  of  the  curve  in 
each  instance  to'  what  extent  the  primary-color  sensations  are  respectively  excited  by 
vibrations  of  different  wave-lengths  (after  Bernstein). 

result  from  a  large  admixture  of  red,  considerable  of  green,  and 
ver}^  little  of  violet.  2.  Hering's  theory  is  a  chemical  one.  He 
assumes  the  existence  of  three  kinds  of  visual  substances: 
white-black,  yellow-blue,  red-green.  Either  in  the  retina  or 
elsewhere  in  the  eye  it  is  believed  that  two  processes  are  in  con- 
stant operation,  the  opposite  of  each  other,  and  which  corre- 
spond to  the  changes  assumed  to  take  place  in  protoplasm 
generally,  and  to  which  we  have  referred  already  as  ana- 
bolism  and  katabolism,  or  construction  (assimilation)  and  de- 
struction (dissimilation).  When  dissimilation  is  in  excess,  the 
lighter  colors  result — white,  yellow,  red  ;  and  the  others  when 
assimilation  prevails.  Orange  would  be  seen  when  red  and 
yellow  are  simultaneously  produced — i.  e.,  when  the  red-green 
and  yellow-blue  substances  both  undergo  dissimilation  to  a 
degree  in  excess  of  its  opposite  phase. 

One  test  of  these  theories  would  be  their  application  to  ex- 
])laiM  thf  deff'ct  next  to  be  mentioned. 

Color-BIindneBS. — There  are  all  degrees  of  this  defect,  from 
such  as  exists  in  every  eye — i.  e.,  inability  to  perceive  color 
equally  well  by  all  parts  of  the  retina,  to  complete  loss  of  the 
faculty  of  discriminating  color  at  all. 

1.  ComplAf  (■olor-hlindness  (achromatopsy)  is  marked  by 
inability  to  distinguish  any  colors,  the  spectrum  being  brightest 


586  ANIMAL   PHYSIOLOGY. 

in  the  middle,  but  any  picture  appears  as  a  photograph.     It 
may  be  unilateral. 

2.  Yellow-Blue  Blindness. — The  spectrum  presents  only  red 
and  green,  and  hence  is  usually  much  shortened.  It  is  occa- 
sionally unilateral. 

3.  Bed- Green  Blindness  (Daltonism). — Yellow  and  blue  may 
be  discriminated,  violet  and  blue  seem  alike,  and  red  and  green 
practically  do  not  exist. 

It  is  to  be  borne  in  mind  that  it  is  very  difficult  to  ascer- 
tain the  exact  condition  of  color-blind  persons,  from  their  in- 
ability to  communicate  their  state  of  mind.  They  often  make 
discriminations  apparently  based  on  color  distinctions,  but,  in 
reality,  on  the  form,  texture,  position,  etc.,  of  objects.  It  is 
also  all  but  impossible  to  be  precisely  certain  as  to  the  extent 
to  which  the  lower  animals  can  distinguish  between  colors. 

To  apply  the  above  theories  of  color-vision  to  the  explana- 
tion of  color-blindness :  In  the  case  of  red-green  blindness,  ac- 
cording to  the  Young-Helmholtz  explanation,  there  is  the  ab- 
sence of  one  of  the  primary  sensations  (red),  so  that  the  colors 
seen  are  the  result  of  mixtures  of  the  other  two  primary  sensa- 
tions. What  we  call  yellow  must  be  to  the  subject  of  this 
defect  a  bright  green.  According  to  Hering's  theory  such 
persons  lack  the  red-green  substance ;  hence  their  color- vision 
must  be  limited  to  mixtures  of  yellow  and  blue  alone.  But,  if 
blindness  to  red  and  green  can  exist  separately,  as  has  been  as- 
serted, this  theory  fails  to  explain  it,  though  the  former  would ; 
while  total  color-blindness  is  explicable  by  Hering's  theory, 
but  not  by  the  rival  one.  It  is  probable  that  neither  is  broad 
enough  to  meet  the  facts,  even  if  correct  in  principle.  They 
serve  the  end  of  being  provisional  hypotheses  till  better  are 
found. 

Psychological  Aspects  of  Vision. 

It  is  impossible  to  ignore  entirely,  in  treating  of  the  physi- 
ology of  the  senses,  the  mind,  or  perceiving  ego. 

By  virtue  of  our  mental  constitution,  we  refer  what  we 
"  see  "  to  the  external  world,  though  it  is  plain  that  all  that  we 
perceive  is  made  up  of  certain  sensations. 

We  recognize  the  "  visual  field "  as  that  part  of  the  outer 
world  within  which  alone  our  vision  can  act  at  any  one  time ; 
and  this  is,  of  course,  smaller  for  one  than  for  both  eyes. 

If  one  takes  a  large  sheet  of  paper  and  marks  on  its  center 
a  spot  on  which  one  or  both  eyes  are  fixed,  by  moving  a  point 


VISION.  587 

lip  or  down,  to  tlie  right  or  the  left,  he  may  ascertain  the  limits 
of  the  visual  field  for  a  plane  surface.  The  visual  field  for 
both  eyes  measures  about  180°  in  the  horizontal  meridian;  for 
one  eye  about  145° ;  and  in  the  vertical  meridian  100°. 

Imperfections  of  Visual  Perceptions. — We  may  now  consider 
some  defects  which  we  know  to  exist  by  the  use  of  our  reason- 
ing powers  in  the  mental  perception  we  form  of  objects  in  the 
visual  field : 

.1.  Irradiation. — It  is  easy  to  notice  that  a  white  spot  on  a 
dark  ground  appears  larger  than  a  dark  spot  of  equal  size  on 
a  white  ground.     This  has  been  spoken  of  as  the  result  of 


Fig.  428. — Illustrates  irradiation.    The  ^vliite  patch  in  the  dark  ground  seems  larger  than  the 
dark  one  iu  the  light  ground  (after  Bernstein). 

irradiation — a  sort  of  overflow  of  sensation,  though  whether 
to  be  referred  to  the  retina  or  to  the  brain-areas  concerned  is 
uncertain. 

2.  Contrast. — When  a  white  strip  of  paper  is  laid  between 
two  black  ones,  the  center  of  the  white  strip  is  not  so  bright  as 
its  edges,  from  contrast ;  and  experiments  illustrating  the  same 
princixjle  may  be  made  with  colored  papei'.  This  law  of  con- 
trast is  very  wide  in  its  application,  and  will  be  referred  to 
later. 

3.  The  Blind-Spot. — It  might  be  supposed  at  first  that  one 
.should  perceive  gaps  in  the  field  of  vision  on  account  of  the 
blind-spot;  but,  when,  it  is  remembered  that  to  see  black  we 
must  have  a  definite  sensation,  and  that  the  mind  places  objects 
lying  on  opposite  sides  of  the  spot  close  together,  the  reason 
that  this  defect  in  structure,  if  such  it  really  be,  is  practically 
inoperative,  becomes  clearer.  It  is  to  be  remembered  that  the 
image  of  an  object  (see  Fig.  432)  never  falls  on  the  blind-spot 
in  both  eyes ;  and,  moreover,  this  area  lies  outside  of  that 
of  greatest  acuteness  {macrda  lutea),  on  which  images  are 
focused. 

The  macula  lutea,  and  e.specially  the  fovea  centralis,  are  the 


588 


ANIMAL  PHYSIOLOGY. 


parts  of  the  retina  most  sensitive  to  both,  form  and  color ;  or, 
to  pnt  it  otherwise,  when  the  retina  is  stimulated  by  an  object, 
whether  colored  or  not,  the  mind  perceives,  becomes  most  read- 
ily cognizant  of  the  sensation,  sees  the  object  best,  when  the 
stimulation  is  confined  to  the  yellow  spot;  and,  as  will  be 
learned  still  more  fully  later,  all  the  arrangements  for  vision 
are  directed  toward  the  focusing  of  the  rays  of  light  that 
emanate  from  objects,  so  that  the  image  may  fall  on  this  region 
of  the  retina. 

In  like  manner,  by  looking  directly  forward,  and  having 
some  one  move  an  object  in  space  as  before,  and  noting  when 
it  ceases  to  be  visible,  an  irregular  figure  of  the  field,  within 
which  vision  is  distinct  in  varying  degrees,  and  beyond  which 
it  is  absolutely  non-existent,  may  be  mapped  out. 

By  using  colored  objects,  as  small  squares  of  paper,  by  the 
above  method,  it  may  be  readily  learned  that  the  field  for  some 
colors  is  much  more  restricted  than  for  others ;  in  fact,  as  such 
an  object  is  moyed  outward,  its  color  seems  to  change :  thus, 
purple  becomes  bluish.  In  all  retinas  there  is  more  or  less 
color-blindness  toward  the  peripheral  parts,  and  this  is  espe- 
cially true  of  red.  The  field  for  the  colors  of  the  spectrum,  etc., 
may  easily  be  shown  to  be  more  limited  than  for  white. 


Fig.  429.— Field  of  color-vision  of  right  eye,  as  projected  by  the  subject  on  the  inner  surface 
of  a  hemisphere,  the  pole  of  which  forms  the  point  of  fixation  for  the  eye  :  semi-diagram- 
matic (after  Nettleship  and  Landolt).  T,  temporal  side  ;  N,  nasal  side  ;  w.  boundary  for 
white  ;  b,  for  blue  ;  r,  for  red  ;  q,  for  green. 


VISION.  589 

Influence  of  the  Pigment  of  the  Macula  Lutea. — If  we  inter- 
pose a  sohition  of  chrome  alum  between  the  eye  and  a  white 
cloud  while  the  general  field  is  purplish,  a  rosy  patch  appears 
in  a  position  corresponding  to  the  yellow  spot.  This  is  owing 
to  the  fact  that  the  solution  allows  only  the  red  and  greenish- 
blue  rays  to  pass,  and,  the  latter  being  absorbed  by  the  yellow 
spot,  we  see  only  the  former  in  the  part  of  the  field  of  vision 
corresponding  to  this  area.  The  experiment  is  also  an  excellent 
one  to  mark  out  the  site  of  the  spot.  Since  the  macula  lutea 
is  the  part  of  the  retina  concerned  in  the  usual  so-called  "  di- 
rect "  vision,  it  will  be  evident  that  what  would  be  yellow  but 
for  the  influence  of  the  pigment  of  this  spot  appears  to  us 
white. 

After-images,  etc. — Positive  after-images  have  already  been 
referred  to ;  but  an  entirely  different  result,  owing  to  exhaus- 
tion of  the  retina,  may  follow  when  the  eye  is  turned  from  the 
object.  If,  after  gazing  some  seconds  at  the  sun,  one  turns  away 
or  merely  closes  the  eyes,  he  may  see  black  suns.  In  like  man- 
ner, when  one  turns  to  a  gray  surface  after  keeping  the  eyes 
fixed  on  a  black  spot  on  a  white  ground,  he  will  see  a  light  spot. 
Such  are  termed  negative  after-images,  and  these  may  them- 
selves be  colored,  as  when  one  turns  from  a  red  to  a  white  sur- 
face and  sees  the  latter  green.  They  may  be  explained  upon 
either  theory  of  color-vision.  According  to  the  theory  of 
Young  and  Helmholtz,  in  the  latter  case  the  green  appears  be- 
cause the  primary  color-sensation  for  red  is  exhausted,  while 
the  others  become  more  prominent  accordingly ;  but  it  is  more 
difficult  to  explain  the  black  suns,  etc.,  by  this  theory,  though 
it  is,  of  course,  open  to  suppose  that  all  the  primary  color-sen- 
sations have  been  exhausted. 

According  to  Hering's  theory,  the  dark  after-images  as  well 
as  the  colored  ones  are  the  result  of  the  preponderance  of  one 
or  the  other  of  the  two  processes  of  assimilation  and  dissimila- 
tion. But,  in  truth,  the  subject  is  very  difficult  of  complete 
solution  at  all  by  the  kind  of  explanations  we  are  at  present 
employing. 

It  is  of  some  importance  to  remember  that  the  retina  is  not 
e<iually  sensitive  to  all  colors.  We  see  the  blues  of  evening 
more  readily  than  the  reds  or  yellows,  hence  the  employment 
of  the  former  extensively  by  artists  in  dej)icting  (evening 
scenes. 

Since  there  is  a  maximum  y)oint  of  stimulation  for  each  main 
color,  it  is  possible  to  und(3rstand  liow,  by  increase  of  the  inteu- 


590 


ANIMAL  PHYSIOLOGY. 


sity  of  its  ligh-t,  one  color  passes  into  another :  e.  g.,  let  violet 
light  be  gradually  increased  in  intensity,  and  the  retina  soon 
fails  to  perceive  this  color  so  strongly ;  but  the  red  and  green 
sensations  being  as  yet  submaximal,  we  perceive  a  color  the 
result  of  the  blending  of  these  two  with  violet,  and  so  on  till 
we  may  get  such  a  mixture  of  the  sensations  of  violet,  red,  and 
green  as  produces  white. 


Fig.  430.— 'When  looked  at  with  one  eye,  the  Hues  are  never  all  distinct  at  one  time ;  this  is  in 
part  owin^  to  astigmatism,  but  in  part  also  to  inability  to  accommodate  perfectly  apart 
from  any  defect  of  this  kind  for  more  than  a  very  limited  area.  When  viewed  with  both 
eyes,  a  number  of  curious  phenomena  may  be  observed,  the  explanation  of  which  we 
leave  the  student  to  work  out  for  himself  (after  Bernstein). 

Misconceptions  as  to  the  Comparative  Size,  etc.,  of  Objects. — A 

glance  at  Figs.  430   and   431  will   illustrate  some   surprising 
peculiarities.     On  a  clear  day  distant  mountains  appear  nearer, 


Fig.  431. — Illustrates  illusions  as  to  size.  In  A  the  height  seems  at  first  greater  than  the 
breadth,  though  they  are  equal ;  the  reverse  in  B  ;  while  C  appears  to  cover  a  less  area 
than  either  of  the  others  (after  Bernstein). 


VISION. 


591 


from  being  seen  better.  The  full  moon  looks  larger  when  near 
the  horizon  than  when  overhead,  from  the  absence  of  objects  in 
the  latter  case  with  which  to  compare  it ;  and  in  like  manner 
distances  on  the  water  or  on  a  vast  plain  seem  less  than  they 
really  are ;  and  so  in  innumerable  instances  the  influence  of  a 
standard  of  comparison  or  its  absence  is  evident. 

Subjective  Phenomena. — When  the  eyelids  are  shut  in  a  dark 
room,  the  eye  does  not  seem  absolutely  devoid  of  light.  Such 
sensation  of  luminosity  as  may  be  feebly  present  is  sometimes 
spoken  of  as  the  "  proper  light  of  the  retina."  When  the  ball 
of  the  eye  is  pressed  upon,  colored  circles  of  light  appear  when 
the  eyes  are  closed,  such  being  plainly  due  to  mechanical  stimu- 
lation of  the  retina.  These  are  "  phosphenes,"  and  are  akin  to  the 
stars  seen  when  the  eye  receives  a  sudden  blow,  or  to  the  sen- 
sations excited  by  electrical  stimulation.  But,  apart  from  any 
stimulation  of  the  retina,  objects  may  apparently  be  seen  in  ex- 
cited conditions  of  the  brain,  as  in  insanity,  delirium  tremens, 
etc.  Sometimes  one  object,  instead  of  being  recognized,  seems 
to  arouse  the  perception  of  another.  The  cause  is  traceable  in 
many  cases  solely  to  the  brain  itself,  especially  the  part  of  the 
cerebral  cortex  concerned  in  vision,  and  illustrates  the  impor- 
tance of  this  part  of  the  central  visual  mechanism,  and  much 
more  into  which  we  can  not  enter  now. 

Co-ordination  of  the  Two  Eyes  in  Vision. 


As  a  matter  of  fact,  we 
are  aware  that  an  object 
may  be  seen  as  one  either 
with  a  single  eye  or  with 
both.  For  binomdar  vis- 
ion it  may  be  shown  that 
the  images  formed  on  the 
two  retinas  must  fall  in- 
variably on  corresponding 
points. 

The  position  of  the  lat- 
ter may  be  gathered  from 
Fig.  4.'}^.  It  will  h(t  noticed 
that  the  malar  side  of  one 
eye  corresponds  to  the  na- 
H(d  Huhi  of  the  other, 
thougli  upper  always  an- 


Fio.  432.— Diapram  to  illustrate  correspondinR  points 
(aft«r  FohUt).  /y,  /i',  li-f'(  Mini  ritclit  eyen  ;  a,  /*,  c, 
are  points  in  one  eye  (;<irrcs|iiiiiiiin(?  to  «],  Z;,,  Cj, 
in  the  other.  The  lower  (ItjiinHare  projections  of 
the  retina  of  the  ri^iit  (/v'l  and  tiio  left  (L)  eye. 
It  may  he  olmerved  that  th(^  malar  side  of  one 
retina  corresponds  to  the  naual  side  of  the  other. 


592 


ANIMAL   PHYSIOLOGY. 


swers  to  upper  and  lower  to  lower.  This  may  also  be  made 
evident  if  two  saucers  (representing  the  fundus  of  each  eye)  be 
laid  over  each  other  and  marked  off,  as  in  the  figure. 

That  such  corresponding  points  do  actually  exist  may  be 
shown  by  turning  one  eye  so  that  the  image  shall  not  fall,  as 
indicated  in  the  figure.  Only  now  and  then,  however,  is  a  per- 
son to  be  found  who  can  voluntarily  accomplish  this,  but  it 
occurs  in  all  kinds  of  natural  or  induced  squint,  as  in  alcohol- 
ism, owing  to  partial  paralysis  of  some  of  the  ocular  muscles. 
We  are  thus  naturally  led  to  consider  the  action  of  these  muscles. 

Ocular  Movements. — Upon  observing  the  movements  of  an 
individual's  eyes,  the  head  being  kept  stationary,  it  may  be 
noticed  that  (1)  both  eyes  may  converge ;  (2)  one  diverge  and 
the  other  turn  inward ;  (3)  both  move  upward  or  downward ; 


Fig.  433. — View  of  the  two  eyes  and  related  parts  (after  Helmholtz). 


(4)  these  movements  may  be  accompanied  by  a  certain  degree 
of  rotation  of  the  eyeball. 

The  eye  can  not  be  rotated  around  a  horizontal  axis  without 
combining  this  movement  with  others.  To  accomplish  the 
above  movements  it  is  obvious  that  certain  muscles  of  the  six 
with  which  the  eye  is  provided  must  work  in  harmony,  both  as 
to  the  direction  and  degree  of  the  movement — i.  e.,  the  move- 
ments of  the  eyes  are  affected  by  very  nice  muscular  co-ordina- 
tions. 


VISION. 


593 


We  may  speak  of  that  position  of  the  eye  when,  with  the 
head  vertical  in  the  standing  position,  the  distant  horizon  is 
viewed    as    the     primary 
position  and  all  others  as 
secondary  positions. 

Fig.  4:34  is  meant  to 
illustrate  diagrammatical- 
ly  the  movements  of  the 
eyeball. 

While  the  several  recti 
muscles  elevate  or  depress 
the  eye,  and  turn  it  inward 
or  outward,  and  the  oblique 
muscles  rotate  it,  the  move- 
ments produced  by  the  su- 
perior and  inferior  recti 
are  always  corrected  by  the 
assistance  of  the  oblique 
muscles,  since  the  former 
tend  of  themselves  to  turn 
the  eye  somewhat  inward. 
In  like  manner  the  oblique 
muscles  are  corrected  by 
the  recti.  The  folio wingtab- 
ular  statement  will  express 
the  conditions  of  muscular 
contraction  for  the  various 
movements  of  the  eye : 


Fig.  434.— Diagram  intended  to  illustrate  action  of 
extrinsic  ocular  muscles  (after  Fick ).  The  heavy 
lines  represent  the  muscles  of  the  eyeball,  and 
the  fine  lines  the  axes  of  movement. 


f  f}lev;itioii Rectus  superior  and  obliquu.s  inferior. 

otraighl  I   j)(.pr(.ssion Rectus  inferior  and  obliquiis  superior. 

move-         )  A,1,lM^.ti\,r.    t,>    ....^...1    ^i.ln            I/nf.fiic    Jntor-Tinc 

ment.« 


Adduction  to  nasal  side.  .  .Rectus  internus. 


I 


Oblique 
move- 
ments. 


Adduction  to  malar  side..  .Rectus  externus. 

Elevation  with  adduction..  Rectus   sui)erior  and   internus,  with  obli- 

quus  inferior. 
Depression  wilh  a<ldu(;tion. Rectus  inferior  and  internus  with  ol)li(iuus 

superior. 
Elevation  with  abduction..  Rectus  superior  and  externus  wilh  ol)li(iuus 

inferior. 
Depression  with  abduct  ion. Rectus  inferior  and  externus,  with  obliquus 

superior. 

What  is  the  nervous  mechanism  by  wliich  these  "associ- 
ated "  movements  of  the  eyes  are  accomi)lished  ?  It  has  been 
foiiiMl,  oxperirrieTitally,  tluit  vvIhmi  diffcrcMit  parts  of  the  corpora 
quadrig(;iiiiria  are  stimulated,  certain   mov(!ments  of  th(;  eyes 

38 


594 


ANIMAL   PHYSIOLOGY. 


follow.     Thus,  stimulation  of  the  right  side  of  the  nates  leads 
to  movements  of  both  eyes  to  the  left,  and  the  reverse  when 

the  opposite  side  is  stimulated ;  also, 
stimulation  in  the  middle  line  causes 
convergence  and  downward  move- 
ment, etc.,  with  the  corresponding 
movements  of  the  iris.  Since  section 
of  the  nates  in  the  middle  line  leads 
to  movements  confined  to  the  eye  of 
the  same  side,  the  center  would  ap- 
pear to  be  double.  However,  it  may  be 
that  the  cells  actually  concerned  do 
not  lie  in  the  corpora  quadrigemina, 
but  below,  or  outside  of  them.  The  localization  is  as  yet  in- 
complete. 

The  Horopter. — If  we  hold  up  one  finger  before  another,  in 
front  of  both  eyes,  when  the  accommodation  is  made  for  the 
one  the  other  will  appear  double,  owing  to  the  images  not  fall- 
ing on  corresponding  parts  of  the  retina;  for,  if  one  eye  be 
closed,  one  of  the  images  disappears. 

Another  way  of  putting  the  matter  is,  to  say  that  the  objects 
in  the  field  under  consideration  do  not  lie  in  the  horopter.     The 


Fig.  435. — Diagram  to  illustrate  de- 
cussation of  fibers  in  the  op- 
tic commissure  of  man  (after 
Flint.) 


Fig.  436.— The  horopter  (after  Le  Conte).    When  the  eyes  are  directed  to  the  point  A  in  the 
circle,  images  from  any  other  part  of  it  (as  D)  fall  on  corresponding  points  of  the  retinae. 


latter  is  that  arrangement  of  points  in  space  from  which  rays 
fall  on  corresponding  (identical)  parts  of  the  retina.     It  must 


VISION..  595 

vary  with  the  position  of  the  eyes,  head,  etc.,  and  often  consti- 
tutes a  very  complex  geometrical  figure  when  the  various 
points  are  united.  The  simj^ler  case  is  when  standing  upright 
we  look  toward  the  distant  horizon,  in  which  instance  the 
horopter  forms  a  plane  drawn  beneath  us — i.  e.,  is  the  ground  on 
which  we  stand.     Tliis  will  appear  from  Fig.  436. 

Estimation  of  the  Size  and  Distance  of  Objects. — The  processes 
by  which  we  form  a  judgment  of  the  size  and  distance  of  objects 
are  closely  related. 

As  we  have  already  shown  (page  583),  the  visual  angle  varies 
both  with  the  size  and  the  distance  of  an  object.  Knowing 
that  two  objects  are  at  the  same  distance  from  the  eye,  we  esti- 
mate that  the  one  is  larger  than  the  other  when  the  image  one 
forms  on  the  retina  is  larger,  or  when  the  visual  angle  it  sub- 
tends is  greater  than  in  the  other  case,  and  conversely.  Thus, 
knowing  that  two  persons  are  at  the  distance  of  half  a  mile 
away,  if  one  is  judged  by  us  to  be  smaller  than  the  other,  it 
will  be  because  the  retinal  image  corresponding  to  the  object 
is  smaller,  other  things  being  equal.  But  the  subject  is  more 
complex  than  might  be  inferred  from  these  statements. 

We  have  already  pointed  out  that  objects  of  a  certain  color 
seem  nearer  than  others ;  also  those  that  are  brighter,  as  in  the 
case  of  mountains  on  a  clear  day.  And  not  only  do  all  the 
qualities  of  the  image  itself  enter  as  data  into  the  construction 
of  the  judgment,  but  numerous  muscular  sensations.  The  eyes 
accommodating  and  converging  for  near  objects,  from  the  law 
of  association,  give  rise  to  the  idea  of  nearness,  for  habitually 
such  takes  place  when  near  objects  are  viewed,  so  that  the 
subject  becomes  very  complex.  That  we  judge  imperfectly  of 
the  position  of  an  object  with  but  one  eye  is  realized  on  attempt- 
ing to  stick  a  pin  into  a  certain  small  spot,  thread  a  needle,  cork 
a  small  bottle,  etc.,  when  one  eye  is  closed. 

Solidity. — By  the  use  of  one  eye  alone  we  can  form  an  idea  of 
the  shape  of  a  solid  body ;  though,  in  the  case  of  such  as  are  very 
complex,  this  process  is  felt  to  be  both  laborious  and  imperfect. 

From  the  limited  nature  of  the  visual  field  for  distinct 
vision,  it  follows  that  we  can  not  with  one  eye  see  equally  dis- 
tinctly all  the  [jarts  of  a  solid  that  is  turncid  toward  us.  After 
a  little  practice  one  may  learn  to  define  for  himself  what  he 
actually  does  see. 

Such  a  figure  as  that  following  results  from  the  combina- 
tioij,  nif^nfally,  of  two  othfirs,  which  answer  to  the  images  fall- 
ing on  the  right  and  on  the  left  eyes  respectively. 


596 


ANIMAL  PHYSIOLOGY. 


In  order  that  such  fusion  shall  take  place,  the  respective 
images  must  fall  on  identical  (corresponding)  parts  of  the  retina. 


71        f\ 71 '^  K 71 

— /  ^\  d/  \  dX 

I  T' 

^  ^ ; ^  a.  Z  a 


Fig.  437.— Illustrates  binocular  vision.  If  the  truncated  pyramid,  P,  be  looked  at  with  the 
head  held  perpendicularly  over  the  figure,  the  image  formed  in  the  right  eye  when  the 
left  is  closed  is  figured  on  the  right,  and  that  seen  when  the  right  eye  is  closed  is  rep- 
resented by  the  figure  in  the  middle.  No  superposition  of  these  figures  will  give  P,  yet 
by  a  pyschic  process  they  are  combined  into  P,  the  figure  as  it  appears  to  both  eyes  (after 
Bernstein). 

As  is  well  known,  the  pictures  used  for  stereoscopes  give 
different  views  of  the  one  object,  as  represented  on  a  flat  sur- 
face. These  are  thrown  upon  corresponding  points  of  the  retina 
by  the  use  either  of  prisms  or  mirrors,  when  the  idea  of  solidity 
is  produced.  As  to  whether  movements  of  the  eyes  (converg- 
ence) are  necessary  for  stereoscopic  vision  is  disputed.  It  has 
been  inferred,  from  the  fact  that  objects  appear  solid  during 
an  electric  flash,  the  duration  of  which  is  far  too  short  to  per- 
mit of  movements  of  the  ocular  muscles,  that  such  movements 
are  not  essential.  The  truth  seems  to  lie  midway ;  for  while 
simple  figures  may  not  require  them,  the  more  complex  do,  or, 
at  all  events,  the  judgment  is  very  greatly  assisted  thereby.  It 
is  of  the  utmost  importance  to  bear  in  mind  that  all  visual 
judgments  are  the  result  of  many  processes,  in  which,  not  the 
sense  of  vision  alone,  but  others,  are  concerned ;  and  the  mutual 
dependence  of  one  sense  on  another  is  great,  probably  beyond 
our  powers  to  estimate.  Reference  has  been  made  to  this  sub- 
ject previously. 


Protective  Mechanisms  of  the  Eye. 

The  eyelids  have  been  appropriately  compared  to  the  shut- 
ters of  a  window.  They  are,  however,  not  impervious  to  light, 
as  any  one  may  convince  himself  by  noticing  that  he  can  locate 
the  position  of  a  bright  light  with  the  eyes  shut ;  also  that  a 
sensitive  person  (child)  will  turn  away  (reflexly)  from  a  light 
when  sleeping  if  it  be  suddenly  brought  near  the  head.  The 
Meibomian  glands,  a  modification  of  the  sebaceous,  secrete  an 
oily  substance  that  seems  to  protect  the  lids  against  the  lachry- 


VISION. 


597 


mal  fluid,  and  prevents  the  latter  running  over  their  edges  as 
oil  would  on  the  margins  of  a  vessel.  The  lachrymal  gland  is 
not  in  structure  unlike  the  parotid,  the  secretion  of  which  its 
own  somewhat  resembles. 

The  saltness  of  the  tears,  owing  to  abundance  of  sodium 
chloride,  is  well  known  to  all.  The  nervous  mechanism  of  se- 
cretion of  tears  is  usually  reflex,  the  stimulus  coming  from  the 
action  of  the  air  against  the  eyeball  or  from  partial  desiccation 
owing  to  evaporation.  When  the  eyeball  itself,  or  the  nose,  is 
irritated,  the  afferent  nerves  are  the  branches  of  the  fifth,  to 
which  also  belong  the  efferent  nerves.  The  latter  include  also 
the  cervical  sympathetic.  But  it  will,  of  course,  be  understood 
that  the  afferent  impulses  may  be  derived  through  a  large  num- 
ber of  nerves,  and  that  the  secreting  cen- 
ter may  be  acted  upon  directly  by  the 
cerebrum  (emotions).  The  excess  of  lach- 
rjTnal  secretion  is  carried  away  by  the 
nasal  duct  into  which  the  lachrymal 
canals  empty.  While  it  is  well  known 
that  closure  of  the  lids  by  the  orbicularis 
muscle  favors  the  removal  of  the  fluid, 
the  method  by  which  the  latter  is  ac- 
complished is  not  agreed  upon.  Some 
believe  that  the  closure  of  the  lids  forces 
the  fluid  on  through  the  tubes,  when 
they  suck  in  a  fresh  quantity  ;  others  that 
the  orbicularis  drives  the  fluid  directly 
through  the  tubes,  kept  open  by  muscu- 
lar arrangements ;  and  there  are  several 
other  divergent  opinions.  The  prevention  of  winking  leads  to 
irritation  of  the  eye,  which  may  assume  a  serious  character,  so 
that  the  obvious  use  of  the  secretion  of  tears  is  to  keep  the  eye 
both  moist  and  clean. 


Fig, 


Lachiymal  canals, 
lachrymal  sac,  and  nasal 
canal,  opened  from  the 
front  (after  Sappey). 


Special  Considerations. 


Comparative. — It  seems  to  be  established  that  certain  animals 
devoid  of  eyes,  as  certain  myriopods,  are  able  to  perceive  the 
presence  of  light,  even  wlien  the  heat-rays  are  cut  off.  The  most 
ruflimentary  beginning  of  a  visual  apparatus  appears  to  be  a 
mass  of  pigment  with  a  nerve  attached,  as  in  certain  worms; 
though  it  is  questionable  whether  mere  collections  of  pigment 
witliout  nerves  may  not  in  some  instances  represent  still  earlier 


598 


ANIMAL   PHYSIOLOGY. 


mdiments  of  our  eyes.  Among  invertebrates,  eyes  may  in  gen- 
eral be  divided  into  two  classes :  1.  The  compound  or  faceted 
eyes,  the  structure  of  wbicli  may  be  gathered  from  the  accom- 
panying figures.  It  will  be  noted  that  in  such  the  retina  is  con- 
vex, and  is  made  up  of  large  compound  nerve-rods  {retinulce), 
separated  from  one  another  by  pigment-sheaths.    The  picture 


Fig.  439. 


Fig.  440. 

Fig.  439.— Diagrammatic  representation  of  compound  eye  in  an  Arthropod  (after  Glaus).  C, 
cornea ;  K,  crystalline  lens  ;  P,  pigment ;  R,  nerve-rods  of  retina  ;  ^"6,  layer  of  fibers ; 
(tz,  layer  of  ganglion  cells  ;  Rf,  retinal  fibers  ;  Fk^  crossing  of  fibers. 

Fig.  440.— Three  facets  with  retinulse  from  compound  eye  of  cockchafer  (after  Grenacher). 
Pigment  has  been  dissolved  away  from  two  of  the  facets.  F.  corneal  facet ;  K,  crystalline 
cone ;  P,  pigment- sheath ;  P',  chief  pigment-cell ;  P",  pigment-cells  of  second  order ; 
R,  retinal^. 

formed  by  such  eyes  must  represent  a  sort  of  mosaic,  and  be 
rather  deficient  in  definition  and  brightness.  It  will  be  noticed 
that  in  such  eyes,  both  the  cornea  and  crystalline  lens  of  verte- 
brates are  represented  in  multiple  form.  This  form  of  eye  is 
found  in  crustaceans  and  some  insects.  2.  The  simple  eye  pre- 
vails among  annelids,  insects,  arachnids,  mollusks,  and  verte- 
brates. A  more  advanced  form  of  such  a  visual  organ  is  found 
in  the  cuttle-fish.  It  may  be  seen  (Fig.  442)  that  such  an  eye 
corresponds  fairly  well  with  the  eye  of  a  vertebrate. 

The  eye  of  the  fish  is  characterized  by  flatness  of  the  cornea ; 


A 


VISION. 


599 


spherical  form  of  the  lens,  the  anterior  surface  of  which  pro- 
jects far  beyond  the  pupillary  opening ;  the  presence  of  a  pro- 


FiG.  441. — Transverse  section  of  the  simple  eye  of  a  beetle  larva  (after  Glaus  and  Grenadier). 
CL,  corneal  lens;  Gfc,  subjacent  hypodermic  cells  (vitreous  humor);  P,  pigment  in  periph- 
eral cells  of  latter  ;  Rz,  retinal  cells  ;  St,  cuticular  rods  of  latter. 

cess  of  the  choroid  ( processus  falciformis) ;  and  usually  the 
absence  of  eyelids,  the  cornea  being  covered  with  transparent 
skin. 

The  eye  of  the  bird,  in  some  respects  the  most  perfect  visual 


Kio. 412 


-Dia^rrammatic  horizontal  action  of  eye  of  cuttlf;  flsh  (ufUr  Flenscn  and  (iejrenbaur). 
■    -  --  ...     •.!         .....  .c  . —  .  /;/jntertial  lay«!r 


>.  n«  —  i^iaKrainmaT.ic  non/.dniai  tv'.cuoii  oi  eyt;  <ii  uim  n,  iinn  uii  i-<i  in-urn-n  ami  ...urii./u, 
KK,  rj-j,\in\U:  cariilai?<-H  ;  C,  cornea  ;  L.  Icnw  ;  rj,  ciliary  body  of  lens;  W/,  internal  la 
of  retina  ;  /{<:  <:xu-niii\  layer  of  retina  :  7-',  pigment  layer  ;  o,  optic  nerve  ;  yo,  gaugli 


k,  papillary  cartilage  ;  ik,  cartilagi?  of  iriH 


600 


ANIMAL   PHYSIOLOGY. 


organ  known,  is  of  peculiar  shape  as  a  whole,  presenting  a  large 
posterior  surface  for  retinal  expansion ;  a  very  convex  cornea, 
a  highly  developed  lens,  an  extremely  movable  iris ;  eyelids 
and  a  nictitating  membrane  (third  eyelid),  which  may  be  made 
to  cover  the  whole  of  the  exposed  part  of  the  eye,  and  thus 
shield  screen-like  from  excess  of  light ;  ossifications  of  the  scle- 
rotic ;  a  structure  which  is  a  peculiar 
modification  of  the  choroid,  of  which  it 
is  a  sort  of  offshoot  and  like  it  very 
vascular,  answering  to  the  falciform 
process  of  the  eye  of  the  fish  and  the 
reptile.  From  its  appearance  it  is 
termed  the  pecten.  Birds,  on  account 
of  a  highly  developed  ciliary  muscle, 
possess  wonderful  powers  of  accommo- 
dation, rendered  important  on  account 
of  their  rapid  mode  of  progression. 
They  also  seem  to  be  able  to  alter  the 
size  of  the  pupil  at  will. 

Evolution. — From  the  above  brief  ac- 
count of  the  eye  in  different  grades  of 
animals,  it  will  appear  that  its  modifi- 
cations answer  to  differences  in  the 
environment. 

Adaptation  is  evident.  Darwin  believes  this  to  have  been 
effected  partly  by  natural  selection — i.  e.,  the  survival  of  the 
animal  in  which  the  form  of  eye  appeared  best  adapted  to  its 
needs,  and  partly  by  the  use  or  disuse  of  certain  parts. 

The  latter  is  illustrated — 1.  By  the  blind  fishes,  insects,  etc., 
of  certain  caves,  as  those  of  Kentucky ;  and  it  is  of  extreme  in- 
terest to  note  that  various  grades  of  transition  toward  complete 
blindness  are  observable,  according  to  the  degree  of  darkness  in 
which  the  animal  is  found  living,  whether  wholly  within  the 
cave  or  where  there  is  still  some  light.  A  crab  has  been  found 
with  the  eye-stalk  still  present,  but  the  eye  itself  atrophied. 
Again,  animals  that  burrow  seem  to  be  in  process  of  losing 
their  eyes,  through  inflammation  from  obvious  causes ;  and  some 
of  them,  as  the  moles,  have  the  eye  still  existing,  though  well- 
nigh  or  wholly  covered  with  skin.  Internal  parasites  are  often 
without  eyes.  It  is  not  difficult  to  understand  how  one  bird  of 
prey,  with  eyes  superior  to  those  of  its  fellows,  would  gain 
supremacy,  and,  in  periods  of  scarcity,  survive  and  leave  off- 
spring when  others  would  perish. 


Fig.  443.— Eye  of  nocturnal  bird 
of  prey  (after  Wiedersheim). 
Co,  cornea  ;  L,  lens  ;  Rt,  ret- 
ina ;  P.  pecten  ;  No,  optic 
nerve  ;  8c.  ossification  of  scle- 
rotic coat ;  CM,  ciliary  mus- 
cle. Birds  have  unusually 
keen  vision,  great  power  of 
accommodation,  and  extreme 
mobility  of  the  iris. 


VISION. 


601 


It  is,  of  course,  impossible  to  trace  each,  step  by  which  the 
vertebrate  eye  has  been  developed  from  more  rudimentary 
forms,  though  the  data  for  such  an  attempt  have  greatly 
accumulated  within  the  last  few  years ;  and  it  is  not  to  be  for- 
gotten that  even  the  vertebrate  eye  has  many  imperfections, 
so  that  no  doctrine  of  complete  adaptation,  according  to  the 
argument  from  design  as  usually  understood,  can  apply. 

Certain  acquired  imperfections  of  the  eye  seem  to  be  multi- 
plying at  the  present  day,  such  as  myopia,  weakness  of  the 
accommodative  mechanism,  etc.  The  excessive  use  of  the  eyes, 
necessitating  undue  exercise  of  this  apparatus  or  strain  of  the 
accommodation,  is  the  fruitful  source  of  evil.  A  good  light — 
that  is,  one  both  sufficient  in  quantity  and  falling  in  the  right 
direction  upon  the  eyes  and  the  objects  to  be  viewed,  together 
with  adequate  ventilation  of  the  rooms  occupied — is  of  great 
importance,  though,  as  in  the  case  of  other  organs,  it  is  impos- 
sible to  avoid  wholly  the  penalties  of  over-use  of  the  visual 
apparatus. 

It  is  of  great  importance  to  recognize  that  what  we  really 
see  depends  more  upon  the  brain  and  the  mind  than  the  eye. 
If  any  one  will  observe  how  frequent  are  his  incipient  errors 


Brain  above 
medulla 


Centre  in  region  of- 
corp.  quadrigemina 


r- -Cortical  centre 


-Centre  in  optic  thalamus  . 


Retina 


Fio.  ^♦4.~r)iatn'am  inU^ndud  to  illijHtrate  the  elaboration  of  viKiial  impulses,  bepinniiiff  in 
retina  aii'l  eiilniinatint^  in  the  cerebral  cortex.  Omrse  of  impulses  is  indic'ited  \,y  arrows. 
Kn'>wle(|;.'e  rif  jiiKlitory  centJTH  JH  not  yet  c^xaet  erionijh  to  permit,  of  the  coiisl  riielion  of  a 
■  liatcram.  ilionch  rloiihtless  eventuall.y  the  central  processes  will  he  locali/.ed  as  with  vision. 
The  latter  remark  applies  Ui  the  other  HenseH  U)  nearly  the  uame  extent,  possibly  quite  Wi 
much. 


602  ANIMAL  PHYSIOLOGY. 

of  vision  speedily  corrected,  he  will  realize  the  truth  of  the 
above  remark.  Precisely  the  same  data  furnished  by  the  eye 
are  in  one  mind  worked  up  in  virtue  of  past  experience  (educa- 
tion) into  an  elaborate  conception,  while  to  another  they  an- 
swer only  to  certain  vague  forms  and  colors.  And  herein  lies 
the  great  superiority  of  man's  vision  over  that  of  all  other 
animals. 

Within  the  limits  of  their  mental  vision  do  all  creatures  see. 
Man  has  not  the  keen  ocular  discriminating  power  of  the  hawk ; 
he  can  neither  see  so  far  nor  so  clearly ;  nor  has  he  the  wide 
field  of  vision  of  the  gazelle ;  but  he  has  the  mental  resource 
which  enables  him  to  make  more  out  of  the  materials  with 
which  his  eyes  furnish  him.  It  is  by  virtue  of  his  higher  cere- 
bral development  that  he  has  added  to  his  natural  eyes  others 
in  the  microscope  and  telescope,  which  none  of  Nature's  forms 
can  approach. 

Pathological. — There  may  be  ulceration  of  the  cornea,  inflam- 
mation of  this  part,  or  various  other  disorders  which  lead  to 
opacity.  The  low  vitality  of  this  region,  probably  owing  to 
absence  of  blood-vessels,  is  evidenced  by  the  slowness  with 
which  small  ulcers  heal.  Opacity  of  the  lens  (cataract)  when 
complete  causes  blindness,  which  can  be  only  partially  reme- 
died by  removal  of  the  former.  Inflammations  of  any  part  of 
the  eye  are  serious,  from  possible  adhesions,  opacities,  etc.,  fol- 
lowing. Should  such  be  accompanied  by  great  excess  of  intra- 
ocular tension,  serious  damage  to  the  retina  may  result.  Of 
course,  atrophy  of  the  optic  nerve  (due  to  lesions  in  the  brain, 
etc.)  is  irremediable,  and  involves  blindness.  Inspection  of  the 
internal  parts  of  the  eye  (fundus  oculi)  often  reveals  the  first 
evidence  of  disease  in  remote  parts,  as  the  kidneys. 

From  what  has  been  said  of  the  movements  of  the  two  eyes 
in  harmony,  etc.,  the  student  might  be  led  to  infer  that  disease 
of  one  organ,  in  consequence  of  an  evident  close  connection  of 
the  nervous  mechanism  of  the  eyes,  would  be  likely  to  set  up 
a  corresponding  condition  in  the  other  unless  speedily  checked. 
Such  is  the  case,  and  is  at  once  instructive  and  of  great  prac- 
tical moment. 

Paralysis  of  the  various  ocular  muscles  leads  to  squinting, 
as  already  noticed. 

Brief  Synopsis  of  the  Physiology  of  Vision. — All  the  other  parts 
of  the  eye  may  be  said  to  exist  for  the  retina,  since  all  are  re- 
lated to  the  formation  of  a  distinct  image  on  this  nervous  ex- 
pansion.    The  principal  refractive  body  is  the  crystalline  lens. 


VISION.  603 

The  iris  serves  to  regulate  the  quantity  of  light  admitted  to 
the  eye,  and  to  cut  o&  too  divergent  rays.  In  order  that  objects 
at  different  distances  may  be  seen  distinctly,  the  lens  alters  in 
shape  in  response  to  the  actions  of  the  ciliary  muscle  on  the 
suspensory  ligament,  the  anterior  surface  becoming  more  con- 
vex. Accommodation  is  associated  with  convergence  of  the 
visual  axes  and  contraction  of  the  pupil.  The  latter  has  circu- 
lar and  radiating  plain  muscular  fibers  (striped  in  birds,  that 
seem  to  be  able  to  alter  the  size  of  the  pupil  at  will),  governed 
by  the  third,  fifth,  and  sympathetic  nerves.  Contraction  of 
the  pupil  is  a  reflex  act,  the  nervous  center  lying  in  the  front 
part  of  the  floor  of  the  aqueduct  of  Sylvius,  while  the  action 
of  the  other  center  (near  this  one)  through  the  sympathetic 
nerve  is  tonic. 

Accommodation  through  the  ciliary  muscle  is  governed  by 
a  center  situated  in  the  hind  part  of  the  floor  of  the  third  ven- 
tricle near  the  anterior  bundles  of  the  third  nerve,  which  latter 
is  the  medium  of  the  change.  There  are  certain  imperfections 
common  to  all  human  eyes,  such  as  spherical  and  chromatic 
aberration,  a  limited  degree  of  astigmatism,  etc.  When  rays 
of  light  are  focused  anterior  to  the  retina,  the  eye  is  myopic ; 
when  posterior  to  it,  hypermetropic. 

The  presbyopic  eye  is  one  in  which  the  mechanism  of  accom- 
modation is  at  fault,  chiefly  the  ciliary  muscle.  The  point  of 
entrance  of  the  optic  nerve  (blind-spot)  is  insensible  to  light ; 
and  visual  impulses  can  be  shown  to  originate  in  the  layers  of 
rods  and  cones,  probably  through  stimulation  from  chemical 
changes  effected  by  light  acting  on  the  retina.  The  sensation 
outlasts  the  stimulus ;  hence  positive  after-images  occur.  Nega- 
tive after-images  occur  in  consequence  of  excessive  stimulation 
and  exhaustion  of  the  retina,  or  disorder  of  the  chemical  pro- 
cesses that  excite  visual  impulses.  When  stimuli  succeed  one 
another  with  a  certain  degree  of  rapidity,  sensation  is  continu- 
ous. The  eye  can  distinguish  degrees  of  light  within  certain 
limits,  varying  by  about  -j-W  oi  the  total. 

Objects  become  fused  or  are  seen  as  one  when  the  rays  from 
them  falling  on  tlie  retina  approximate  too  closely  on  that  sur- 
face. The  brain,  as  well  as  the  eye  itself,  is  concerned  in  such 
discriminations,  the  former  probably  more  than  the  latter.  The 
various  color  sensations  wo  have  are  the  nssult  either  of  definite 
single  sensations  or  the  fusion  physiologi(;ally  of  two  or  more 
of  the.se,  and  have  no  reference  to  the  fusion  of  pigments  ex- 
ternal to  the  eye.     All  human  eyes  are  to  some  extent  color- 


604  ANIMAL   PHYSIOLOGY. 

blind  in  the  sense  that  it  is  probable  that  other  animals  (ants, 
etc.)  can  perceive  colors  not  included  in  our  spectrum,  and  also 
in  the  sense  that  all  parts  of  the  retina  are  not  equally  sensitive 
to  rays  of  a  certain  wave-length ;  but  some  persons  are  unable 
to  perceive  certain  colors  at  all. 

The  macula  lutea,  and  especially  the  fovea  centralis,  are  the 
points  of  greatest  retinal  sensitiveness.  When  the  images  of 
objects  are  thrown  on  these  parts,  they  are  seen  with  complete 
distinctness ;  and  it  is  to  effect  this  result  that  the  movements 
of  the  two  eyes  in  concert  take  place.  An  object  is  seen  as  one 
when  the  position  of  the  eyes  (visual  axes)  is  such  that  the  im- 
ages formed  fall  on  corresponding  parts  of  the  retina.  Binocu- 
lar vision  is  important  to  supply  the  sensory  data  for  the  idea  of 
solidity.  It  is  important  to  remember  that,  before  an  object  is 
"  seen  "  at  all,  the  sensory  impressions  furnished  by  the  retina 
and  conveyed  inward  by  the  optic  nerve  are  elaborated  in  the 
brain  and  brought  under  the  cognizance  of  the  perceiving  ego. 
We  recognize  many  visual  illusions  and  imperfections  of  vari- 
ous kinds,  the  course  of  which  it  is  difficult  to  locate  in  any 
one  part  of  the  visual  tract,  such  as  are  referred  to  "  irradia- 
tion," "  contrast,"  etc.  There  may  also  be  visual  phenomena 
that  are  purely  subjective,  and  others  that  result  from  sugges- 
tion rather  than  any  definite  sensory  basis  of  retinal  images. 
Hence  what  one  sees  depends  on  his  state  of  mind  at  the  time. 

This  applies  to  appreciation  of  size  and  distance  also,  though 
in  such  cases  we  have  the  visual  angle,  certain  muscular  move- 
ments (muscular  sense),  the  strain  of  accommodation,  etc.,  as 
guides. 


HEARING. 

As  the  end-organ  of  vision  is  protected  both  without  and 
within,  so  is  the  still  more  complicated  end-organ  of  the  sense 
of  hearing  more  perfectly  guarded  against  injury,  being  in- 
closed within  a  membranous  as  well  as  bony  covering  and  sur- 
rounded by  fluid,  which  must  shield  it  from  stimulation,  except 
through  this  medium. 

Hearing  proper,  as  distinguished  from  the  mere  recognition 
of  jars  to  the  tissues,  can,  in  fact,  only  be  attained  through  the 
impulses  conveyed  to  the  auditory  brain-centers,  as  originated 
in  the  end-organ  by  the  vibrations  of  the  fluid  with  which  it  is 
bathed. 


M 


HEARING. 


605 


It  will  be  assumed  that  the  student  has  made  himself  famil- 
iar with  the  general  anatomy  of  the  ear.  The  essential  points 
in  regard  to  sound  are  considered  in  the  chapter  on  "  The 
Voice.'*  It  will  be  remembered  that  what  we  term  a  musical 
tone,  as  distinguished  from  a  noise,  is  characterized  by  the 
regularity  of  vibrations  of  the  air  that  reach  the  ear ;  and  that 
just  as  ethereal  vibrations  of  a  certain  wave-length  give  rise  to 
the  sensation  of  a  particular  color,  so  do  aerial  vibrations  of  a 
definite  wave-length  originate  a  certain  tone.  In  each  case  must 
we  take  into  account  a  physical  cause  for  the  physiological 
effect,  and  these  bear  a  very  exact  relationship  to  one  another. 

As  will  be  seen  later,  while  in  all  animals  that  have  a  well- 
defined  sense  of  hearing  the  process  is  essentially  such  as  we 
have  indicated  above,  the  means  leading  up  to  the  final  stimu- 
lation of  the  end-organ  are  very  various.  At  present  we  shall 
consider  the  acoustic  mechanism  in  mammals,  with  special  ref- 
erence to  man.     There  are  in  fact  three  sets  of  apparatus :  (1) 


Fio.  445.— S«'ction  throiij?h  ariflit/>ry  or^an  (after  Sappey).  1.  pinna  ;  2.  4.  5,  cavity  of  concha, 
external  and  auditory  iru-atiis  with  oi)eninK  of  (•cruininous  glands ;  G,  nienibrana  tynipani ; 
7,  anterior  part  of  incus  ;  K,  malleuK  ;  9,  lonfj  handle  of  in.-illiMis,  Mllached  to  internal  sur- 
fa<;e  of  tympanic  memV)rane— it  is  here  represented  as  stnuifrly  imlravvn  ;  10.  tensor  tym- 
pani  riiusele  ;  II.  tympanic  cavity;  12,  Kiistaehian  tube  ;  l.S,  suiierior  semicircidar  canal  ; 
14.  nosterior  semicircular  canal  ;  l.").  external  semicircular  canal  :  KJ,  cochlea  ;  17,  internal 
anrfitory  meatus  :  IH,  facial  nerve  ;  1!),  larfje  petrosal  nerve  ;  at),  vestibular  branch  of 
auditory  nerve  ;  iJl,  cochlear  branch  of  same. 

otk;  foi'  collecting  the  aerial  vibrations;  (2)  one  for  transmit- 
ting th(;Tn  ;  and  (3)  one  for  receiving  the  impression  through  a 
fluid  truidiimi  ;  in  otlnT  words,  an  external,  middle,  and  internal 
ear. 


606 


ANIMAL   PHYSIOLOGY. 


The  external  ear  in  man  being  practically  immoYable,  owing 
to  the  feeble  development  of  its  muscles,  has,  as  compared  with 
such  animals  as  the  horse  or  cow,  but  little  use  as  a  collecting 
organ  for  the  vibrations  of  the  air.  The  meatus  or  auditory 
canal  may  be  regarded  both  as  a  conductor  of  vibrations  and 
as  protective  to  the  middle  ear,  especially  the  delicate  drum- 
head, since  it  is  provided  with  hairs  externally  in  particular, 
and  with  glands  that  secrete  a  bitter  substance  of  an  unctuous 
nature. 

The  Membrana  Tympani  is  concavo-convex  in  form,  and,  hav- 
ing attached  to  it  the  chain  of  bones  shortly  to  be  noticed,  is 
well  adapted  to  take  up  the  vibrations  communicated  to  it  from 
the  air  ;  though  it  also  enters  into  sympathetic  vibration  when 


Fig.  446.— Photographic  representation  of  right  membrana  tympani,  viewed  from  within 
(after  Flint  and  Rudinger).  1,  divided  head  of  malleus  ;  2.  neck  ;  3,  handle,  with  attach- 
ment of  tendon  of  tensor  tympani ;  4,  divided  tendon  ;  5,  6,  long  handle  of  malleus ;  7, 
outer  radiating  and  inner  circular  fibers  of  tympanic  membrane ;  8,  fibrous  ring  encircling 
membrana  tympani ;  9,  14,  15,  dentated  fibers  of  Gruber  ;  10,  11,  posterior  pocket  connect- 
ing with  malleus  ;  12,  anterior  pocket ;  13,  chorda  tympani  nerve. 


the  bones  of  the  head  are  the  medium,  as  when  a  tuning-fork 
is  held  between  the  teeth.      Ordinary  stretched  membranes 


HEARING. 


60T 


have  a  fundamental  (self -tone,  proper  tone)  tone  of  their  own, 
to  which  they  respond  more  readily  than  to  others. 

If  such  held  for  the  membrana  tympani,  it  is  evident  that 
certain  tones  would  be  heard  better  than  others,  and  that  when 
the  fundamental  one  was  produced  the  result  might  be  a  sen- 
sation unpleasant  from  its  intensity.  This  is  partially  obviated 
by  the  damping  effect  of  the  auditory  ossicles,  which  also  pre- 
vent after-vibrations. 

Some  suppose  that  what  we  denominate  shrill  or  harsh 
sounds  are,  in  part  at  least,  owing  to  the  auditory  meatus  hav- 
ing a  corresponding  fundamental  note  of  its  own. 

The  Auditory  Ossicles. — Though  these  small  bones  are  con- 
nected by  perfect  joints,  permitting  a  certain  amount  of  play 
upon  one  another,  experiment  has  shown  that  they  vibrate  in 
response  to  the  movements  of  the  drum-head  en  masse  j  though 


Kio.  iVl 


.  . t(  — SiK-tion  of  auditory  organ  of  honw-  faft»!r  Thauveau).  A,  muWUtry  canal  •  /?  mem- 
brana tymrmni  :  C,  inallfUH  ;  I),  inc-iiK  ;  /-',  HtafXH  ;  Oy  manUM  coIIh  ;  //,  fenestra  ovalis  • 
/,  vi-Htibule  ;  ./.  K,  L,  outline  of  Hemicircular  canala ;  M,  coclilea ;  A^,  commencemeut  of 
Hcalu  tyiiipaui. 


608 


ANIMAL   PHYSIOLOGY. 


the  stapes  has  by  no  means  the  range  of  movement  of  the  han- 
dle of  the  malleus ;  in  other  words,  there  is  loss  in  amplitude, 
but  gain  in  intensity.  A  glance  at  Fig.  448  will  show  that  the 
end  attained  by  this  arrangement  of  membrane  and  bony  levers, 
which  may  be  virtually  reduced  to  one  (as  it  is  in  the  frog,  etc.), 
is  the  transmission  of  the  vibrations  to  the  membrane  of  the 
fenestra  ovalis,  through  the  stapes  finally,  and  so  to  the  fluids 
within  the  internal  ear.    But  it  might  be  supposed  that,  for  the 


Fig.  448.— Diagrammatic  representation  illustrating  auditory  processes  (after  Beaunis).  A, 
external  ear  ;  B,  middle  ear  ;  C,  internal  ear  ;  1,  auricle  ;  2,  external  auditory  meatus  ;  3, 
tympanum  ;  4,  membrana  tympani ;  5,  Eustachian  tube  ;  6,  mastoid  cells  ;  10,  foramen 
rotundum  ;  11,  foramen  ovale  ;  12,,  vestibule  ;  13,  cochlea  ;  14,  scala  tympani ;  15,  scala 
vestibuli ;  16,  semicircular  canals. 

N.  B. — The  ear  is  so  complicated  an  organ  that  it  is  almost  impossible  to  give  a  diagram- 
matic representation  of  it  at  once  simple  and  complete  in  a  single  figure.  A  comparison 
of  the  whole  series  of  cuts  is  therefore  desirable.  It  is  essential  to  understand  how  the 
end-organ  within  the  scala  media  is  stimulated. 

avoidance  of  shocks  and  the  better  adaptation  of  the  apparatus 
to  its  work,  some  regulative  apparatus,  in  the  form  of  a  nerv- 
ous and  muscular  mechanism,  would  have  been  evolved  in  the 
higher  groups  of  animals.  Such  is  found  in  the  tensor  tym- 
pani, laxator  tympani,  and  stapedius  muscles,  as  well  as  the 
Eustachian  tube. 

Muscles  of  the  Middle  Ear. — The  tensor  tympani  regulates  the 
degree  of  tension  of  the  drum-head,  and  hence  its  amplitude  of 
vibration,  having  a  damping  effect,  and  thus  preventing  the  ill 
results  of  very  loud  sounds. 

Ordinarily  this  is,  doubtless,  a  reflex  act,  in  which  the  fifth 


HEARING.  609 

is  usually  the  afferent  nerve  concerned.  It  is  well-known  that, 
when  we  are  aware  that  an  explosion  is  about  to  take  place,  we 
are  not  as  much  affected  by  it,  which  would  seem  to  argue  a 
voluntary  power  of  accommodation  ;  but  of  this  we  must  speak 
with  caution. 

According  to  some  authorities  the  laxator  tympani  is  not  a 
muscle,  but  a  supporting  ligament  for  the  malleus.  The  stape- 
dius, however,  has  the  important  function  of  regulating  the 
movements  of  the  stapes,  so  that  it  shall  not  be  too  violently 
driven  against  the  membrane   covering  the   fenestra   ovalis. 

The  two  muscles,  stapedius  and  tensor,  suggest  the  accom- 
modative mechanism  of  the  iris.  The  motor  nerve  of  the  sta- 
pedius is  derived  from  the  facial ;  of  the  tensor,  from  the  tri- 
geminus through  the  otic  ganglion. 

The  Eustachian  Tube. — Manifestly,  if  the  middle  ear  were 
closed  permanently,  its  air  would  gradually  be  absorbed.  The 
drum-head  would  be  thrust  in  by  outward  pressure,  and  become 
useless  for  its  vibrating  function.  The  Eustachian  tube,  by 
communicating  with  the  throat,  keeps  the  external  and  internal 
pressure  of  the  middle  ear  balanced.  Whether  this  canal  is 
permanently  open,  or  only  during  swallowing,  is  as  yet  unde- 
termined. 

One  may  satisfy  himself  that  the  middle  ear  and  pharynx 
communicate,  by  closing  the  nostrils  and  then  distending  the 
upper  air-passages  by  a  forced  expiratory  effort,  when  a  sense 
of  distention  within  the  ears  is  experienced,  owing  to  the  rise 
of  atmospheric  pressure  in  the  tympanum. 

Pathological. — Inflammation  of  the  tympanum  may  result  in 
a<lhesions  of  the  small  bones  to  other  parts  or  to  each  other,  or 
to  occlusion  of  the  Eustachian  tube  from  excess  of  secretion, 
cicatrices,  etc.,  in  consequence  of  which  the  relations  of  atmos- 
pheric pressure  become  altered,  the  membrani  tympani  being 
indrawn,  and  the  whole  series  of  conditions  on  which  the  nor- 
mal transmission  of  vibrations  depends  disturbed,  with  the 
natural  result,  partial  deafness.  The  hardness  of  hearing  ex- 
perienced during  a  severe  cold  in  the  head  (catarrh,  etc.)  is 
owing  in  great  part  to  the  occlusion  of  the  Eustachian  tube, 
which  may  be  either  partial  or  complete. 

By  filling  one  or  both  of  the  ears  external  to  the  mem- 
brana  tympani  with  cotton-wool,  one  may  satisfy  himself  how 
essential  for  hearing  is  the  vibratory  mechanism,  whicli  is,  of 
course,  under  sucli  circum.stances  inactive  or  nearly  so;  hence 
the  deafness. 

89 


610 


ANIMAL  PHYSIOLOGY. 


When  the  middle  ear  is  not  functionally  active,  it  is  still 
possible,  so  long  as  the  auditory  nerve  is  normal,  to  hear 
vibrations  of  a  body  (as  a  tuning-fork)  held  against  the  head ; 
though,  as  would  be  expected,  discrimination  as  to  pitch  is 
very  imperfect. 

Auditory  impulses  originate  within  the  inner  ear — that  is 
to  say,  in  the  vestibule  and  possibly  the  semicircular  canals. 


•^^li*^ 


Fig.  449.— Diagram  intended  to  illustrate  the  processes  of  hearing  (after  Landois").  AG, 
external  auditory  meatus ;  T,  tympanic  membrane  ;  K,  malleus  ;  a,  incus  ;  P,  middle 
ear  :  o,  fenestra  ovaUs :  r,  fenestra  rotunda ;  pi,  scala  tympani ;  vt,  scala  vestibuli ;  F, 
vestibule ;  S,  saccule  ;  U,  utricle  ;  H,  semicircular  canals  ;  TE,  Eustachian  tube.  Long 
arrow  indicates  line  of  traction  of  tensor  tympani ;  shprt  curved  one  that  of  Stapedius. 

but  especially  in  the  cochlea.  It  is  to  be  remembered  that  the 
whole  of  the  end-organ  concerned  in  hearing  is  bathed  by  endo- 
lymph ;  and  that  the  vibrations  of  the  latter  are  originated  by 


Fig.  450.— Section  through  one  of  the  coils  of  cochlea  (after  Chauveau).  ST,  scala  tympani ; 
SV,  ^cala  vestibuli ;  CC,  cochlear  canal  (scala  media);  Co,  organ  of  Corti ;  R,  membrane 
of  Reissner ;  b,  membrana  basilaris ;  Iso,  lamina  spiralis  ossea  ;  I,  membrana  tectoria ; 
1,  3,  rods  of  Corti ;  nc,  cochlear  nerve  with  its  ganglion,  gs. 


HEARING. 


611 


corresponding  vibrations  of  the  perilynipli,  which  again  is  sent 
into  oscillation  by  the  movements  of  the  stapes  against  the 
membrane  covering  the  fenestra  ovalis ;  so  that  the  vibrations 
thus  set  up  without  the  membranous  labyrinth  are  trans- 
formed into  similar  ones  within  the  vestibule  and  the  scala 
vestibuli,  and  end,  after  passing  over  the  scala  tympani,  against 
the  membrane  of  the  fenestra  rotunda.  The  cochlear  canal 
may  be  regarded  as  the  seat  of  the  most  important  part  of  the 
organ  of  hearing,  and  answers  to  the  macula  lutea  of  the  eye 
in  many  respects. 


Fio.  451.— I.  Transverse  section  of  a  turn  of  cochlea.  11.  Ampulla  of  a  semicircular  canal 
and  its  crista  acoustica  ;  apy  auditory  cells,  one  of  which  is  a  hair-cell.  HI.  Diagram  of 
labyrinth  of  man.    IV.  Of  bird.    V.  Of  fish.    (After  Landois.) 


The  organ  of  Corti  has  given  rise  to  certain  speculations 
which  require  a  brief  notice.  It  has  been  supposed  that,  as  the 
key-board  of  a  piano  may  be  said  to  cause  certain  tones  by 
being  associated  with  stretched  wires  of  varying  lengths,  so 
the  vibrations  of  the  rods  of  Corti  originate  in  certain  nerve- 
fibers  the  sensations  answering  to  the  different  tones  we  hear. 
It  was  found,  however,  (1)  that  these  rods,  though  very  nu- 
merous (0,000  to  10,000),  are  insufficient  to  account  for  the 
actual  range  of  our  hearing ;  (2)  that  they  are  absent  in  certain 
classes  of  animals  that  discriminate  sounds  very  well,  as  birds; 
and  (;j)  that  the  nerve-fibers  do  not  terminate  in  these  rods  at 
all,  but  in  the  hair-cells  of  the  organ  of  Corti.  It  is  now  pro- 
j)Osed  that  the  basilar  membrane  (present  in  birds)  may,  like  a 
series  of  tense  strings  of  different  lengths,  be  the  required 
organ.     The  failure  of  certain  theories  of  vision  should  have 


612 


ANIMAL  PHYSIOLOGY. 


made  physiologists  cautious  in  adopting  so  meclianical  an  expla- 
nation.    If  all  our  perceptions  of  color,  however  minute  the 


Fig.  452.— Diagrammatic  representation  of  ductus  cochlearis  and  organs  of  Corti  (after  Lan- 
dois).  N,  nerve  of  cochlea  ;  K,  inner,  and  P,  outer,  hair-cells ;  n,  nerve-fibrils  termi- 
nating in  P ;  a,  a,  supporting  cells  ;  d,  cells  of  succus  spiralis  ;  z,  inner  rod  of  Corti ;  y, 
outer  rod  of  Corti ;  nib,  membrane  of  Corti  (membrana  tectoria) ;  o,  membrana  reticu- 
laris ;  H,  G,  cells  of  area  toward  outer  wall. 

shade  of  difference  from  others  (and  some  believe  we  can  recog- 
nize millions  of  such  gradations),  are  the  result  of  the  fusion. 


A.N. 


P.S.C. 


Coch. 


Fig.  454. 


Fig.  453. 


Fig.  453.— Auditory  epithelium  from  macula  acoustica  of  saccule  of  alligator,  much  magni- 
fied (after  Schafer).  c,  c,  columnar  hair-cells  ;  /,  /,  fiber-cells  ;  n,  nerve-fiber  losing  its 
medullary  sheath  and  about  to  terminate  in  columnar  auditory  cells  :  h,  auditory  hair ; 
h',  base  of  auditory  hairs  split  up  into  fibrils. 

Fig.  454.— Diagrammatic  representation  of  distribution  of  auditory  nerve  in  membranous 
labyrinth  and  cochlea  (after  Huxley). 


HEARING. 


613 


etc.,  of  three  different  fuudamental  sensations,  or  the  result  of 
chemical  processes  few  in  kind,  why  should  not  hearing  be 
explained  in  an  eqiially  simple  way  ?     Such  views  as  those  re- 


a.h. H 


a.h 


A  B 

Fig.  455.— Lon^tudinal  section  of  ampulla,  somewhat  diagrammatic  (after  Huxley),  c.  end 
of  ampulla  joiniiitc  semicirciilar  canal  :  u,  opening  into  utricle  ;  cr,  crista  acoustica  with 
hair-cell.s,  to  whir'h  may  tx'  seen  pa-ssing,  n,  fibers  of  auditory  nerve  ;  ct,  connective-tissue 
support  for  aufiitory  hairs. 

ferred  to  above  seem  to  us  utterly  at  variance  with  the  funda- 
mental conceptions  of  biology ;  are  so  purely  conceptions  that 
have  their  birth  in  physics,  that  we  deem  it  wiser  to  rest  with- 
out any  attempt  at  an  explanation  of  the  origin  of  auditory 
sensations  in  detail,  than  to  accept  such  artificial  and  inadequate 
solutions  as  have  been  proposed.  Siihjerfive  sensations  of  hear- 
ing are  common  enough  in  the  insane,  and  answer  to  the  visions 
of  the  same  class  of  persons ;  so  that  we  must  recognize  the 
posKibility  of  such  sensations  arising  without  the  usual  external 
stiniuhis. 


614 


ANIMAL   PHYSIOLOGY. 


Fig.  456.— Diagram  intended  to  Illustrate  relative  position  of  various  parts  of  ear  (after  Hux- 
ley). E.M,  external  auditory  meatus  ;  Ty.  M,  tympanic  membrane  ;  Ty,  tympanum  ;  Mull, 
malleus ;  Inc,  incus  ;  Stp,  stapes  ;  F.o,  fenestra  ovalis  ;  F.  r,  fenestra  rotunda ;  Eu,  Eustachi- 
an tube ;  M.  L,  membranous  labyrinth,  only  one  of  the  semicircular  canals  and  its  anipullabe- 
ing  represented ;  Sea.  V,  Sea.  T,  Sea.  M,  scalse  of  cochlea,  represented  as  straight  (uncoiled). 


Fig.  457.— Photographic  diagram  of  labyrinth  (after  Fhnt  and  Riidinger).  Upper  figure :  1, 
utricle  ;  2,  saccule  ;  3,  5,  membranous  cochlea  ;  4,  canalis  reuniens  ;  6,  semicircular  canals. 
Lower  figure  :  1,  utricle  ;  2,  saccule  ;  3,  4,  6,  ampullae  ;  5,  7,  8,  9,  semicircular  canals  ;  10, 
auditory  nerve  (partly  diagrammatic) ;  11,  12,  13,  14,  15,  distribution  of  branches  of  nerve 
to  vestibule  and  semicircular  canals. 


HEARING,  615 

The  structure  of  the  ampullae  of  the  semicircular  canals, 
and  other  parts  of  the  labyrinth  besides  those  sj)ecially  con- 
sidered, with  their  peculiar  hair-cells,  suggests  an  auditory 
function ;  but  what  that  may  be  is  as  yet  quite  undetermined. 


Fifi.  458.— Distribution  of  cochlear  nerve  in  spiral  lamina  of  antero-inferior  part  of  cochlea  of 
right  ear  (after  Sappey).  1,  trunk  of  cochlear  nerve;  2,  membranous  zone  of  spiral 
lamina  ;  3,  terminal  expansion  of  cochlear  nerve  exposed  throughout  by  removal  of  supe- 
rior plate  of  lamina  spiralis  ;  4,  orifice  of  communication  between  scala  tympani  and 
scala  vestibuli. 

It  has  been  thought  that  the  parts,  other  than  the  cochlea,  are 
concerned  with  the  appreciation  of  noise,  or  perhaps  the  in- 
tensity of  sounds ;  but  this  is  a  matter  of  pure  speculation. 

Auditory  Sensations,  Perceptions,  and  Judgments. 

We  have  thus  far  been  concerned  with  the  conduction  of 
the  aerial  vibrations  that  are  the  physical  cause  of  hearing; 
but  before  we  can  claim  to  have  "  heard  "  a  word  in  the  highest 
sense,  certain  processes,  some  of  them  physiological  and  some 
X>sychical,  take  place,  as  in  the  case  of  vision ;  hence  we  may 
speak  of  the  affection  of  the  end-organ  or  of  auditory  impulses, 
and  of  the  processes  by  which  these  become,  by  the  mediation 
of  the  brain,  auditory  sensations,  and  when  brought  under  the 
cognizance  of  the  mind  as  auditory  perceptions  and  judg- 
ments. 

Auditory  Judgments. — Such  are  much  more  frequently  erro- 
neous than  are  our  visual  judgments,  whether  the  direction  or 
the  distance  of  the  sound  be  considered.  As  in  the  case  of  the 
eye,  the  muscular  sense,  from  accommodation  of  the  vibratory 
mechanism,  may  assist  our  judgments,  being  aided  by  our 
stored   past  experiences   (memory)   according  to   the   law   of 


616  ANIMAL  PHYSIOLOGY. 

association.  Sounds  are,  however,  always  referred  to  the  world 
without  US.  The  animals  with  movable  ears  greatly  excel  man 
in  estimating  the  direction,  if  not  the  distance,  of  sounds. 
There  are  few  physiological  experiments  more  amusing  than 
those  performed  on  a  person  blindfolded,  when  attempting  to 
determine  either  the  distance  or  the  direction  of  a  sounding 
tuning-fork,  so  gross  are  the  errors  made. 

One  who  makes  such  observations  on  others  may  notice 
that  most  persons  move  the  ears  slightly  when  attempting  to 
make  the  necessary  discriminations,  which  of  itself  tends  to 
show  how  valuable  mobility  of  these  organs  must  be  to  those 
animals  that  have  it  highly  developed. 

Range  of  Auditory  Discrimination. — If  we  compare  the  range 
of  sense-perception  of  eye  and  ear,  we  find  that  the  latter  is  in 
this  respect  far  superior  to  the  former.  Assuming  that  the 
perception  of  red  is  owing  to  the  influence  of  rays  of  light  with 
four  hundred  and  fifty-six  billions  of  vibrations  per  second  and 
violet  at  the  opposite  end  of  the  spectrum  with  rays  of  six  hun- 
dred and  sixty-seven  billions,  it  will  be  seen  that  the  total  range 
does  not  correspond  with  even  one  octave ;  while  the  ear  can 
discriminate  between  tones  answering  on  the  one  hand  to  about 
forty  aerial  vibrations  per  second  and  on  the  other  to  thirty- 
eight  thousand  or  more,  though  this  latter  is  greater  in  the 
upward  direction  than  most  persons  can  appreciate.  Such  lim- 
its answer  to  at  least  ten  times  that  for  the  eye.  On  the  other 
hand,  a  sense-impression  on  the  organ  of  hearing  lasts  a  shorter 
time  by  far  than  in  the  case  of  the  eye,  so  that  fusion  of  audi- 
tory sense-impressions  is  less  readily  produced. 

Special  Considerations. 

Comparative. — Among  invertebrates  steps  of  progressive  de- 
velopment can  be  traced.  Thus,  in  certain  of  the  jelly-fishes  we 
find  an  auditory  vesicle  (Fig.  459)  inclosing  fluid  provided  with 
one  or  more  otoliths  or  calcareous  nodules  and  auditory  cells 
with  attached  cilia,  the  whole  making  up  an  end-organ  connected 
with  the  auditory  nerve.  A  not  very  dissimilar  arrangement 
of  parts  exists  in  certain  mollusks  (Fig.  460).  The  vesicle  may 
lie  on  a  ganglion  of  the  central  nervous  system.  On  the  other 
hand,  the  vesicle  may  lie  open  to  the  exterior,  as  in  decapod 
crustaceans;  and  the  otoliths  be  replaced  by  grains  of  sand 
from  without.  It  is  diflicult  to  decide  what  the  function  of 
otoliths  may  be  in  mammals ;  but  there  seems  to  be  little  reason 


HEARING. 


617 


to  doubt  that  they  communicate  vibrations  in  the  invertebrates. 
When  the  cephalopod  mollusks,  with  their  highly  developed 
nervous  system,  are  reached,  we  find  a 
membranous  and  cartilaginous  laby- 
rinth. 

Among  veiiehraies  the  different  parts 
of  the  mammalian  ear  are  found  in  all 
stages  of  development.  The  outer  ear 
may  be  wholly  wanting,  as  in  the  frog, 
or  it  may  exist  as  a  meatus  only,  as  in 
birds.  The  tympanic  cavity  is  wanting 
in  snakes.  Most  fishes  have  a  utricle 
and  three  semicircular  canals,  but  some 
have  only  one ;  and  the  lowest  of  this 
group  have  an  ear  not  greatly  removed 
from  the  invertebrate  type,  as  may  be 
seen  in  the  lamprey,  which  has  a  saccule 
with  auditory  hairs  and  otoliths,  in  com- 
munication with  two  semicircular  ca- 
nals. Most  of  the  amphibia  are  without 
a  membrana  tympani.  The  frog  has  (1) 
a  membrana  tympani  communicating  with  the  inner  ear  by  (2) 
a  bony  and  cartilaginous  lever  {columella  auris),  and  (3)  an 
inner  ear  consisting  of  three  semicircular  canals,  a  saccule  and 


Fig.  459.  —  Auditory  vesicle  of 
Geryonia  (Carmarina),  seen 
from  the  surface  (after  O. 
and  R.  Hertwig).  X  and  N', 
the  auditory  nerves  ;  Ot,  oto- 
hth  :  Hz,  auditory  cells;  Hh, 
auditory  cilia  (type  of  the 
auditory  organ  of  the  Tra- 
chymedusce). 


Fio.  WJ.  —  Auditf>ry  veHiclc  of  a  hetf^ropod  molliiHk  ( Pterotrachca)  (after  ClaiiH).  N,  auditory 
nerve  ;  Ot,  f>ti)lith  in  fluid  of  vesicle  ;  IVz,  ciliated  cells  on  inner  wall  of  vesicle  ;  Hz,  audi- 
tory cells  ;  Cz,  central  cells. 


QIS  ANIMAL   PHYSIOLOGY. 

utricle  containing  many  otoliths,  and  a  small  dilatation  of  tlie 
vestibule,  which  may  indicate  an  undeveloped  cochlea.     The 


Fig.  461. — Otoliths  from  various  animals  (after  Riidinger).      1,   from  goat;  2,  herring;  3, 
devil-flsh  ;  4,  mackerel ;  5,  flying-fish  ;  6,  pike  ;  7,  carp  ;  8,  ray  ;  9,  shark  ;  10,  grouse. 

membranous  labyrinth  is  contained  in  a  periotic  capsule,  partly 
bony  and  partly  cartilaginous,  which  is  supplied  with  per- 
ilymph. There  is  a  fenestra  ovalis,  but  not  a  fenestra  rotunda, 
though  the  latter  is  present  in  reptiles.  In  crocodiles  and 
birds  the  cochlea  is  tubular,  straight,  and  divided  into  a  scala 
tympani  and  a  scala  vestibuli.  The  columella  of  lower  forms 
still  persists.  In  birds  and  mammals  the  bone  back  of  the  ear 
is  hollowed  out  to  some  extent  and  communicates  with  the 
tympanum.  Except  among  the  very  lowest  mammals  {Echid- 
na), the  ear  is  such  as  has  been  described  in  detail  already. 

Evolution. — The  above  brief  description  of  the  auditory  organ 
in  different  groups  of  the  animal  kingdom  will  suffice  to  show 
that  there  has  been  a  progressive  development  or  increasing 
differentiation  of  structure,  while  the  facts  of  physiology  point 
to  a  corresponding  progress  in  function — in  other  words,  there 
has  been  an  evolution.  No  doubt  natural  selection  has  played 
a  great  part.  It  has  been  suggested  that  this  is  illustrated  by 
cats,  that  can  hear  the  high  tones  produced  by  mice,  which 
would  be  inaudible  to  most  mammals ;  and,  as  the  very  exist- 
ence of  such  animals  must  depend  on  their  detecting  their  prey, 
it  is  possible  to  understand  how  this  principle  has  operated  to 
determine  even  what  cats  shall  survive.    The  author  has  noticed 


HEARING. 


619 


that  terrier  dogs  also  have  a  very  acute  sense  of  hearing,  and 
they  also  kill  rats,  etc.  But,  unless  it  be  denied  that  the  im- 
j)rovement  from  use  and  the  reverse  can  be  inherited,  this  fac- 
tor must  also  be  taken  into  the  account. 

There  seem  to  be  great  differences  between  hearing  as  it 
exists  in  man  and  in  lower  forms.  Birds,  and  at  least  some 
horses,  possibly  some  cats  and  dogs,  like  music,  and  give  evi- 
dence of  the  possession  of  a  sense  of  rhythm,  as  evidenced  by 
the  conduct  of  the  steed  of  the  soldier.  On  the  other  hand, 
some  dogs  seem  to  greatly  dislike  music.     Certain  animals  that 


G.C. 

Fig.  462.— Transverse  section  through  head  of  fcetal  sheep,  in  region  of  hind-brain,  to  illus- 
trate development  of  ear  (after  Bottcher).  H.  B.  hind-brain  ;  N,  auditory  nerve  ;  V.  B, 
vertical  semicircular  canal ;  CC,  canal  of  cochlea  ;  R.  V,  recessus  vestibuli ;  G.  C,  auditory 
ganglion  ;  G',  terminal  portion  of  auditory  nerve. 

appear  to  be  devoid  of  true  hearing,  as  spiders,  are  neverthe- 
less sensitive  to  aerial  vibrations  ;  whether  by  some  special  un- 
discovered organ  or  through  the  general  cutaneous  or  other  kind 
of  sensibility  is  unknown.  It  also  seems  to  be  more  than  prob- 
able that  some  groups  of  insects  can  hear  sounds  quite  inaudible 
to  us,  though  by  what  organs  is  in  great  measure  unknown. 

The  so-called  musical  ear  differs  from  the  non-musical  in 
the  ability  to  discriminate  differences  in  j^itch  rather  than  in 
quality  ;  in  fact,  that  one  defective  in  the  former  power  may 
possess  the  latter  in  a  higli  degree  is  a  fact  that  has  been  some- 
what h»st  sight  of,  })oth  tlieoretically  and  practically.  It  does 
not  at  all  follow  tiiat  one  with  little  capacity  for  tune  may  not 


Q20  ANIMAL   PHYSIOLOGY. 

have  the  qnalifications  of  ear  requisite  to  make  a  first-rate  elo- 
cutionist. Following  custom,  we  have  spoken  as  though  cer- 
tain defects  and  their  opposites  depended  on  the  ear,  but  in 
reality  we  can  not,  in  the  case  of  man  at  all  events,  affirm  that 
such  is  the  case ;  indeed,  it  seems,  on  the  whole,  more  likely 
that  they  are  cerebral  or  mental.  Auditory  discriminations 
seem  to  be  equally  if  not  more  susceptible  of  improvement  by 
culture  than  visual  ones,  especially  in  the  case  of  the  young. 

A  "  good  ear  "  seems  to  dejDend  in  no  small  degree  on  mem- 
ory of  sounds,  though  the  latter  may  again  have  its  basis  in  the 
auditory  end-organs  or  in  the  cerebral  cortex,  as  concerned  in 
hearing.  The  necessity  for  the  close  connection  between  the 
co-ordinations  of  the  laryngeal  apparatus  in  singing  and  speak- 
ing and  the  ear  might  be  inferred  from  the  fact  that  many  ex- 
cellent musicians  are  themselves  unable  to  vocalize  the  music 
they  perfectly  appreciate. 

Synopsis  of  the  Physiology  of  Hearing. — The  ear  can  appreciate 
differences  in  pitch,  loudness,  and  quality  of  sounds,  though 
whether  different  parts  of  the  inner  ear  are  concerned  in  these 
discriminations  is  unknown.  Hearing  is  the  result  of  a  series 
of  processes,  having  their  physical  counterpart  in  aerial  vibra- 
tions, which  begin  in  the  end-organ  in  the  labyrinth  and  ter- 
minate in  the  cerebral  cortex.  We  recognize  conducting  ap- 
paratus which  is  membranous,  bony,  and  fluid.  The  auditory 
nerve  conveys  the  auditory  impulses  to  the  brain,  though  ex- 
actly what  terminal  cells  are  concerned  and  how  in  originating 
them  must  be  regarded  as  undetermined.  The  essential  part  of 
the  organ  of  hearing  is  bathed  by  endolymph,  and  the  princi- 
pal part  (in  mammals)  is  within  the  cochlear  canal.  Man's 
power  to  locate  sounds  is  very  imperfect.  The  auditory  brain 
center  (or  centers)  has  not  been  definitely  located.  Compara- 
tive anatomy  and  physiology  point  clearly  to  a  progressive 
development  of  the  sense  of  hearing. 


THE  SENSE  OF  SMELL. 

The  nose  internally  may  be  divided  into  a  respiratory  and 
an  olfactory  region.  The  latter,  which  corresponds,  of  course, 
with  the  distribution  of  the  olfactory  nerve,  embraces  the  upper 
and  part  of  the  middle  turbinated  bone  and  the  upper  part  of 
the  septum,  all  of  which  differ  in  microscopic  structure  from 
the  respiratory  region.     Among  the  ordinary  cylindrical  epi- 


THE  SENSE  OP  SMELL. 


621 


thelium  of  the  olfactory  region  are  found  peculiar  hair-cells 
highly  suggestive  of  those  of  the  labyrinth  of  the  ear,  and 


Fig.  463. 


-Parts  concerned  in  smell  (after  Hirschfeld).    1,  olfactory  ganglion  and  nerves  ;  2, 
branch  of  nasal  nerve,  distributed  over  the  turbinated  bones. 


which  are  to  be  regarded  as  the  end-organs  of  smell.  If  aro- 
matic bodies  be  held  before  the  nose,  and  respiration  suspended, 
they  will  not  be  recognized  as  such, 
and  it  is  well  known  that  sniffing 
greatly  assists  the  sense  of  smell. 
Again,  if  fluids,  such  as  eau  de  Co- 
logne, be  held  in  the  nose,  their  aroma 
is  not  detected ;  and  immediately  after 
water  has  been  kept  in  the  nostrils 
for  a  few  seconds,  it  may  be  noticed 
that  smell  is  greatly  blunted.  Such 
is  the  case  also  when  the  mucous 
membrane  is  much  swollen  from  a 
cold.  There  can  be  no  doubt  that  the 
presence  of  fluid  in  the  above  cases  is 
injurious  to  the  delicate  hair-cells, 
and  that  smell  is  dependent  upon  the 
excitation  of  these  cells  by  extremely 
minute  particles  emanating  from  aro- 
matic bodies. 

When  ammonia  is  held  }>cfore  the 
nose,  a  powerful  sensation  is  experi- 
enced;  but  this  is  not  smell  })roper,  but  an  affection  of  ordi- 
nary .sensation,  owing  to  stimulation  of  the  terminals  of  the 


Fig.  464.— End-organs  concerned  in 
smell  (after  Ki'illiker).  1,  from 
frog— fi,  epithelial  cell  of  the  ol- 
factory area  ;  />,  olfactory  cell. 
2,  small  branch  of  olfactory 
nerve  of  frog,  breaking  up  into 
a  lirush  of  varicose  fiiicrs.  3, 
olfactory  cell  of  sheep. 


622  ANIMAL  PHYSIOLOGY. 

fifth  nerve.  It  is  possible  that  the  auditory  nerve  may  also 
participate,  though  certainly  not  so  as  to  produce  a  pure  sen- 
sation of  smell. 

Like  the  other  sense-organs,  that  of  smell  is  readily  fa- 
tigued ;  and  perhaps  the  satisfaction  from  smelling  a  bouquet 
of  mixed  flowers  is  comparable  to  viewing  the  same,  one  scent 
after  another  being  perceived,  and  no  one  remaining  predomi- 
nant. 

Our  judgment  of  the  position  of  bodies  possessing  smell  is 
less  perfect  even  than  for  those  emitting  sounds ;  but  we  always 
project  our  sensations  into  the  outer  world,  never  referring  the 
object  to  the  nose  itself.  Subjective  sensations  of  smell  are 
rare  in  the  normal  subject,  though  common  enough  among  the 
diseased,  as  is  complete  or  partial  loss  of  smell.  It  has  been 
found  that  injury  to  the  fifth  nerve  interferes  with  smell,  which 
is  probably  due  to  trophic  changes  in  the  olfactory  region. 

Comparative. — The  investigation  of  the  senses  in  the  lower 
forms  of  life  is  extremely  difficult,  and  in  the  lowe^  presents 
almost  insurmountable  obstacles  to  the  physiologist,  because 
their  psychic  life  is  so  far  removed  from  our  own  in  terms  of 
which  we  must  interpret,  if  at  all. 

The  earliest  form  of  olfactory  organ  appears  to  be  a  depres- 
sion lined  with  special  cells  in  connection  with  a  nerve,  which, 
indeed,  suggests  the  embryonic  beginnings  of  the  olfactory 
organ  in  vertebrates,  as  an  involution  (pit)  on  the  epithelium  of 
the  head  region.  It  would  appear  that  we  must  believe  that  in 
some  of  the  lower  forms  of  invertebrates  the  senses  of  smell 
and  taste  are  blended,  or  possibly  that  a  perception  resulfs 
which  is  totally  diiferent  from  anything  known  to  us.  The 
close  relation  of  smell  and  taste,  even  in  man,  will  be  referred  to 
presently.  There  are,  perhaps,  greater  individual  differences  in 
sensitiveness  of  the  nasal  organ  among  mankind  than  of  any 
other  of  the  sense-organs.  Women  usually  have  a  much  keener 
perception  of  odors  than  men.  The  sense  of  smell  in  the  dog 
is  well  known  to  be  of  extraordinary  acuteness ;  but  there  are 
not  only  great  differences  among  the  various  breeds  of  dogs, 
but  among  individuals  of  the  same  breeds ;  and  this  sense  is 
being  constantly  improved  by  a  process  of  "  artificial  selection  " 
on  the  part  of  man,  owing  to  the  institution  of  field  trials  for 
setters  and  pointers,  the  best  dogs  for  hunting  (largely  deter- 
mined by  the  sense  of  smell)  being  used  to  breed  from,  to  the 
exclusion  of  the  inferior  in  great  part.  Our  own  power  to 
think  in  terms  of  smell  is  very  feeble,  and  in  this  respect  the 


THE  SENSE  OF  TASTE.  623 

dog  and  kindred  animals  probably  have  a  world  of  their  own 
to  no  small  extent.  Their  memory  of  smells  is  also  immeasur- 
ably better  than  our  own.  A  dog  has  been  known  to  detect  an 
old  hat,  the  property  of  his  master,  that  had  been  given  away 
two  years  before,  as  evidenced  by  his  recovering  it  from  a 
remote  place. 

The  importance  of  smell  as  a  guide  in  the  selection  of  food, 
in  detecting  the  presence  of  prey  or  of  enemies,  etc.,  is  very 
obvious.  By  culture  some  persons  have  learned  to  distinguish 
individuals  by  smell  alone,  like  the  dog,  though  to  a  less  degree. 


THE  SENSE  OF  TASTE. 

The  tongue  is  provided  with  peculiar  modifications  of  epi- 
thelial cells,  etc.,  known  as  papillae  and  taste-buds  which  may 
be  regarded  as  the  end-organs  of  the  glosso-pharyngeal  and 
lingual  nerves ;  though  that  these  all,  especially  the  taste-buds, 
are  concerned  with  taste  alone,  seems  more  than  doubtful.  In 
certain  animals  with  rough  tongues,  the  papillae,  certain  of 
them  at  least,  answer  to  the  hairs  of  a  brush  for  the  cleansing 
and  general  preservation  of  the  coat  of  the  animal  in  good  con- 
dition. We  may,  perhaps,  speak  of  certain  fundamental  taste- 
perceptions,  such  as  sweet,  bitter,  acid,  and  saline.  Certainly 
the  natural  power  of  gustatory  discrimination  is  considerable ; 
and,  as  in  the  case  of  tea-tasters,  capable  of  extraordinary  culti- 
vation. All  parts  of  the  tongue  are  not  equally  sensitive,  nor 
IS  taste-sensation  confined  entirely  to  the  tongue.  It  can  be 
shown  that  the  back  edges  and  tip  of  the  tongue,  the  soft  palate, 
the  anterior  pillars  of  the  fauces,  and  a  limited  portion  of  the 
back  part  of  the  hard  palate,  are  concerned  in  tasting.  Making 
allowances  for  individual  differences,  it  may  be  said  that  the 
back  of  the  tongue  appreciates  best  bitter  substances,  the  tip, 
sweet  ones,  and  the  edges  acids. 

If  any  substance  with  a  decided  taste  be  placed  upon  the 
tongue  when  wiped  quite  dry,  it  can  not  be  tasted  at  all,  show- 
ing that  solution  is  essential. 

If  a  x>ioce  of  aj)i>le,  another  of  potato,  and  a  third  of  onion, 
be  ph'ujed  upon  the  tongue  of  a  person  blindfolded,  and  with 
the  nostrils  closed,  he  will  not  be  able  to  distinguish  tliom, 
showing  that  the  senses  of  smell  and  of  taste  are  related ;  or, 
perhaps,  it  may  be  said  that  much  that  we  call  tasting  is  in 
largo  part  smelling.     When  the  electrodes  from  a  battery  are 


624 


ANIMAL  PHYSIOLOGY. 


placed  on  the  tongue,  a  sensation  of  taste  is  aroused,  described 
differently  by  different  persons  ;  also  when  the  tongue  is  quick- 


FiG.  465.— Papillae  of  tongue  (after  Sappey).    1,  circumvallate  papillae  ;  3.  fungiform  papillae  ; 
4,  filiform  papillae  ;  6,  glands  at  base  of  tongue  ;  7,  tonsils. 


ly  tapped,  showing  that,  though  taste  is  usually  the  result  of 
chemical  stimulation,  it  may  be  excited  by  such  as  are  electrical 
or  mechanical. 

But  it  is  not  to  be  forgotten  that  we  have  usually  no  pure 
gustatory  sensations,  but  that  these  are  necessarily  blended 
with  those  of  common  sensation,  temperature,  etc.,  and  that  our 
judgments  must,  in  the  nature  of  the  case,  be  based  upon  highly 
complex  data,  even  leaving  out  of  account  other  senses  such  as 
vision. 


THE   SENSE  OF   TASTE. 


625 


The  glosso-pharyngeal  is  the  principal  nerve  for  the  back  of 
the  tongue,  and  for  the  tip,  the  lingual ;  or  according  to  some 
special  fibers  in  this  nerve,  derived  from  the  chorda  tympaui. 


Fig.  4G6.  Fig.  4G7. 

Fig.  466.— Medium-sized  circumvallate  papilla  (after  Sapjiey). 

Fig.  467.— Various  kinds  of  papillae  (after  Sappey).     1,  fungiform  ;  2,  3,  4,  5,  6,  filiform  ;  7, 
hemLspherical  papillae. 

It  is  worthy  of  note  that  temperature  has  much  to  do  with 
gustatory  sensations,  a  very  low  or  a  very  high  temperature 
being  fatal  to  nice  discrimination,  and,  as  would  be  expected,  a 


Fio.  468.— Taste-buds,  from  tongue  of  rabbit  'after  Engelmann). 

temperature  not  far  removed  from  "body-heat"  (40°  C.)  is  the 
most  suitable. 

A  certain  amount  of  pressure  is  favorable  to  tasting,  as  any 
one  may  easily  determine  by  sim})ly  allowing  some  solution  of 
quinine  to  rest  on  the  tongue,  and  comparing  the  sensation  with 
tliat  resulting  when  the  same  is  rubbed  into  the  organ ;  hence 
the  importance  of  the  movements  of  the  tongue  in  appreciating 
tlie  sa])i'l  qualitifjH  of  {<)(>(]. 

Pathological  —  Among  insane    persons    hoth  olfactory  and 

40 


626 


ANIMAL  PHYSIOLOGY. 


gustatory  subjective  sensations  are  common,  and  must  be  re- 
ferred to  the  central  nervous  system. 

After  the  injection  of  some  drugs  subcutaneously,  certain 
tastes  are  experienced.  Persons  born  deficient  in  the  sense  of 
smell  to  a  marked  degree  are  very  frequently  also  wanting  in 
tasting  power. 

Comparative. — Among  the  lowest  forms  of  life  it  is  extremely 
difficult  to  determine  to  what  extent  taste  and  smell  exist  sepa- 
rately or  at  all,  as  we  can  conceive  of  them.  The  differentia- 
tion between  ordinary  tactile  sensibility  and  these  senses  has 
no  doubt  been  very  gradually  effected.  Observations  on  our 
domestic  animals  show  that  their  power  of  discrimination  by 
taste  as  well  as  by  smell  is  very  pronounced,  though  their  likes 
and  dislikes  are  so  different  from  our  own  in  many  instances. 
At  the  same  time  we  find  that  they  often  coincide,  and  it  is  not 
unlikely  that  a  dog's  power  of  discriminating  between  a  good 
beefsteak  and  a  poor  one  is  quite  equal  if  not  superior  to  man's, 
and  certainly  so  if  his  sense  of  taste,  as  in  the  human  subject, 
is  developed  in  proportion  to  his  smelling  power. 


THE  CEREBRO-SPINAL  SYSTEM  OF  NERVES. 

I.  Spinal  Nerves. 

These  (thirty-one  pairs),  which  leave  the  spinal  cord  through 
the  intervertebral  foramina,  are  mixed  nerves — i.  e.,  their  main 
trunks  consist  of  motor  and  sensory  fibers.  But  before  they 
€nter  the  spinal  cord  they  separate  into  two  groups,  which  are 


Fig.  469. — Diagram  of  roots  of  spinal  nerve  illustrating  effects  of  section  (after  Dalton).    The 
dark  regions  indicate  the  degenerated  parts. 

known  as  the  anterior  or  motor  and  the  posterior  or  sensory 
roots,  which  make  connection  with  the  anterior  and  posterior 
gray  horns  respectively. 


THE  CEREBRO-SPINAL  SYSTEM  OP  NERVES.  627 

These  facts  have  been  established  by  a  few  simple  but  im- 
portant physiological  experiments,  which  will  now  be  briefly 
described :  1.  Stimulation  of  the  peripheral  end  of  a  spinal 
nerve  gives  rise  to  muscular  movements ;  while  stimulation  of 
its  central  end  causes  pain.  2.  Upon  section  of  the  anterior 
root,  stimulation  of  its  central  end  gives  negative  results ;  but 
of  its  peripheral  end  causes  muscular  movements.  3.  After 
section  of  the  posterior  root,  stimulation  of  the  distal  end  is 
followed  by  no  sensory  or  motor  efliects ;  of  its  central  end,  by 
sensory  effects  (pain). 

These  experiments  show  clearly  that  the  anterior  roots  are 
motor,  the  posterior  sensory,  and  the  main  trunk  of  the  nerve 
made  up  of  mixed  motor  and  sensory  fibers. 

Exception. — It  has  been  found  that  sometimes  stimulation  of 
the  peripheral  end  of  the  anterior  root  has  given  rise  to  pain, 
an  effect  which  disappears  if  the  posterior  root  be  cut.  From 
this  it  is  inferred  that  certain  sensory  fibers  turn  up  into  the 
anterior  root  a  certain  distance.  Such  are  termed  "  recurrent 
sensory  fibers." 

Additional  Experiments. — 1.  It  is  found  that  if  the  anterior 
root  be  cut,  the  fibers  below  the  point  of  section  degenerate, 
while  those  above  it  do  not.  2.  On  the  other  hand,  when  the 
posterior  root  is  divided  above  the  ganglion,  the  fibers  toward 
the  cord  degenerate,  while  those  on  either  side  of  the  ganglion 
do  not.  From  these  experiments  it  is  inferred  that  the  cells  of 
the  posterior  ganglion  are  essential  to  the  nutrition  of  the  sen- 
sory fibers,  and  those  of  the  anterior  horn  of  the  cord  to  the 
motor  fibers. 

Pathological. — Pathology  teaches  the  same  lesson,  for  it  is 
observed  that,  when  there  is  disease  of  the  anterior  gray 
cornua,  degeneration  of  motor  fibers  is  almost  sure  to  follow. 
These  cells,  whether  in  the  ganglion  or  the  anterior  horn,  have 
been  termed  "  trophic."  It  is  true,  the  functions  of  the  ganglia 
on  the  posterior  roots,  other  than  those  just  indicated,  are  un- 
known ;  on  the  other  hand,  the  cells  of  the  anterior  horn  are 
distinctly  motor  in  function.  To  assume,  then,  that  the  cells 
of  the  ganglion  are  exclusively  trophic,  with  the  evidence  now 
before  us,  woiild  be  premature. 

The  view  we  hav(5  presented  of  the  relation  of  tlie  nervous 
system  makes  all  cells  trophic  in  a  certain  sense;  and  we  think 
the  view  that  certain  cells  or  certain  fibers  are  exclusively  tro- 
phic must,  as  yet,  b(;  regarded  as  an  open  (juestion. 

It  is  important,  however,  to  recognize  that  certain  connec- 


628 


ANIMAL   PHYSIOLOGY. 


tions  between  the  parts  of  the  nervous  system,  and  indeed  all 
of  the  tissues,  are  essential  for  perfect  "  nutrition,"  if  we  are  to 
continue  the  use  of  that  term  at  all. 


II.  The  Cranial  Nerves. 

These  nerves  have  been  divided  into  nerves  of  special  sense, 
motor,  and  mixed  nerves. 

The  first  class  has  already  been  considered  with  the  senses 
to  which  they  belong. 

The  physiology  of  the  cranial  nerves  has  been  worked  out 
by  means  of  sections  and  clinico-pathological  investigations. 
Speaking  generally,  a  good  knowledge  of  the  anatomy  of  these 
nerves  is  a  great  step  toward  the  mastery  of  what  is  known 
of  their  functions,  and  such  will  be  assumed  in  this  chapter,  so 
that  the  student  may  expect  to  find  the  treatment  of  the  sub- 
ject somewhat  condensed. 


Brachuim  conjunctivtim  anticum 
Brachium  conjunctivum 
posiicum 


Corpus    (anticum 
quadri-    I 
geminumiposticum 


Locus  coeruleus 
Eminentia  teres- 


Cms  cerebelh 
ad  pontem 


Ala  cinerea 
Accessorius  nucleus 


Corpus  geniculatum 
mediale 


—  Pedunculus  cerebri 


ad  corpora  qtta-j 

drigemina      f    Cms 
ad  medullam  C  cerebelli 
oblongatam  J 


Obex 
Clava 


Funiculus  cuneatus 
Funiculus  gracilis 


Fig.  470.— Intended  to  show  especially  the  origin  both  deep  and  superficial  of  cranial  nerves 
(after  Landoia).  Roman  characters  are  used  to  indicate  the  nerves  as  they  emerge,  and 
Arabic  figures  their  nuclei  or  deep  origin. 

The  Motor-Oculi  or  Third  Nerve. — With  a  deep  origin  in  the 
gray  matter  of  the  floor  and  roof  of  the  aqueduct  of  Sylvius, 


THE  CEREBRO-SPINAL  SYSTEM   OP   NERVES.  629 

branches  of  distribution  pass  to  the  following  muscles :  1.  All 
of  tbe  muscles  attached  to  the  eyeball,  with  exception  of  the 
external  rectus  and  the  superior  oblique.  2.  The  levator  pal- 
pebrse.  3.  The  circular  muscle  of  the  iris.  4.  The  ciliary- 
muscle.  Both  the  latter  branches  reach  the  muscles  by  the 
ciliary  nerves,  as  they  pass  from  the  lenticular  (ciliary,  ophthal- 
mic) ganglion.  The  relation  of  the  third  nerve,  as  seen  in  the 
changes  of  the  pupil  with  the  movements  of  the  eyeballs,  has 
already  been  noticed. 

Pathological. — It  follows  that  section  or  lesion  of  the  third 
nerve  must  give  rise  to  the  following  symptoms :  1.  Drooping 
of  the  upper  lid  (ptosis).  2.  Fixed  position  of  the  eye  in  the 
outer  angle  of  the  orbit  (luscitas).  3.  Immobility,  with  dilata- 
tion of  the  pupil  (mydriasis).     4.  Loss  of  accommodation. 

The  Trochlear  or  Fourth  Nerve.— This  nerve,  arising  in  the 
aqueduct  of  Sylvius,  passes  to  the  superior  oblique  muscle. 

Pathological. — Lesion  of  this  nerve  leads  to  peculiar  changes. 
As  there  is  double  vision,  some  alteration  must  have  occurred 
in  the  usual  position  of  the  globe  of  the  eye,  though  this  is 
not  easily  seen  on  looking  at  a  subject  thus  affected.  The 
double  image  appears  when  the  eyes  are  directed  downward, 
and  appears  oblique  and  lower  than  that  seen  by  the  unaffected 
eye. 

The  Abductor  or  Sixth  Nerve. — Arising  on  the  floor  of  the 
fourth  ventricle,  it  passes  to  the  external  rectus  of  the  eyeball, 
thus  with  the  third  and  fourth  nerve  completing  the  innerva- 
tion of  the  external  ocular  muscles  (extrinsic  muscles). 

Pathological. — Lesion  of  this  nerve  causes  paralysis  of  the 
above  -  mentioned  muscle,  and  consequently  internal  squint 
(strabismus). 

The  Facial,  Portia  Dura,  or  Seventh  Nerve. — It  arises  in  a  gray 
nucleus  in  the  floor  of  the  fourth  ventricle,  and  has  an  extensive 
distribution  to  the  muscles  of  the  face,  and  may  be  regarded, 
in  fact,  as  the  nerve  of  the  facial  muscles,  since  it  supplies, 
(1)  the  muscles  of  expression,  as  those  of  the  forehead,  eyelids, 
nose,  cheek,  mouth,  chin,  outer  ear,  etc.,  and  (2)  certain  muscles 
of  mastication,  as  the  buccinator,  posterior  belly  of  the  digastric, 
the  8tylf>hyoid,  and  also  (3)  to  the  stajoedius,  with  branches  to 
the  soft  palate  and  uvula. 

Pathological. — It  follows  that  paralysis  of  this  nerve  must 
give  rise  to  marked  facial  distortion,  loss  of  expression,  and 
flattening  of  the  features,  as  well  as  possibly  some  deficiency 
in  hearing,  smelling,  and  swallowing.     Mastication  is  difficult. 


630  ANIMAL   PHYSIOLOGY. 

and  the  food  not  readily  retained  in  the  mouth.  Speech  is 
affected  from  paralysis  of  the  lips,  etc. 

Secretory  fibers  proceed  (1)  to  the  parotid  gland  by  the  super- 
ficial petrosal  nerve,  thence  (3)  to  the  otic  ganglion,  from  which 
the  fibers  pass  by  the  auriculo-temporal  nerve  to  the  gland. 

Gustatory  Fibers.  —  According  to  some,  the  chorda  tym- 
pani  really  supplies  the  fibers  to  the  lingual  nerve  that  are  con- 
cerned with  taste. 

It  will  thus  be  seen  that  the  facial  nerve  has  a  great  variety 
of  important  functions,  and  that  paralysis  may  be  more  or  less 
.serious,  according  to  the  number  of  fibers  involved. 

The  Trigeminus,  Trifacial,  or  Fifth  Nerve. — This  nerve  has  very 
'.extensive  functions.  It  is  the  sensory  nerve  of  the  face ;  but, 
as  will  be  seen,  it  is  peculiar,  being  a  combination  of  the  motor 
and  sensory,  or,  in  other  words,  has  paths  for  both  afferent  and 
efferent  impulses.  The  motor  and  less  extensive  division  arises 
from  a  nucleus  in  the  floor  of  the  fourth  ventricle.  The  sen- 
sory, much  the  larger,  seems  to  have  a  very  wide  origin.  The 
nerve-fibers  may  be  traced  from  the  pons  Varolii  through  the 
medulla  oblongata  to  the  lower  boundary  of  the  olivary  body 
and  to  the  posterior  horn  of  the  spinal  cord.  This  origin  sug- 
gests a  resemblance  to  a  spinal  nerve,  the  motor  root  corre- 
sponding to  the  anterior,  and  the  sensory  to  a  posterior  root, 
the  more  so  as  there  is  a  large  ganglion  connected  with  the 
sensory  part  of  the  nerve  within  the  brain-case. 

Efferent  Fibers. — L  Motor. — To  certain  muscles  (1)  of  mas- 
tication— temporal,  masseter,  pterygoid,  mylohyoid,  and  the 
anterior  part  of  the  digastric.  2.  Secretory. — To  the  lachrymal 
gland  of  the  ophthalmic  division  of  this  nerve.  3,  Vaso-motor. 
— Probably  to  the  ocular  vessels,  those  of  the  mucous  mem- 
brane of  the  cheek  and  gums,  etc.  4  Trophic. — From  the  re- 
sults ensuing  on  section  of  this  nerve,  it  has  been  maintained 
that  it  contains  special  trophic  fibers.  We  have  discussed  this 
subject  in  an  earlier  chapter. 

Afferent  Fibers. — 1.  Sensory. — To  the  entire  face.  To  par- 
ticularize regions :  1.  The  whole  of  the  skin  of  the  face  and 
that  of  the  anterior  surface  of  the  external  ear.  2.  The  external 
auditory  meatus.  3.  The  mucous  lining  of  the  cheeks,  the  floor 
of  the  mouth,  and  the  anterior  region  of  the  tongue.  4.  The 
teeth  and  periosteum  of  the  jaws.  5.  The  lining  membrane  of 
the  entire  nasal  cavity.  6,  The  conjunctiva,  globe  of  the  eye, 
and  orbit.     7.  The  dura  mater  throughout. 

Many  of  these  afferent  fibers  are,  of  course,  intimately  con- 


THE   CEREBRO-SPINAL   SYSTEM   OF   NERVES. 


631 


cerned  with  reflexes,  as  sneezing,  winking,  etc.     Certain  secre- 
tory acts  are  often  excited  through  this  nerve,  as  lachrymation. 


Fig.  471.— Limits  of  cutaneous  distribution  of  sensory  nerves  to  face,  head,  and  neck  (after 
B^clanli.  1.  cutaneous  distribution  of  ophthalmic  division  of  fifth  nerve  ;  3,  of  superior 
maxillary  division  ;  3,  .3,  of  inferior  maxillary  ;  4,  of  anterior  branches  of  cervical  nerves  ; 
5,  5,  of  posterior  branches  of  cervical  nerves. 

when  the  nasal  mucous  membrane  is  stimulated ;  indeed,  the 
paths  for  afferent  impulses  giving  rise  to  reflexes,  including 
secretion,  are  very  numerous. 

Gustatory  impulses  from  the  anterior  end  and  lateral  edges 
of  the  tongue  are  conveyed  by  the  lingual  (gustatory)  branch 
of  this  nerve.  Many  are  of  opinion,  however,  that  the  fibers 
of  the  chorda  tympani,  which  afterward  leave  the  lingual  to 
unite  with  the  facial  nerve,  alone  convey  such  impressions. 
The  subject  can  not  be  regarded  as  quite  settled.  Tactile  sensi- 
bility in  the  tongue  is  very  pronounced,  as  we  have  all  experi- 
enced when  a  tooth,  etc.,  has  for  some  reason  presented  an  un- 
usual surface  quality,  and  become  a  source  of  constant  offense 
to  the  tongue. 

The  ganglia  of  the  fifth  nerve,  so  far  as  the  functions  of 
their  cells  are  concerned,  are  enigmatical  at  present.  They  are 
doubtless  in  some  sense  trophic  at  least.  With  each  of  these 
are  nerve  connections  ("roots''  of  the  ganglia),  which  seem 
to  contain  different  kinds  of  fibers.  These  ganglia  are  con- 
nected with  the  main  nerve-centers  by  both  afferent  and  efferent 
nerves,  and  also  with  the  sympathetic  nerves  themselves.  Some 
regard  the  ganglia  as  the  representatives  of  the  sympathetic 
system  within  the  cranium. 

I.  The  Ciliary  {Ophthalmic,  Lenticular)  Gancjlio n.—Ita  three 
roots  are:  1.  From  the  branch  of  the  third  nerve  to  the  inferior 


632 


ANIMAL  PHYSIOLOGY. 


oblique  muscle  (motor  root).  2.  From  the  nasal  branch,  of  the 
ophthalmic  division  of  the  fifth.  3.  From  the  carotid  plexus 
of  the  sympathetic.  The  efferent  branches  pass  to  the  iris,  are 
derived  chiefly  from  the  sympathetic,  and  cause  dilatation  of 
the  pupil.  There  are  also  vaso-motor  fibers  to  the  choroid,  iris, 
and  retina.  The  afferent  fibers  are  sen- 
sory, passing  from  the  conjunctiva,  cor- 
nea, etc. 

II.  The  Nasal  or  Spheno  -  Palatine 
Ganglion. — The  motor  root  is  derived 
from  the  facial  through  the  great  su- 
perficial petrosal  nerve ;  its  sympathetic 
root  from  the  carotid  plexus.  Both  to- 
gether constitute  the  vidian  nerve.  It 
would  seem  that  afferent  impulses  from 
the  nasal  chambers  pass  through  this 
ganglion.  The  efferent  paths  are  :  1. 
Motor  to  the  levator  palati  and  asygos 
uvulse.  2.  Vaso-motor,  derived  from  the 
sympathetic.  3.  Secretory  to  the  glands 
of  the  cheek,  etc. 

III.  The  Otic  Ganglion. — Its  roots 
are :  1.  Motor,  from  the  third  division. 
2.  Sensory,  from  the  inferior  division  of 
the  fifth.  3.  Sympathetic,  from  the 
plexus  around  the  meningeal  artery.  It 
makes  communication  with  the  chorda 
tympani  and  seventh,  and  supplies  the 
parotid  gland  with  some  fine  filaments. 
Motor  fibers  mixed  with  sensory  ones 
pass  to  the  tensor  tympani  and  tensor 
palati. 

IV.  The  Submaxillary  Ganglion. — 
Its  roots  are :  1.  Branches  of  the  chorda 
tympani,  from  which  pass  (a)  secretory 

fibers  to  the  submaxillary  and  sublingual  glands,  (b)  vaso-mo- 
tor (dilator)  fibers  to  the  vessels  of  the  same  glands.  2.  The 
sympathetic,  derived  from  the  superior  cervical  ganglion,  pass- 
ing to  the  submaxillary  gland.  It  is  also  thought  to  be  the  path 
of  vaso-constrictor  fibers  to  the  gland.  3.  The  sensory,  from 
the  lingual  nerve,  supplying  the  gland  substance,  its  ducts,  etc. 
Pathological. — 1.  The  motor  division  of  the  nerve,  when  the 
medium  of  efferent  impulses,  owing  to  central  disorder,  may 


Fig.  472.  —  Unipolar  cell  from 
Gasserian  ganglion  (after 
Schwalbe).  N,  N,  N,  nuclei 
of  sheath  ;  T,  fiber  branch- 
ing at  a  node  of  Kanvier. 


THE  CEREBRO-SPINAL  SYSTEM   OF  NERVES.  633 

cause  trismus  (locked- jaw)  from  to7iic  tetanic  action  of  the  mus- 
cles of  mastication  supplied  by  this  nerve.  2.  Paralysis  of  the 
same  muscles  may  ensue  from  degeneration  of  the  motor  nuclei 
or  pressure  on  the  nerve  in  its  course.  3.  Neuralgia  of  any  of 
the  sensory  branches  may  occur  from  a  great  variety  of  causes, 
and  often  maps  out  very  exactly  the  course  and  distribution  of 
the  branches  of  the  nerve.  4.  Vaso-motor  disturbances  are  not 
infrequently  associated  with  neuralgia.  Blushing  is  an  evi- 
dence of  the  normal  action  of  the  vaso-motor  fibers  of  the  fifth 
nerve,  o.  A  variety  of  trophic  (metabolic)  disturbances  may 
arise  from  disorder  of  this  nerve,  its  nuclei  of  origin  or  its  gan- 
glia, such  as  grayness  and  loss  of  hair  (imperfect  nutrition), 
eruptions  of  the  skin  along  the  course  of  the  nerves,  etc.  Atro- 
phy of  the  face,  on  one  or  both  sides,  gradual  and  progressive, 
may  occur.  Such  affections,  as  well  as  others,  point  in  the  most 
forcible  manner  to  the  influence  of  the  nervous  system  over  the 
metabolism  of  the  body. 

The  Glosso-pharyngeal  or  Ninth  Nerve. — This  nerve,  together 
with  the  vagus  and  spinal  accessory,  constitutes  the  eighth 
pair,  or  rather  trio.  Functionally,  however,  they  are  quite  dis- 
tinct. 

The  glosso-pharyngeal  arises  in  the  floor  of  the  fourth  ven- 
tricle above  the  nucleus  for  the  vagus.  It  is  a  mixed  nerve 
with  efferent  and  afferent  fibers :  1.  Efferent  fibers,  furnishing 
motor  fibers  to  the  middle  constrictor  of  the  pharynx,  stylo- 
pharyngeus,  levator  palati,  and  asygos  uvulae.  2.  Afferent 
fibers,  which  are  the  paths  of  sensory  impulses  from  the  base 
of  the  tongue,  the  soft  palate,  the  tonsils,  the  Eustachian  tube, 
tympanum,  and  anterior  portion  of  the  epiglottis.  Stimulation 
of  the  regions  just  mentioned  gives  rise  reflexly  to  the  move- 
ments of  swallowing  and  to  reflex  secretion  of  saliva. 

This  nerve  is  also  the  special  nerve  of  taste  to  the  back  of 
the  tongue. 

The  Pneumogastric,  Vagus,  or  Tenth  Nerve. — Most  of  the  func- 
tions of  this  nerve  have  already  been  considered  in  previous 
chapters. 

In  some  of  the  lower  vertebrates  (sharks)  the  nerve  arises 
Vjy  a  series  of  distinct  roots,  some  of  which  remain  separate 
throughout.  This  fact  explains  its  peculiarities,  anatomical 
and  functional,  in  the  higher  vertebrates.  In  these  there  have 
been  concentration  and  blending,  so  that  what  seems  to  be  one 
nerve  is  really  made  up  of  several  distinct  bundles  of  fibers, 
many  of  which  leave  the  main  trunk  later. 


634  ANIMAL  PHYSIOLOGY. 

It  may  be  regarded  as  the  'most  complicated  nerve-trunk  in 
the  hody,  and  the  distribution  of  its  fibers  is  of  the  most  exten- 
sive character.  Following  our  classification  of  efferent  and 
afferent,  we  recognize : 

1.  Efferent  fibers,  which  are  motor  to  an  extensive  tract  in 
the  respiratory  and  alimentary  regions. 

Thus  the  constrictors  of  the  pharynx,  certain  muscles  of  the 
palate,  the  oesophagus,  the  stomach,  and  the  intestine,  receive 
an  abundant  supply  from  this  source.  By  the  laryngeal  nerves, 
probably  derived  originally  from  the  spinal  accessory,  the  mus- 
cles of  the  larynx  are  innervated.  The  muscles  of  the  trachea, 
bronchi,  etc.,  are  also  supplied  by  the  pneumogastric.  It  is 
probable  that  vaso-motor  fibers  derived  from  the  sympathetic 
run  in  branches  of  the  vagus.  The  relations  of  this  nerve  to 
the  heart  and  lungs  have  already  been  explained. 

2.  Afferent  Fibers. — It  may  be  said  that  afferent  impulses 
from  all  the  regions  to  which  efferent  fibers  are  supplied  pass 
inward  by  the  vagus.  One  of  the  widest  tracts  in  the  body  for 
afferent  impulses  giving  rise  to  reflexes  is  connected  with  the 
nerve-centers  by  the  branches  of  this  nerve,  as  evidenced  by 
the  many  well-known  phenomena  of  this  character  referable 
to  the  pharynx,  larynx,  lungs,  stomach,  etc.,  as  vomiting,  sneez- 
ing, coughing,  etc.  This  nerve  plays  some  important  part  in 
secretion,  no  doubt,  but  what  that  is  has  not  been  as  yet  well 
established. 

Pathological. — Section  of  both  vagi,  as  might  be  expected, 
leads  to  death,  which  may  take  place  from  a  combination  of 
pathological  changes,  the  factors  in  which  vary  a  good  deal 
with  the  class  of  animals  the  subject  of  experiment.  Thus,  the 
heart  in  some  animals  (dog)  beats  with  great  rapidity  and 
tends  to  exhaust  itself.  In  birds  especially  is  fatty  degenera- 
tion of  heart,  stomach,  intestines,  etc.,  liable  to  follow. 

Paralysis  of  the  muscles  of  the  larynx  renders  breathing 
laborious.  From  loss  of  sensibility  food  accumulates  in  the 
pharynx  and  finds  its  way  into  the  larynx,  favoring,  if  not 
actually  exciting,  inflammation  of  the  air-passages. 

But  it  is  not  to  be  forgotten  that  upon  the  views  we  advo- 
cate as  to  the  constant  influence  of  the  nervous  system  over 
all  parts  of  the  bodily  metabolism,  it  is  plain  that  after  section 
of  the  trunk  of  a  nerve  with  fibers  of  such  wide  distribution 
and  varied  functions  the  most  profound  changes  in  so-called 
nutrition  must  be  expected,  as  well  as  the  more  obvious  func- 
tional derangements ;  or,  to  put  it  otherwise,  the  results  that 


THE  CEREBRO-SPINAL  SYSTEM  OF  NERVES.  635 

follow  are  in  themselves  evidence  of  the  strongest  kind  for  the 
doctrine  of  a  constant  neuro-metabolic  influence  which  we  ad- 
vocate. It  will  not  be  forgotten  that  the  depressor  nerve,  which 
exerts  reflexly  so  important  an  influence  over  Mood-pressure, 
is  itself  derived  from  the  vagus. 

The  Spinal  Accessory  or  Eleventh  Nerve. — This  nerve  arises 
from  the  medulla  oblongata  somewhat  far  back,  and  from  the 
spinal  cord  in  the  region  of  the  fifth  to  the  seventh  vertebra. 
Leaving  the  lateral  columns,  its  fibers  run  upward  between  the 
denticulate  ligament  and  the  posterior  roots  of  the  spinal  nerve 
to  enter  the  cranial  cavity,  which  as  they  issue  from  the  cra- 
nium subdivide  into  two  bundles,  one  of  which  unites  with  the 
vagus,  while  the  other  pursues  an  independent  course  to  reach 
the  sterno-mastoid  and  trapezius  muscles,  to  which  they  fur- 
nish the  motor  supply ;  so  that  it  may  be  considered  function- 
ally equivalent  to  the  anterior  root  of  a  spinal  nerve.  The 
portion  joining  the  vagus  seems  to  supply  a  large  part  of  the 
motor  fibers  of  that  nerve. 

Paihological. — Tonic  contraction  of  the  flexors  of  the  head 
causes  wry-neck,  and  when  they  are  paralyzed  the  head  is  drawn 
to  the  sound  side. 

The  Hypoglossal  or  Twelfth  Nerve. — It  arises  from  the  lowest 
part  of  the  calamus  scriptorius  and  perhaps  from  the  olivary 
body.  The  manner  of  its  emergence  between  the  anterior 
pyramid  and  the  olivary  body,  on  a  line  with  the  anterior  spi- 
nal roots,  suggests  that  it  corresponds  to  the  latter ;  the  more  so 
as  it  is  motor  in  function,  though  also  containing  some  vaso- 
motor fibers,  in  all  probability  destined  for  the  tongue.  Such 
sensory  fibers  as  it  may  contain  are  derived  from  other  sources 
(vagus,  trigeminus).  It  supplies  motor  fibers  to  the  tongue  and 
the  muscles,  attached  to  the  hyoid  bone. 

Paihological. — Unilateral  section  of  the  nerve  gives  rise  to 
a  corresponding  lingual  paralysis,  so  that  when  the  tongue 
is  protruded  it  j^oints  to  the  injured  side;  when  being  drawn 
in,  the  reverse.  Speech,  singing,  deglutition,  and  taste  may 
also  be  abnormal,  owing  to  the  subject  being  unable  to  make 
the  usual  co-ordinated  movements  of  the  tongue  essential  for 
these  acts. 


636 


ANIMAL  PHYSIOLOGY. 


Relations  of  the  Cerebro-spinal  and  Sympathetic 

Systems. 

No  division  of  the  nervous  system  has  been  so  unsatisfactory, 
because  so  out  of  relation  with  other  parts,  as  the  sympathetic. 
It  was  also  desirable  to  attempt  to  co-ordinate  the  cerebral  and 
spinal  nerves  in  a  better  fashion  ;  and  various  attempts  in  that 
direction  have  been  made.  Very  recently  a  plan,  by  which  the 
whole  of  the  nerves  issuing  from  the  brain  and  cord  may  be 
brought  into  a  unity  of  conception,  has  been  proposed ;  and, 
though  it  would  be  premature  to  pronounce  definitely  as  yet 
upon  the  scheme,  yet  it  does  seem  to  be  worth  while  to  lay  it 
before  the  student,  as  at  all  events  better  than  the  isolation 
implied  in  the  three  divisions  of  the  nerves  which  has  been 
taught  hitherto. 


Fig.  474. 


Fig.  473. 

Fig-  478.— Ganglion  cell  from  sympathetic  ganglion  of  frog  ;  greatly  magnified,  and  showing 

both  straight  and  coiled  fibers  (after  Quain). 
Fig.  474.— Multipolar  ganglion  cells  from  sympathetic  system  of  man,  highly  magnified  (after 

Max  Schultze).    a,  cell  freed  from  capsule  ;  6,  inclosed  within  a  nucleated  capsule.    In 

both  the  processes  have  been  broken  away. 

Instead  of  the  classification  of  nerves  into  efferent  and 
afferent,  connected  with  the  anterior  and  the  posterior  horns 


THE   CEREBRO-SPINAL  SYSTEM   OP  NERVES.  637 

of  the  gray  matter  of  the  spinal  cord,  another  division  has 
been  proposed,  viz.,  a  division  of  nerve-fibers  and  their  centers 
of  origin  in  the  gray  matter  for  the  supply  of  the  internal 
and  the  external  parts  of  the  body — i.  e.,  into  splanchnic  and 
somatic  nerves.  The  centers  of  origin  of  the  splanchnic  nerves 
are  referred  to  groups  of  cells  in  the  gray  matter  of  the  cord 
around  the  central  canal ;  while  the  somatic  nerves  spring 
from  the  gray  cornua  and  supply  the  integument  and  the 
ordinary  muscles  of  locomotion,  etc.  The  sj)lanchnic  nerves 
supply  certain  muscles  of  respiration  and  deglutition,  derived 
from  the  embryonic  lateral  plates  of  the  mesoblast ;  the  somatic 
nerves,  muscles  formed  from  the  muscle-plates  of  the  same 
region. 

It  is  assumed  that  the  segmentation  of  the  vertebrate  and 
invertebrate  animal  is  related ;  and  that  segmentation  is  pre- 
served in  the  cranial  region  of  the  vertebrate,  as  shown  by  the 
nerves  themselves. 

The  afferent  fibers  of  both  splanchnic  and  somatic  nerves 
pass  into  the  spinal  ganglion,  situated  in  the  nerve-root,  which 
may  be  regarded  as  stationary. 

It  is  different  with  the  anterior  roots.  Some  of  the  fibers 
are  not  connected  with  ganglia  at  all ;  others  with  ganglia  not 
fixed  in  position,  but  occurring  at  variable  distances  from  the 
central  nervous  system  (these  being  the  so-called  sympathetic 
ganglia) :  thus,  the  anterior  root-fibers  are  divisible  into  two 
groups,  both  of  which  are  efferent,  viz.,  ganglionated  and  non- 
ganglionated.  The  ganglionated  belong  to  the  splanchnic  sys- 
tem, and  have  relatively  small  fibers ;  the  non-ganglionated  in- 
cludes both  somatic  and  splanchnic  nerves,  composing  the 
ordinary  nerve-fibers  of  the  voluntary  striped  muscles  of  respi- 
ration, deglutition,  and  locomotion. 

It  would  appear  that  these  now  isolated  ganglia  have  been 
themselves  derived  from  a  primitive  ganglion  mass  situated  on 
the  spinal  nerves ;  so  that  the  distinction  usually  made  of  gan- 
glionated and  non-ganglionated  roots  is  not  fundamental. 

A  spinal  nerve  is,  then,  formed  of — 1.  A  posterior  root,  the 
ganglion  of  which  is  stationary  in  position,  and  connected  with 
splanchnic  and  somatic  nerves,  both  of  which  are  afferent.  2. 
An  anterior  rof>t,  the  ganglion  of  which  is  vagrant,  and  con- 
nected with  the  efferent  small-fibered  splanchnic  nerves. 

Among  the  lower  vertebrates  both  anterior  and  posterior 
roots  pass  into  the  same  stationary  ganglion.  Such  is  also  the 
case  in  the  first  two  cervical  nerves  of  the  dog. 


638  ANIMAL  PHYSIOLOGY. 

Does  the  above-mentioned  plan  of  distribution,  etc.,  bold 
for  the  cranial  nerves  ? 

Leaving  out  the  nerves  of  special  sense  (olfactory,  optic, 
and  auditory),  the  other  cranial  nerves  may  be  thus  divided : 
1.  A  foremost  group  of  nerves,  wholly  efferent  in  man,  viz., 
the  third,  fourth,  motor  division  of  the  fifth,  the  sixth,  and 
seventh.  2.  A  hindmost  group  of  nerves  of  mixed  character, 
viz.,  the  ninth,  tenth,  eleventh,  and  twelfth. 

The  nerves  of  the  first  group,  since  they  have  both  large- 
fibered,  non-ganglionated  motor  nerves,  and  also  small-fibered 
splanchnic  efferent  nerves,  with  vagrant  ganglia  (ganglion 
oculomotorii,  ganglion  geniculatum,  etc.),  resemble  a  spinal 
nerve  in  respect  to  their  anterior  roots.  They  also  resemble 
spinal  nerves  as  to  their  posterior  roots,  for  at  their  exit  from 
the  brain  they  pass  a  ganglion  corresponding  to  the  stationary 
posterior  ganglion  of  the  posterior  root  of  a  spinal  nerve. 
These  being,  however,  neither  in  roots  nor  ganglion  functional, 
are  to  be  regarded  as  the  phylogenetically  (ancestrally)  degen- 
erated remnants  of  what  were  once  functional  ganglia  and 
nerve-fibers ;  in  other  words,  the  afferent  roots  of  these  nerves 
and  their  ganglia  have  degenerated. 

The  hindmost  group  of  cranial  nerves  also  answers  to  the 
spinal  nerves.  They  arise  from  nuclei  of  origin  in  the  medulla 
and  in  the  cervical  region  of  the  spinal  cord,  directly  continu- 
ous with  corresponding  groups  of  nerve-cells  in  other  parts  of 
the  spinal  cord ;  but  in  these  nerves  there  is  a  scattering  of  the 
components  of  the  corresponding  spinal  nerves.  Certain  pecul- 
iarities of  these  cranial  nerves  seem  to  become  clearer  if  it  be 
assumed  that,  in  the  development  of  the  vertebrate,  degenera- 
tion of  some  region  once  functional  has  occurred,  in  conse- 
quence of  which  certain  portions  of  nerves,  etc.,  have  disap- 
peared or  become  functionless. 

It  is  also  to  be  remembered  that  a  double  segmentation 
exists  in  the  body,  viz.,  a  somatic,  represented  by  vertebrae  and 
their  related  muscles,  and  a  splanchnic  represented  by  visceral 
and  branchial  clefts,  and  that  these  two  have  not  followed  the 
same  lines  of  development ;  so  that  in  comparing  spinal  nerves 
arranged  in  regard  to  somatic  segments  with  cranial  nerves, 
the  relations  of  the  latter  to  the  somatic  muscles  of  the  head 
must  be  considered;  in  other  words,  like  must  be  compared 
with  like. 


THE   VOICE  AXD  SPEECH.  639 


THE  VOICE  AND  SPEECH. 

It  is  convenient  to  speak  of  the  singing  voice  and  the  speak- 
ing voice,  though  there  is  no  fundamental  difference  in  their 
production. 

Since  musical  tones  can  be  produced  by  instruments  greatly- 
resembling  those  of  the  human  voice,  it  becomes  evident  that 
in  explaining  the  human  voice  we  must  take  large  account  of 
the  principles  of  physics. 

It  is  to  be  remembered  that  sound  is  to  us  an  affection  of  the , 
nervous  centers  through  the  ear,  as  the  result  of  aerial  vibra- 
tions. 

We  are  now  to  explain  how  such  vibrations  are  caused  by 
the  vocal  mechanisms  of  animals  and  especially  of  man. 

The  tones  of  a  piano  or  violin  are  demonstrably  due  to  the 
vibrations  of  their  strings ;  of  a  clarionet  to  the  vibration  of  its 
reed.  But,  however  musical  tones  may  be  produced,  we  dis- 
tinguish in  them  differences  in  pitch,  quantity,  and  quality. 

The  pitch  is  dependent  solely  upon  the  number  of  vibrations 
within  a  given  time  as  one  second ;  the  quantity  or  loudness 
upon  the  amplitude  of  the  vibrations,  and  the  quality  upon  the 
form  of  the  vibrations.  The  first  two  scarcely  require  any  fur- 
ther notice  ;  but  it  is  rather  important  for  our  purpose  to  under- 
stand clearly  the  nature  of  quality  or  timbre,  which  is  a  more 
complex  matter. 

If  a  note  be  sounded  near  an  open  piano,  it  may  be  observed 
that  not  only  the  string  capable  of  giving  out  the  correspond- 
ing note  passes  into  feeble  vibration,  but  that  several  others 
also  respond.  These  latter  produce  the  over-tones  or  partials 
which  enter  into  notes  and  determine  the  quality  by  which  one 
instrument  or  one  voice  differs  from  another.  In  other  words, 
every  tone  is  in  reality  compound,  being  composed  of  a  funda- 
mental tone  and  overtones.  These  vary  in  number  and  in  rela- 
tive strength  with  each  form  of  instrument  and  each  voice ; 
and  it  is  now  customary  to  explain  the  differences  in  quality  of 
voices  solely  in  this  way ;  and  this  is,  no  doubt,  correct  in  the 
main ;  but  when  two  individuals,  using  successively  the  same 
violin,  play  a  scale  nearly  equal  in  loudness  and  as  much  alike 
in  all  respects  as  pc^ssiljle,  are  we  to  explain  our  ability  to  dis- 
criminate when  the  one  or  the  other  may  be  playing  (out  of 
our  sight)  solely  by  the  overtones  ?  To  answer  this  would  lead 
us  into  very  complex  considerations,  and  we  only  raise  the 


640 


ANIMAL   PHYSIOLOGY. 


question  to  keep  the  mind  of  tlie  student  open  to  new  or  pos- 
sible additional  factors  in  the  explanation. 

What  are  the  mechanisms  by  which  voice  is  produced  in 
man  ?  Observation  proves  that  the  following  are  essential :  1. 
A  certain  amount  of  tension  of  the  vocal  cords  (bands).  -  2.  A 

certain  degree  of  approximation  of 
their  edges.  3.  An  expiratory  blast 
of  air. 

It  will  be  noted  that  these  are 
all  conditions  favorable  to  the  vi- 
bration of  the  vocal  bands.  The 
greater  the  tension  the  higher  the 
pitch;  and  the  more  occluded  the 
glottic  orifice  the  more  effective 
the  expiratory  blast  of  air. 

The  principle  on  which  the  vo- 
cal bands  act  may  be  illustrated  in 
the  simplest  way  by  a  well-known 
toy,  consisting  of  an  elastic  bag  tied 
upon  a  hollow  stem  of  wood,  across 
which  rubber  bands  are  stretched, 
and  the  vibration  of  which  caused 
by  the  air  within  the  distended 
bag  gives  rise  to  the  note.  The  stu- 
dent who  would  really  understand 
the  mechanism  of  voice-production 
in  man,  should  not  only  acquire  a 
thorough  knowledge  of  the  anato- 
my of  the  larynx,  especially  of  its 
muscles  and  their  individual  ac- 
tion, but  by  means  of  the  laryngo- 
scope become  familiar  with  the  ap- 
pearances of  the  glottis  and  adja^ 
cent  parts  during  phonation.  The 
latter  is  not  difficult,  and  auto- 
laryngoscopy  or  self-examination 
may  be  made  instructive  beyond  what  can  be  indicated  in  any 
text-book. 

In  order  to  acquire  a  knowledge  of  the  human  larynx,  we 
recommend  the  dissection  of  the  larynx  of  a  pig,  this  being 
more  like  the  organ  of  man  than  is  that  of  the  sheep  or  most 
other  animals.  It  is  especially  important  to  recognize  the  na- 
ture,-extent,  and  effect  on  the  vocal  bands  of  the  movements  of 


Fig.  475 


Longitudinal  section  of  hu- 
man larynx  (after  Sappey).  1,  ven- 
tricle of  larynx  ;  2,  superior  vocal 
cord;  3,  inferior  vocal  cord;  4,  aryt- 
enoid cartilage  ;  5,  section  of  aryt- 
enoid muscle  ;  6,  6,  inferior  portion 
of  cavity  of  larynx  ;  7,  section  of 
posterior  part  of  cricoid  cartilage  ; 
a,  section  of  anterior  part  of  same  ; 
9,  superior  border  of  cricoid  car- 
tilage ;  10,  section  of  thyroid  car- 
tilage ;  11,  11,  superior  portion  of 
cavity  of  larynx  ;  13,  13,  arytenoid 
gland ;  14,  16,  epiglottis ;  15,  17, 
adipose  tissue ;  18,  section  of  hyoid 
bone ;  19,  19,  20,  trachea. 


THE  VOICE  AND  SPEECH. 


641 


Fig.  476.— Posterior  aspect  of  muscles  of  human  larynx  (after  Sappej-).  1,  posterior  crico- 
arytenoid muscle  ;  2,  3,  4,  different  fasciculi  of  arytenoid  muscle  ;  5,  aryteno-epiglottidean 
mu-scle. 

Fig.  477.— Lateral  view  of  laryngeal  muscles(after  Sappey).  1,  body  of  liyoid  bone;  2,  vertical 
section  of  thyroid  cartilage:  3,  horizontal  section  of  thyroid  cartilage,  turned  downward 
to  show  deep  attachment  of  cricothyroid  muscle  ;  4.  facet  of  the  articulation  of  small 
comu  of  thyroid  cartilage  with  cricoid  cartilage  ;  5,  facet  on  cricoid  cartilage  ;  6,  superior 
attachment  of  crico-thyroid  muscle;  7,  posterior  crico-arytenoid  muscle;  8,  lateral  crico- 
arytenoid muscle  :  9.  thyro-arytenoid  muscle  ;  10,  arytenoid  muscle  proper  ;  11,  aryteno- 
epiglottidean  muscle  ;  12,  middle  thyrohyoid  ligament ;  13,  lateral  thyro-hyoid  ligament. 

the  arytenoid  cartilages.  These  are  most  marked  around  a  ver- 
tical axis,  giving  rise  to  an  inward 
and  outward  movement  of  rota- 
tion, but  there  are  also  movements 
of  less  extent  in  all  directions.  It 
is  in  fact  through  the  movements 
of  these  cartilages  to  which  the 
vocal  bands  are  attached  posteri- 
orly, that  most  of  the  important 
changes  in  the  tension,  approxi- 
mation, etc.,  of  the  latter  are  pro- 
duced. The  lungs  are  to  be  regarded 
as  the  Vx'llows  furnishing  the  neces- 
sary wind-jjower  to  set  the  vocal 
bands  vibrating,  while  the  larynx 
lias  rf'spiratory  as  well  as  vocal 
functions,  as  has  been  already 
learned.  Assuming  that  the  stu- 
dent has  a  good  knowledge  of  the 
41 


^n/u 


Kia.  478.— I^iaryn-x,  viewed  from  above, 
on  i)artial  dissection  (after  Huxlejf). 
y/j,  thyroid  cartilage  ;  C\\  cricoid 
cartilage  ;  r,  edges  of  vocal  liga- 
ments bounding  glottis;  ylr;/,  aryte- 
noid cartilages  ;  Th.A,  thyro-aryte- 
noid iimscle ;  C.a.l.  lateral  crico- 
arytenoid TriiiKcle  ;  C.a.p,  posterior 
crico-aryteiiold  muscle  ;  /Ir.p,  pos- 
terior arytenoid  inuscles. 


642 


ANIMAL  PHYSIOLOGY. 


2     "^  2 


general  anatomy  of 
the  larynx,  we  call 
attention  briefly  to 
the  following : 

Widening  of  the 
glottis  is  effected  by 
the  crico  -  arytenoi- 
deus  posticus  pull- 
ing outward  the  pro- 
cessus vocalis  or  at- 
tachment posterior- 
ly of  the  vocal  band, 
and  a  similar  effect 
is  produced  by  the 
arytenoideus  posti- 
cus acting  alone. 

Narrowing  of  the 
glottis  is  accom- 
plished by  the  crico- 
arytenoideus  later- 
alis, and  the  follow- 
ing when  acting 
either  singly  (except 
the  arytenoideus 
posticus),  or  in  con- 
cert, as  the  sphinc- 
ter of  the  larynx, 
viz.,  the  thyro-aryt- 
enoideus  externus, 
thyro  -  arytenoideus 
internus,  thyro-ary- 
epiglotticus,  aryte- 
noideus posticus. 

Tension  of  the  vo- 
cal hands  is  brought 
about  by  the  sphinc- 
ter group,  and  espe- 
cially by  the  exter- 
nal and  internal  thy- 
ro -  arytenoid  mus- 
cles. 

Nerve  Supply. — 
The  superior  laryri- 


THE   VOICE  AND   SPEECH.  ^43 

geal  contains  the  motor  fibers  for  the  crico-th.yroid  (possibly 
also  the  arytenoidens  posticus)  and  also  supplies  the  mucous 
membrane.  The  inferior  laryngeal  supplies  all  the  other  mus- 
cles. While  both  of  these  nerves  are  derived  from  the  vagus, 
their  fibers  really  belong  to  the  spinal  accessory.  It  is  worthy 
of  note  that  the  entire  group  of  muscles  making  up  the  sphinc- 
ter of  the  larynx  is  contracted  when  the  inferior  laryngeal  is 
stimulated. 

Above  the  true  vocal  bands  lie  the  so-called  false  vocal 
bands  (cords)  which  take  no  essential  part  in  voice-production. 
Between  these  two  pairs  of  bands  are  the  ventricles  of  Morgagn  i. 
which,  as  well  as  the  adjacent  parts,  secrete  mucus  and  allow 
of  the  movements  of  both  sets  of  bands  and  in  so  far  only  as- 
sist in  phonation. 

What  is  the  nature  of  the  nervous  connections  by  which 
the  muscular  movements  necessary  for  voice-production  is  ac- 
complished. They  are  certainly  more  complex  in  nature,  at 
least  in  all  their  highest  manifestations,  than  might  at  first 
appear. 

Volition  is  unquestionably  the  starting-point,  but  the  result 
is  modified  by  a  great  variety  of  afferent  impulses,  including 
those  from  the  larynx  and  supra-laryngeal  cavities,  the  thorax, 
lungs,  even  the  ear,  and  possibly  the  eye.  Muscular  co-ordina- 
tions of  the  most  delicate  kind  must  be  effected,  seeing  the  fine 
shades  in  pitch  and  quality  which  a  first-rate  singer  can  pro- 
duce. 

To  watch,  with  the  laryngoscope,  these  changes  in  the  vocal 
bands  alone,  gives  one  an  idea  of  the  complexity  and  perfection 
of  such  adjustments  which  no  verbal  description  can  convey. 
It  is  impossible  for  a  deaf  man,  or  one  defective  in  sensibility 
in  the  regions  concerned  in  phonation,  to  produce  good  musical 
tones.  No  doubt  one  born  blind,  and  without  those  stored 
experiences  derived  from  countless  pictures,  can  but  very  im- 
perfectly make  adaptations  in  singing  dependent  on  such  ex- 
j)erience;  and  one  has  only  to  hear  deaf-mutes,  who  have 
learned  to  speak  from  imitation  of  the  speech-movements  of 
normal  persons,  to  become  convinced  of  how  important  a  part 
the  ear  plays  in  vocalization.  The  efforts  of  such  i)ersons  near- 
ly always  seem  to  be  out  of  harmony  with  the  surroundings. 

There  are  many  subjects  connected  with  the  production  of 
the  singing-voice  esp<'cially  which  have  been  matters  of  ani- 
mated (;ontrovei'sy,  (chiefly  bc(;ause  investigators  have  restricted 
their  observations  to  an  unduly  limited  range  of  facts. 


644 


ANIMAL  PHYSIOLOGY. 


The  whole  of  the  supra-laryngeal  cavities,  the  trachea  and 
bronchial  tubes,  may  be  regarded  as  resonance-chambers,  the 
former  of  which  are  of  the  most  importance,  so  far  as  the 
quality  of  the  voice  is  concerned.  There  seems  to  be  little 
doubt  that  they  have  much  to  do  with  determining  the  differ- 
ences by  which  one  individual's  voice  at  the  same  pitch  differs 
from  another ;  nor  is  the  view  that  they  may  have  a  slight  in- 
fluence on  the  pitch  of  the  voice,  or  even  its  intensity,  to  be 
ignored. 

The  epiglottis,  in  so  far  as  it  has  any  effect,  in  all  probability 
modifies  the  voice  in  the  direction  of  quality. 

The  range  of  any  one  voice  in  pitch  is,  of  course,  much  less 
than  what  may  be  termed  the  human  vocal  limit — i.  e.,  the 
range  of  the  deepest,  the  intermediate,  and  the  highest  voices 
combined. 

The  following  graphic  representation  will  serve  a  good  pur- 
pose. It  will  be  observed  that  the  extreme  limits  are  tones  of 
about  eighty  and  one  thousand  vibrations  per  second,  respect- 
ively. 

256  Soprano.  1024 


171 


Contralto. 


684 


E 


FGAT3       cdefgab       c'  d'  e' r  g'  a' h'      "^ 


5    r 


d"  e"  f"  g"  a"  b"  c' 


80 


Bass. 


342 


128 


Tenor. 


512 


Fig.  482.— This  figure  illustrates  the  range  of  the  different  kinds  of  voices,  and  the  number  of 
vibrations  answering  to  the  compass  of  each.  The  limits  here  indicated  are,  of  course,  not 
absolute. 


The  Registers  and  the  Falsetto- Voice. — Among  points  most  dis- 
puted even  yet  are  the  registers  and  the  falsetto-voice.  The 
subject  of  registers  turns  upon  the  answer  to  the  question. 
What  is  the  natural  method  of  producing  tones  ?  All  admit 
that  they  may  be  sung  with  different  vocal  mechanisms,  so  to 
speak — i.  e..  that  different  persons,  as  a  matter  of  fact,  do  not 
co-ordinate  the  various  parts  of  the  larynx  in  quite  the  same 
way.  In  attempting  to  settle  a  question  of  this  character  a 
good  deal  of  difference  in  individuality  must  be  allowed  for ; 
and,  given  equally  effective  results,  viewed  artistically,  that 


THE  VOICE  AND   SPEECH. 


645 


may  be  considered  as  the  natural  method  of  singing  a  certain 
range  of  notes  which  leads  to  the  least  expenditure  of  energy ; 
and  certain  rules  may  be  laid  down  for  the  average  man,  with, 
however,  a  good  deal  of  latitude  for  special  cases,  as  we  have 
said.     But  certainly  any  method  that  disorders  the  larynx  or 


II 


III 


Fig.  483.— Laryngoscopic  appearances  during  production  of  (I,  II)  falsetto-voice  and  (HI) 
head-tones.  I.  Falsetto  production  (after  Mandl).  II.  Falsetto  production  (after  Holmes). 
III.  Larynx  of  female  during  production  of  head-tones,  as  seen  by  the  author. 

the  general  health  can  not  be  correct.  Hence  clinical  and 
pathological  observations  become  of  great  importance.  One 
of  the  commonest  faults  consists  in  persons,  whose  laryngeal 
mechanism  does  not  permit  of  the  necessary  changes  within 
the  power  of  those  specially  endowed,  using  a  method  of  voice- 
production  for  higher  tones,  which  is  really,  in  their  case  at 
least,  adapted  only  to  lower  ones,  hence  straining,  congestions, 
fatigue,  catarrh,  and  a  host  of  attendant  evils. 

It  does  not  come  within  our  province  to  treat  of  the  artistic 
side  of  the  question ;  but  we  may  point  out  that  nearly  all  the 
compositions  of  the  greatest  masters  of  music  are  written  with- 
in a  comparatively  small  range  of  notes ;  and  when  it  is  remem- 
bered that  these  are  such  as  are  most  heard  in  the  intercourse 
of  daily  life  by  the  speaking-voice,  or  at  least  do  not  depart 
widely  from  them,  we  may  understand  how  it  is  that  such 
music  has  ever  stirred,  and  does  still  appeal  to,  the  heart  (and 
ear)  of  man  so  generally,  alike  in  the  cultivated  and  unculti- 
vated. 

Attempts  have  been  made  to  explain  the  folsetio-vnice  by 
the  action  of  the  vocal  bands  alone  ;  but  any  one  who  will  com- 
pare his  sensations,  his  consciousness  of  altered  muscular  ar- 
rangement, and  consequent  changed  relative  position  of  parts 
in  the  8ni)ra-laryiigeal  cavities,  even  without  the  use  of  a 
laryng'jscope  at  all,  can  not   fail   to  perceive  that  the  vocal 


646 


ANIMAL  PHYSIOLOGY. 


bands  are  not  alone  to  he  taken  into  account.     But  there  can 
be  no  question  of  a  very  great  difference  in  tlie  behavior  of  the 


Fig.  484. 


Fig.  483. 


Fig.  484. — Laryngoscopic  view  of  the  glottis  during  emission  of  high-pitclied  notes  (Le  Bon). 
1,  2,  base  of  tongue  ;  3,  4,  epiglottis  ;  5,  0,  pharynx  ;  7,  arytenoid  cartilages  ;  8,  opening 
between  true  vocal  cords  ;  9,  aryteno-epiglottidean  folds  ;  10,  cartilage  of  Santorini ;  11, 
cuneiform  cartilage  ;  12,  superior  vocal  cords;  13.  inferior  vocal  cords  (bands). 

Fig.  485.— Glottis  as  seen  by  laryngoscope  during  production  of  chest-voice  (.after  Mandl  and 
Griitzner). 

vocal  bands  in  the  production  of  the  falsetto  as  compared  with 
the  chest  voice. 

As  has  been  suggested,  in  the  higher  tones  of  the  falsetto, 
the  vocal  bands  are  shortened  and  come  together  posteriorly,  at 
all  events ;  and  this  may  be  produced  largely  by  the  action  of  the 
thyro-arytenoideus  internus,  and  possibly  several  other  mus- 
cles. There  is  little  doubt  that  the  whole  breadth  of  the  bands 
does  not  share  in  the  vibrations.  In  many  of  its  features,  the 
high  falsetto  of  the  male  voice  is  allied  in  production  to  the 
head-voice  of  females,  in  which  only  the  central  parts  of  the 
bands  seem,  in  the  highest  notes,  to  be  involved. 

In  nearly  all  previous  considerations  of  this  topic,  it  seems 
to  us  that  insufficient  attention  has  been  paid  to  the  method  of 
applying  the  blast  of  air  by  the  lungs.  The  great  importance 
of  this  in  playing  wind-instruments  is  practically  recognized, 
yet  in  our  own  wind-instrument,  the  most  perfect  of  all,  it  has 
received  too  little  practical,  and  still  less  theoretical,  attention. 

Pathological — The  results  of  the  paralysis  of  the  several 
muscles  of  the  larynx,  of  the  soft  palate,  etc.,  throw  a  certain 
amount  of  light  upon  this  subject;  it  is  not  to  be  forgotten, 
however,  that  in  this  instance,  as  in  others,  the  usual  (normal) 
mechanism  may  be  obscured  through  adaptations  by  unusual 
methods,  so  that  the  best  is  made  of  a  bad  case : 

1.  When  the  widening  of  the  glottis  can  not  take  place,  and 
the  glottic  opening  assumes  the  cadaveric  position,  owing  to  pa- 
ralysis of  the  crico-arytenoidei  postici,  there  may  be  dyspnoea. 
2.  Paralysis  of  the  arytenoideus  transversus,  in  consequence  of 


THE  VOICE  AND  SPEECH.  647 

which  the  glottic  opening  can  not  be  sufficiently  narrowed, 
allows  of  undue  escape  of  air,  and  gives  rise  to  feebleness  and 
harshness  of  tlie  voice.  3.  There  may  be  almost  complete  loss 
of  voice  from  paralysis  of  both  thyro-arytenoid  muscles.  4. 
When  the  crico-thyroid  muscles  are  paralyzed,  owing  to  im- 
perfect tension  of  the  vocal  bands,  the  voice. may  become  lower 
pitched  and  harsh.  Any  form  of  paralysis  of  the  vocal  bands 
should  arrest  attention  and  lead  to  a  careful  examination  of  the 
chest  for  aneurism,  etc.,  and  to  general  inquiry,  for  even  the 
brain  may  be  involved. 

The  importance  of  the  muscles,  by  which  the  larynx  is  raised 
and  steadied,  must  not  be  overlooked.  In  professional  singers 
from  constant  practice  they  often  become  greatly  enlarged. 
We  may  here  remark  upon  the  value  of  singing  when  not 
pushed  to  the  verge  of  fatigue,  when  free  from  straining,  and 
in  a  pure  atmosphere,  as  a  healthful  exercise,  the  whole  of 
which  does  not  consist  in  the  good  arising  from  the  use  of  the 
chest,  larynx,  etc.,  or  the  additional  amount  of  oxygen  respired, 
but  also  from  complicated  and  ill-understood  nervous  effects. 

At  puberty,  in  both  sexes,  the  larynx  shares  in  those  changes 
of  relative  and  absolute  size  which  the  body  then  experiences 
so  generally.  The  thickening  from  excess  of  blood  and  nerv- 
ous energy  produces,  especially  in  youths,  a  harsh  voice,  which 
is,  in  this  instance,  as  in  all  others,  an  indication  of  the  need 
of  rest  of  the  parts.  To  sing  under  such  circumstances  is,  of 
course,  liable  to  induce  permanent  injury  in  the  form  of  weak- 
ness or  harshness  of  voice ;  but  once  this  period  is  passed,  regu- 
lar vocal  gymnastics  may  be  of  great  service  in  perfecting  an 
organ  unrivaled  as  a  musical  instrument,  and  by  means  of 
which  man  is  raised  through  the  endowment  of  speech  vastly 
above  all  other  animals. 

The  subject  of  voice  production  and  voice  preservation  is 
one  of  the  utmost  importance  in  education,  though  it  receives 
comparatively  little  attention.  The  public  taste  for  high- 
pitched  vocalization  does  unquestionably  tend  to  ruin  voices, 
and  is  alike  opposed  to  artistic  and  physiokjgical  principles. 
While  a  few  may  reach  the  prescribed  standard  of  the  public 
taste,  the  many  fail  in  the  attempt. 

Comparative. — Much  more  is  known  of  the  sounds  emanating 
from  tli(;  lower  animals  than  of  the  mechanisms  by  which  they 
are  produced.  This  ap])lies, of  course, especially  to  such  sounds 
as  are  not  produced  by  external  parts  of  tht;  body,  it  being 
very  difficult  to  investigate  these  experimentally  or  to  observe 


648 


ANIMAL   PHYSIOLOGY. 


the  animal  closely  enough  when  producing  the  various  vocal 
effects  naturally. 

All  of  our  domestic  mammals  have  vocal  bands  and  a  larynx, 
not  as  widely  different  from  that  of  man  as  might  be  supposed 
from  the  feeble  range  of  their  vocal  powers. 

The  actual  behavior  of  the  vocal  bands  has  been  studied 
experimentally  in  the  dog  when  growling,  barking,  etc.  And, 
so  far  as  it  goes,  this  mechanism  of  voice  production  is  not 
essentially  different  from  that  of  man.  Growling  is  the  result 
of  the  functional  activity  of  the  vocal  mechanism,  not  unlike 
that  of  man  when  singing  a  bass  note ;  barking,  of  that  analo- 
gous to  coughing  or  laughing,  when  the  vocal  bands  are  rapidly 
approximated  and  separated. 

The  grunting  of  hogs  and  the  lowing  and  bawling  of  horned 
cattle  is  i3robably  very  similar  in  production,  so  far  as  the 
larynx  is  concerned,  to  the  above.  The  cat  has  plainly  very 
great  command  over  the  larynx,  and  can  produce  a  wide  range 
of  tones. 

The  quality  of  the  voice  of  most  animals  appears  harsh  to 
our  ears,  owing  probably  to  a  great  preponderance  of  over-tones, 
in  consequence  of  an  imperfect  and  unequal  tension  of  the  vocal 

bands ;  but  the  influence  of  the  su- 
pra-laryngeal  cavities,  often  very 
large,  must  also  be  taken  into  ac- 
count. 

In  certain  of  the  primates,  and 
especially  in  the  howling  monkeys, 
large  cheek-pouches  can  be  inflated 
with  air  from  the  larynx,  and  so  add 
to  the  intensity  of  the  note  produced 
by  the  vocal  bands  that  their  voice 
may  be  heard  for  miles.  Song-birds 
produce  their  notes,  as  may  be  seen, 
by  external  movements  low  down  at 
the  bifurcation  of  the  trachea  (sy- 
rinx). The  notes  are  owing  to  the 
vibration  of  two  folds  of  the  mucous 
membrane,  which  project  into  each 
bronchus,  and  are  regulated  in  their 
movements  by  muscles,  the  bronchial  rings  in  this  region  being 
correspondingly  modified. 

A  large  number  of  species  of  fishes  produce  sounds  and  in 
a  variety  of  ways,  in  which  the  air-bladder,  stomach,  intestines. 


Fig.  486. — Lower  larynx  (Syrinx)  of 
crow  (after  Gegenbaur).  A,  seen 
from  side  ;  B,  seen  from  in 
front,  a—/,  muscles  concerned 
in  movements  of  lower  larynx  ; 
fif,  membrana  tympaniformis  in- 
terna, stretching:  from  median 
surface  of  either  bronchus  to  a 
bony  ridge  (pessulus)  which  pro- 
jects at  the  angle  of  bifurcation 
of  trachea. 


THE  VOICE   AND  SPEECH. 


649 


etc.,  take  part.  Most  reptiles  are  voiceless,  in  the  proper  sense, 
though  there  are  few  that  can  not  produce  a  sort  of  hissing 
sound,  caused  by  the  forcible  emission  of  air  through  the  upper 
respiratory  passages. 

Frogs,  as  is  well  known,  produce  sounds  of  great  variety  in 
pitch,  quality,  and  intensity,  some  species  croaking  so  as  to  be 
heard  at  the  distance  of  at  least  a 
mile.  It  is  a  matter  of  easy  ob- 
servation that  when  frogs  croak 
the  capacity  of  the  mouth  cavity 
is  greatly  increased,  owing  to  dis- 
tention of  resonating  sacs  situated 
at  each  angle  of  the  jaws.  When 
tree-frogs  croak,  their  throats  are 
greatly  distended,  apparently  in 
successive  waves.  But  it  is  among 
insects  that  the  greatest  variety 
of  methods  of  producing  sounds  is 
found. 

In  bees  and  flies  sounds  are 
caused  by  the  vibration  of  mus- 
cular reeds  placed  in  the  stigmata 
or  openings  of  their  tracheal  tubes, 
also  by  the  extremely  rapid  vibra- 
tion of  their  wings.  The  death- 
head  moth  is  said  to  force  air  from 
its  sucking  stomach,  and  thus  give 
rise  to  a  sound  in  the  same  way 
as  certain  fishes. 

In  the  grasshopper  a  noise  is 
produced  by  rubbing  its  rough 
legs  against  the  wing-cases,  and  in  allied  forms  (locusts)  by 
moving  the  wing-cases  against  one  another ;  and  in  other  groups 
<lifferent  parts  of  the  body  are  brought  into  mutual  contact  or 
rubbed  or  struck  against  foreign  bodies. 


Fig.  487.— Portion  of  trachea  or  air-tube 
of  a  caterpillar  (after  Gegenbaur). 
u.  epithelial-like  cellular  layer ;  ft, 
nuclei.  The  air-tubes  in  insects  ai'e 
kept  up  by  coiled  chitinous  tubes, 
as  .seen  above  ;  ai  d,  like  the  blood- 
vessels of  mammals,  penetrate  every 
part  of  the  body.        , 


Speech. 


It  may  be  noticed  that  the  differences  of  voices,  by  which 
we  are  enabled  to  discriminate  between  individuals,  are  much 
more  marked  during  speaking  than  singing.  This  is  owing  to 
^eater  yjrominence  of  over-tones  in  the  speaking  voice,  as  may 
be  readily  shown. 


650  ANIMAL  PHYSIOLOGY. 

If  a  series  of  tuning-forks  be  held  before  the  open  mouth, 
it  will  be  found  that  but  one  position  of  the  buccal  cavity  and 
its  contents  answers  to  a  certain  note,  but  that  when  this  is 
assumed  it  acts  as  a  resonance-chamber;  thus,  for  a  tuning- 
fork  sounding  A,  when  the  cavity  takes  the  shape  necessary 
to  sound  (speak)  that  note,  the  tone  produced  by  the  fork  is 
greatly  augmented  when  the  latter  is  held  before  the  mouth. 
It  has  thus  been  estimated  that  the  fundamental  tones  of  the 
vowel  cavity  are  these :  U  =  b,  O  =  b',  A  =  b'",  I  =  b"".  If  the 
vowels  of  this  series  be  whispered,  their  pitch  rises.  Whisper- 
ing may  be  termed  speech  without  voice — i.  e.,  the  vocal  bands 
do  not  vibrate,  but  the  total  effect  is  produced  by  the  blast  of 
air  acting  through  the  supra-laryngeal  parts  as  a  resonance 
cavity. 

Now,  if  it  be  true  that  there  is  but  one  position  of  the  supra- 
laryngeal  cavities  that  will  give  a  pure  vowel-sound,  and  this 
sound  corresponds  in  pitch  to  a  certain  note  of  the  scale,  it 
seems  to  us  that  the  conclusion  that  the  pitch  of  the  voice,  as 
well  as  its  quality,  is  dependent  to  some  extent  upon  these  parts 
as  well  as  the  vocal  bands.  Such  a  view  is,  however,  not  that 
generally  taught.  Every  singer  knows  that  it  is  impossible  to 
produce  certain  vowel-sounds  pure  with  notes  of  a  certain  pitch. 
Usually,  when  the  nasal  cavity  is  shut  off  posteriorly  by  the 
soft  palate,  or  stopped  anteriorly  by  closing  the  nostrils,  a 
change  in  quality  of  the  vowel-sounds,  characterized  as  nasal, 
is  produced  ;  but,  as  illustrating  well  that  the  organism  has 
more  ways  than  one  of  accomplishing  the  larger  part  if  not  all 
its  ends,  by  effort,  and  especially  by  practice,  the  vowels  may 
be  sounded  nearly  as  well  as  usual  under  these  unfavorable 
conditions. 

Consonants. — The  sounds  produced  by  the  vocal  bands  may 
be  modified  by  interruption  in  their  formation  or  otherwise, 
though  it  is  plain,  from  what  has  been  said,  that  the  form  of 
the  mouth,  etc.,  can  not  be  ignored  in  any  form  of  vocalization. 

According  to  the  parts  of  the  supra-laryngeal  cavities  con- 
cerned in  the  modification  referred  to,  may  we  have  the  basis 
of  a  physiological  classification  of  the  consonants,  though  it  is 
obvious  that  they  may  be  dealt  with  on  wholly  different  prin- 
ciples. By  the  first  method,  which  alone  chiefly  concerns  us, 
we  have  a  division  into  labials,  dentals,  and  gutturals,  according 
as  the  lips,  teeth,  or  soft  palate  and  pharynx  are  chiefly  con- 
cerned. Of  course,  several  parts  are  involved  in  all  sound-pro- 
duction, and  we  recommend  the  student  to  resort  to  the  forma- 


THE   VOICE  AND  SPEECH.  651 

tion  of  the  vowels  and  consonants  before  a  mirror,  in  order  to 
acquire  a  practical  knowledge  of  the  relative  share  taken  by 
the  different  parts  of  the  supra-laryngeal  vocal  organs.  Ordi- 
narily the  tongue  does,  of  course,  function  as  the  most  impor- 
tant organ  of  speech ;  but  the  extent  to  which  this  organ,  the 
front  teeth,  the  lips,  etc.,  can  by  practice  be  dispensed  with  is 
surprising  in  the  extreme.  Persons  with  more  than  half  of  the 
tongue  removed  manage  to  speak  quite  intelligibly. 

Consonants  may  be  further  classified  according  to  the  nature 
of  the  movements  associated  with  their  formation  :  thus,  they 
may  be  either  continuous  or  explosive,  the  meaning  of  which 
■will  be  clear  from  the  classification  given  below,  and  the  basis 
of  the  latter  from  an  inspection  of  the  parts  by  a  mirror  dur- 
ing their  formation,  supplemented  by  consultation  of  our  sen- 
sations at  the  time. 

The  following  tabulation  may  be  of  service,  as  representing 
at  least  certain  aspects  of  the  subject : 

Explosives :  Labials,  P,  B. 
Dentals,  T,  D. 
Gutturals,  K,  G. 

Aspirates :     Labials,  F,  V. 

Dentals,  L,  S,  Sh,  Th,  Z. 

Gutturals,  Cli  (as  in  loch),  Gh  (as  in  laugh). 

Resonants :    Labials,  M. 
Dentals,  N. 
Gutturals,  N,  G. 

Vibratory :    Labial. 

Dental,  R  (common). 
Guttural,  R  (guttural). 

It  is  remarkable  that  certain  consonantal  (and  vowel)  sounds 
are  wholly  absent  from  some  languages.  All  are  familiar  with 
the  difficulty  Europeans  find  in  sounding  the  English  th,  as  in 
thin.  Their  vocal  organs  fail  to  make  the  necessary  co-ordina- 
tions, these  not  having  been  practised  in  youth. 

Pathological. — Paralysis  of  the  soft  palate,  giving  rise  to  a 
na.sal  quality  of  voice,  illustrates  the  importance  of  this  little 
muscular  curtain. 

Stammering  is  believed  to  be  caused  by  long-continued 
spasm  of  the  diaphragm — in  other  words^  u])on  tonic  contrac- 
tion of  this  musclci  in  the  inspiratory  position,  usually  (le2)end- 
ent  on  some  form  of  psychic  excitement.  Stuttering,  on  the 
other  hand,  is  tem])orary  inability  to  form  the  sounds  desired; 
lack  of  co-ordination  of  parts  principally.     The  various  paraly- 


652  ANIMAL   PHYSIOLOGY. 

ses  of  tlie  vocal  bands  affect  speech  as  well  as  voice,  though 
to  a  less  extent;  and  whispering  is,  of  course,  always  possible. 

Special  Considerations  and  Summary. 

Evolution. — The  very  lowest  forms,  and  in  fact  most  inverte- 
brate groups,  seem  to  be  voiceless.  Darwin  has  shown  that 
voice  is,  in  a  large  number  of  groups,  confined  either  entirely 
to  the  male,  or  that  it  is  so  much  more  developed  in  him  as  to 
become  what  he  terms  a  "  sexual  character."  There  is  abundant 
evidence  that  males  are  chosen  as  mates  by  the  females,  among 
birds  especially,  not  alone  for  superiority  in  beauty  of  plumage, 
but  also  for  their  song.  Thus,  by  a  process  of  natural  selection 
(sexual  selection),  the  voice  would  tend  to  improve  with  the 
lapse  of  time,  if  we  admit  heredity,  which  is  an  undeniable  fact, 
even  among  men — whole  families  for  generations,  as  the  Bachs, 
having  been  musicians. 

One  can  also  understand  why  on  these  principles  voice 
should  be  especially  developed  in  certain  groups  (birds),  while 
among  others  (mammals)  form  and  strength  should  determine 
sexual  selection,  the  strongest  winning  in  the  contests  for  the 
possession  of  the  females,  and  so  propagating  their  species  under 
the  more  favorable  circumstances  of  chance  of  the  most  desira- 
ble females. 

Pathology  teaches  that,  when  certain  parts  of  the  brain 
(speech-centers)  of  man  are  injured  by  accident  or  disease,  the 
power  of  speech  may  be  lost.  From  this  it  is  evident  that  the 
vocal  apparatus  may  be  perfect  and  yet  there  be  no  speech ;  so 
that  it  becomes  comprehensible  that  the  vocal  powers  of,  e.  g., 
a  dog,  are  so  limited,  notwithstanding  his  comparatively  highly 
developed  larynx.  He  lacks  the  energizing  and  directive  ma- 
chinery situated  in  the  brain. 

Some  believe  that  there  was  a  period  when  man  did  not  pos- 
sess the  power  of  speech  at  all ;  and  many  are  convinced  that 
the  human  race  has  undergone  a  gradual  development  in  this 
as  in  other  respects.  Certain  it  is  that  races  differ  still  very 
widely  in  capacity  to  express  ideas  by  spoken  words. 

We  may  regard  the  development  of  a  race  of  speaking  ani- 
mals as  dependent  upon  a  corresponding  advance  in  brain- 
structure,  whether  that  was  acquired  by  a  sudden  and  pro- 
nounced variation,  or  by  gradual  additions  of  increase  in  cer- 
tain regions  of  the  brain,  or  whether  to  the  first  there  was  then 
added  the  second. 


THE  VOICE  AND  SPEECH.  653 

It  is  not  unlikely  that,  whether  sexual  selection  has  played 
any  considerable  part,  natural  selection  at  all  events  has  had 
not  a  little  to  do  with  the  preservation  of  those  individuals 
and  races  that  soonest  and  most  fully  developed  the  speech-cen- 
ters ;  for  it  is  to  be  remembered  that  the  principle  of  correlated 
growth  must  be  taken  into  account.  In  nature  generally,  as  in 
social  life,  success  very  frequently  leads  to  success.  As  man's 
superiority  over  the  highest  of  the  mammals  below  him  is 
largely  due  to  his  possession  of  a  speaking  (and  writing)  faculty, 
so  must  we  concede  that  racial  superiority  is  in  part  traceable 
to  the  same  cause.  It  is  well  known  that  the  leaders  among 
savage  tribes  are  frequently  effective  in  speech  as  well  as  strong 
of  heart  and  arm. 

This  subject  is  a  very  large,  suggestive,  and  complex  one, 
and  is  worthy  of  some  thought. 

Apart  from  speech  proper,  there  is  a  language  of  the  face 
and  body  generally,  in  which  there  is  much  that  we  share  with 
lower  forms,  especially  lower  mammals.  Darwin,  noticing  this 
resemblance,  regarded  it  as  evidence  strengthening  the  belief 
that  man  is  derived  from  lower  forms.  Why  should  the  forms 
of  facial  expression  associated  with  certain  emotions  so  widely 
among  different  races  of  men  be  so  similar  to  each  other  and 
to  those  which  the  lower  animals  employ,  if  there  is  not  some 
community  of  origin  ?  This  is  Darwin's  query,  and  he  con- 
sidered, as  has  been  stated,  that  the  answer  to  be  given  was  in 
harmony  with  his  views  of  man's  origin,  as  based  on  an  alto- 
gether different  sort  of  testimony. 

The  high  functional  development  of  the  hand  and  arm  in 
man,  and  the  use  of  these  parts  in  writing,  are  suggestive. 

Summary. — The  musical  tones  of  the  voice  are  caused  by  the 
vibrations  of  the  vocal  bands,  owing  to  the  action  on  them  of 
an  expiratory  blast  of  air  from  the  lungs.  In  order  that  the 
bands  may  act  effectively,  they  must  be  rendered  tense  and  ap- 
proximated, which  is  accomplished  by  the  action  of  the  laryn- 
geal muscles,  especially  those  attached  to  the  arytenoid  car- 
tilages. We  may  speak  of  the  respiratory  glottis  and  the 
vocalizing  glottis,  according  as  we  consider  the  position  and 
movements  of  the  vocal  bands  in  respiration  or  in  phonation. 

The  pitcli  of  tiie  voice  is  determined  by  the  length  and  the 
tension  of  the  vocal  bands,  and  frequently  both  shortening  and 
increased  tension  are  combined  ;  perhaps  we  may  say  that  al- 
tered (not  necessarily  increa.sed)  tension  and  length  are  always 
combined. 


654  ANIMAL  PHTSIOLOaY. 

The  quality  of  the  voice  depends  chiefly  upon  the  supra- 
laryngeal  cavities. 

The  vocal  bands  of  the  child  and  of  woman,  being  both 
shorter  and  lighter,  account  largely  for  the  differences  in  pitch, 
quality,  and  loudness  of  their  voices  as  compared  with  that  of 
man.  Success  in  vocalization  is  dependent,  not  only  on  a  suit- 
able laryngeal  and  other  mechanism,  but  upon  the  rapidity  and 
completeness  with  which  a  large  number  of  muscular  and  nerv- 
ous co-ordinations  can  be  made.  Speech  may  be  either  reflex 
or  voluntary,  but  for  high-class  results  many  afferent  impulses 
must  determine  or  modify  the  nature  of  the  efferent  impulses. 

There  is  no  essential  difference  in  the  mechanism  of  the 
speaking  and  singing  voice ;  in  the  latter,  however,  the  vocal 
bands  take  a  relatively  greater  share  than  in  the  former,  in 
which  the  supra-laryngeal  parts  are  more  concerned.  This 
applies  especially  to  the  utterance  of  consonants,  which  may 
be  classified  according  to  the  part  of  the  above-mentioned  ap- 
paratus that  is  more  especially  employed. 

It  is  important  to  remember  that  in  all  phonation,  in  the 
case  of  man  at  least,  many  parts  combine  to  produce  the  result ; 
so  that  voice-production  is  complex  and  variable  in  mechan- 
ism, beyond  what  would  be  inferred  from  the  apparent  sim- 
plicity of  the  mechanism  involved ;  while  the  central  nervous 
processes  are,  when  comparison  is  made  with  phonation  in 
lower  animals,  seen  to  be  the  most  involved  and  important  of 
the  whole — a  fact  which  the  results  of  disease  of  the  brain  are 
well  calculated  to  impress,  inasmuch  as  interruptions  anywhere 
among  a  class  of  cerebral  connections,  now  known  to  be  very  ex- 
tensive, suffice  to  abolish  voice,  and  especially  speech-production. 

It  is  of  great  practical  moment  for  each  individual  to  recog- 
nize both  the  limit  of  his  natural  powers,  especially  of  his 
range  in  singing,  and  at  the  same  time  to  appreciate  the  large 
margin  there  is  for  improvement,  more  particularly  when  cul- 
tivation of  the  voice  is  commenced  in  childhood,  and  resumed 
soon  after  the  age  of  puberty  is  attained. 

Among  mammals  below  man  the  vocal  bands  and  laryngeal 
and  thoracic  mechanism  are  very  similar,  but  less  perfectly 
and  complexly  co-ordinated ;  so  that  their  vocalization  is  more 
limited  in  range,  and  their  tones  characterized  by  a  quality 
which  to  the  human  ear  is  less  agreeable.  Man's  superiority 
as  a  speaking  animal  is  to  be  traced  chiefly  to  the  special  de- 
velopment of  his  cerebrum,  both  generally  and  in  certain 
definite  regions. 


LOCOMOTION.  655 


LOCOMOTION. 

The  entire  locomotor  system  of  tissues  is  derived  from  tlie 
em.bryonic  mesoblast.  These  include  the  muscles,  bones,  carti- 
lage, and  connective  and  fibrous  tissues ;  and  the  tissues  that 
make  up  the  vascular  system  or  the  motor  apparatus  for  the 
circulation  of  the  blood.  Locomotion  in  the  mammal  is  effected 
by  the  movement  of  certain  bony  levers,  while  the  equilibrium 
of  the  body  is  maintained.  The  whole  series  of  levers  is  bound 
together  by  muscles,  tendons,  ligaments,  etc.,  and  play  over 
one  another  at  certain  points  where  they  are  invested  with  car- 
tilage, and  kept  moist  by  a  se- 
cretion from  the  cells  covering  ^  r  B 
the  synovial  membranes  that  | 
form  the  inner  linings  of  joints. 

Cartilage,  a  very  low  form 
of  tissue  destitute  of  blood-ves- 


FiG.  488. 

sels,  and  hence  badly  repaired 
when  lost  by  injury  or  disease, 
forms  a  series   of   smooth  sur-      p  ^ 

faces    admirably     adapted    for     ^aa""'""" ifKt <> p '"iiiii"ii'iiiiii,!iMini' 

joints,  and  especially  fitted  to 
act  as  a  series  of  elastic  buffers, 
and  thus  prevent  shocks.  Bone, 
though  brittle  in  the  dried  state, 
possesses,  when  alive,  a  favora- 
ble degree  of  elasticity,  while 
sufficiently  rigid.  Provision  is 
made  by  its  vascular  periosteum       V Ta  b 

•!  / .  1  "i"i»'ii»M.ii mil »iMiiii.iii,ii„ iiii.iiiiiiiiiii.ij 

and  central  marrow  (m  the  case        v  | 

of  the  long  bones),  as  well  as  by 
the  blood-supply  derived   from  fig.  490. 

the  nutrient  artery  and  its  rami- 
fications throughout  the  osseous  tissue,  for  abundant  nourish- 
ment, growth,  and  repair  after  injury. 

We  find  in  the  body  of  mammals,  including  man,  examples 
of  all  three  kinds  of  levers.  It  sometimes  happens  that  there 
is  an  apparent  sacrifice  of  energy,  the  best  leverage  not  being 
exemplified  ;  but  on  closer  examination  it  will  be  seen  tliat  the 
weight  must  either  be  moved  with  nice  precision  or  through 
large  distances,  and  these  objects  can  not  be  accomplished  al- 
ways by  the  arrangements  that  would  simply  furnish  the  most 


656 


ANIMAL   PHYSIOLOGY. 


powerful  lever.     This  is  illustrated  by  the  action  of  the  biceps 
on.  the  forearm. 

It  is  to  be  remembered  that,  while  the  flexors  and  extensors 
of  a  limb  act  in  a  certain  degree  the  opposite  of  one  another. 


Fig.  491.— Skeleton  of  deer.  The  bones  in  the  extremities  of  th's  the  fleetest  of  quadrupeds 
are  inclined  very  obliquely  toward  each  other  and  toward  the  scapular  and  iliac  bones. 
This  arrangement  increases  the  leverage  of  the  muscular  system  and  confers  great 
rapidity  on  the  moving  parts.  It  augments  elasticity,  diminishes  shocli,  and  indirectly 
begets  continuity  of  movement,  a,  angle  formed  by  femur  with  ilium  ;  b.  angle  formed 
by  tibia  and  fibula  with  femur  ;  c,  angle  formed  by  phalanges  with  cannon-bone  ;  e,  angle 
formed  by  humerus  with  scapula  ;  /,  angle  formed  by  radius  and  ulna  with  humerus 
(Pettigrew). 

there  is  also,  in  all  cases  perhaps,  a  united  action ;  the  one 
set,  however,  preponderating  over  the  other,  and  usually  sev- 
eral muscles,  whether  of  the  same  or  different  classes,  act 
together. 

Standing  itself  requires  the  exercise  of  a  large  number  of 
similar  and  antagonistic  muscles  so  co-ordinated  that  the  line 
of  gravity  falls  within  the  area  of  the  feet.  An  unconscious 
person  falls,  which  is  itself  an  evidence  of  the  truth  of  the 
above  remarks. 

The  following  statements  in  regard  to  the  direction  of  the 
line  of  gravity  may  prove  useful :  1.  That  for  the  head  falls  in 
front  of  the  occipital  articulation,  as  exemplified  by  the  nod- 
ding of  the  head  in  a  drowsy  person  occupying  the  sitting  atti- 
tude. 2.  That  for  the  head  and  trunk  together  passes  behind  a 
line  joining  the  centers  of  the  two  hip-joints,  hence  the  uncor- 
rected tendency  of  the  erect  body  of  man  is  to  fall  backward. 
3.  That  for  the  head,  trunk,  and  thighs  falls  behind  the  knee- 


LOCOMOTION. 


657 


joints  somewhat,  which  would  also  favor  falling  backward 
(bending  of  the  knees).  4.  The  line  of  gravity  of  the  whole 
body  passes  in  front  of  a  line  joining  the  two  ankle-joints,  so 
that  the  body  would  tend,  but  for  the  contraction  of  the  mus- 
cles of  the  calves  of  the  legs,  to  fall  forward. 

Taking  these  different  facts  into  consideration  explains  the 
various  directions  in  which  an  individual,  when  erect,  may  fall 
according  as  one  or  the  other  line  (center)  of  gravity  is  dis- 
placed for  a  long  enough  time. 

Walking  (man)  implies  the  alternate  movement  of  each  leg 
forward,  pendulum-like,  so  that  for  a  moment  the  entire  body 


Fig.  492.— Shows  the  simultaneous  positions  of  both  legs  during  a  step,  divided  into  four 
groups  (after  Weber).  First  group  (.4),  4  to  7,  gives  the  different  positions  which  the  legs 
simultaneouslv  a.ssume  while  both  are  on  the  ground;  second  group  (J?),  8  to  11,  shows 
the  various  piisitions  of  both  legs,  at  the  time  when  the  posterior  leg  is  elevated  from  the 
ground,  but  behind  the  supported  one;  third  group  (C),  12  to  14,  shows  the  positions 
which  the  legs  a.ssume  when  th<'  swinging  leg  overtakes  the  standing  one  ;  and  the  fourth 
group  (D),  1  to  .3.  the  positions  during  the  time  when  the  swinging  leg  is  propelled  in 
advance  of  the  resting  one.  The  letters  a.  h,  and  c  indicate  the  angles  formed  by  the 
bones  of  the  right  leg  when  engaged  in  making  a  step  j  the  letters  m,  ji,  and  o,  the  posi- 
tions assumed  by  the  right  foot  when  the  trunk  is  rolling  over  it ;  g,  shows  the  rotating 
forward  of  the  trunk  upon  the  left  foot  (/)  as  an  axis  ;  h,  shows  the  rotating  forward  of 
the  left  leg  and  foot  upon  the  trunk  (a)  as  an  axis. 


Fio.  493.— Overliand  swimming  (Pettigrew). 


must  be  supported  on  one  foot.     When  the  right  foot  is  lifted 
or  swung  forward,  the  left  must  support  the  weight  of  the 

42 


658 


ANIMAL  PHYSIOLOGY. 


Fig.  494.— Runner  provided  with  apparatus  intended  to  register  his  different  paces  (Marey). 

body.     It  becomes  oblique,  the  heel  being  raised,  the  toe  still 
resting  on  tlie  ground ;  and  it  is  upon  this  as  a  fulcrum  that 


Fig.  495.— Instrument  to  register  vertical  reactions  during  various  paces  (Blarey). 


LOCOMOTION. 


659 


tlie  body- weight  is  moved  forward,  when  a  similar  action  is 
taken  up  by  the  opposite  leg. 

It  follows  that  to  prevent  a  fall  there  must  be  a  leaning  of 
the  body  to  one  side,  so  that  the  line  of  gravity  may  pass 
through  each  stationary  foot.  It  follows  that  a  walking  person 
describes  a  series  of  vertical  curves  with  the  head,  and  of  hori- 
zontal ones  with  the  body,  the  resulting  total  being  complex. 

The  peculiarities  of  the  gait  of  different  jjersons  are  natu- 
rally determined  by  their  height,  length  of  leg,  and  a  variety 
of  other  factors,  which  are  often  inherited  with  great  exactness. 
We  instinctively  adopt  that  gait  which  economizes  energy, 
both  physical  and  mental. 

Running  differs  from  walking,  in  that  both  feet  are  for  a 
period  of  the  cycle  off  the  ground  at  the  same  time,  owing  to 
a  very  energetic  action  of  the  foot  acting  as  a  fulcrum. 

Jumping  implies  the  propulsion  of  the  body  by  the  impulse 
given  by  both  feet  at  the  same  moment. 

Hopping  is  the  same  act  accomplished  by  the  use  of  one 
leg. 

Comparative. — The  movements  of  quadrupeds  are  naturally 
very  complicated,  but  have  now  been  well  worked  out  by 


..-.^■y 


:Jjd 


a  : 


F108.  A'Mi  and  4»7.— Showing  the  more  or  less  perpendicular  direction  of  the  stroke  of  the  wing 
in  the  flight  of  tht-  bird  (giill):  how  the  wing  is  gradually  extended  as  it  is  elevated  (e,/,  g): 
how  it  descends  as  a  long  lever  until  it  assumes  the  pf>sition  indicated  by  h  ;  how  it  is 
flexed  toward  the  termination  of  the  down-stroke,  as  shown  at  A,  i.  7,  to  convert  it  into  a 
short  lever  (a,  b)  and  prepare  it  for  making  the  upstroke.  The  difference  in  the  length  of 
the  wing  during  flexion  and  extension  is  indicated  by  the  short  and  long  levers  a,  b  and 
c,  (I.  The  sudden  conversion  of  the  wing  from  a  long  into  a  short  lever  at  the  end  of  the 
down-stroke  in  of  great  importance,  as  ft  robs  the  wing  of  its  momentum  and  i)repares  it 
for  reversing  its  movements)  (Pettigrew). 


the  use  of  instantaneous  photograi)hy.  Even  the  T)ird's  flight 
is  no  longer  a  wholly  unsolved  problem,  but  is  fairly  well 
understood.  The  movements  of  centipeds  and  other  many- 
legged  invertebrates  are  highly  complicated,  while  their  rapid 


660 


ANIMAL  PHYSIOLOGY. 


Figs.  498  and  499  show  that  when  the  wings  are  elevated  (e.  /,  g),  the  body  falls  (s) ;  and  that 
when  the  wings  are  depressed  {h,  i,  j),  the  body  is  elevated  (r).  Fig.  498  shows  that  the 
wings  are  elevated  as  short  levers  (e)  until  toward  the  termination  of  the  up-stroke,  when 
they  are  gradually  expanded  (/,  gr)  to  prepare  them  for  making  the  down-stroke.  Fig.  499 
shows  that  the  wings  descend  as  long  level's  (h)  until  toward  the  termination  of  the  down- 
stroke,  when  they  are  gradually  folded  or  flexed  {i,  j)  to  rob  them  of  their  momentum  and 
prepare  them  for  making  the  up-stroke.  Compare  with  Figs.  496  and  497.  By  this  means 
the  air  beneath  the  wings  is  vigorously  seized  during  the  down-stroke,  while  that  above  it 
is  avoided  during  the  up-stroke.  The  concavo-convex  form  of  the  wings  and  the  forward 
travel  of  the  body  contributes  to  this  result.  The  wings,  it  will  be  observed,  act  as  a  para- 
chute both  during  the  up  and  down  strokes.  Fig.  499  shows  also  the  compound  rotation 
of  the  wing,  how  it  rotates  upon  a,  as  a  center,  with  a  radius  m,  b,  n,  and  upon  a,  c,  6  as 
a  center,  with  a  radius  k,  I  (Pettigrew). 

movements  are  to  be  accounted  for  by  the  multiplicity  of  their 
levers  rather  than  the  rapidity  with  which  they  are  moved. 


Fig.  500.— Chilhngham  bull  (Bos  Scoticiis).  Shows  powerful  heavy  body,  and  the  small 
extremities  adapted  for  land  transit.  Also  the  figure-of-8  movements  made  by  the  feet 
and  limbs  in  walking  and  running,  xt,  i,  curves  made  by  right  and  left  anterior  extremi- 
ties ;  ?-,  .s,  curves  made  by  right  and  left  posterior  extremities.  The  right  fore  and  the 
left  hind  foot  move  together  to  form  the  waved  line  (s,  u) ;  the  left  fore  and  the  right  hind 
foot  move  together  to  form  the  waved  hne  (r,  t).  The  curves  formed  by  the  anterior  if,  u) 
and  posterior  (r,  s)  extremities  form  ellipses  (Pettigrew). 


LOCOMOTION. 


661 


The  lengtli  and  flexibility  of  their  bodies  must  also  be  taken 
into  account,  rendering  many  legs  necessary  for  support.    We 


Fig.  501.— Representation  of  horse  at  walking  pace  (Marey). 


can  only  briefly  refer  to  tbe  method  of  locomotion  well  exem- 
plified by  our  domestic  quadrupeds.  However,  the  whole  sub- 
ject will  become  plainer  after  a  careful  study  of  the  cuts  intro- 
duced in  this  chapter. 


Fio.  602.— Horse  in  act  of  trotting.  In  this,  as  in  all  the  other  paces,  the  body  of  the  horse  Is 
lev<rre'l  forward  by  a  (iiiiKorial  twistinR  of  tnink  antl  extremities,  the  extremities  describ- 
ing a  flgure-of-H  trat^k  in  u.  r  ti  The  flgiire-of-H  is  produced  by  the  alternate  jilay  of  the 
extremiti<-«  and  feet,  two  of  wiiicli  are  always  on  tiie  ground  (a,  /*).  Thu.s  tlie  right  fore- 
t<Kit  deH<-rit>es  the  curve  marked  f.  the  Jeft  hind-foot  tiiat  marked  r,  left  fore-foot  that 
marked  u.  and  rigiit  iiinrl-fcxit,  s.  The  feet  on  ground  in  the  present  instance  are  left  fore 
and  right  hind  (I'ettigrewj. 


662 


ANIMAL   PHYSIOLOGY. 


In  walking,  quadrupeds  like  the  horse  use  the  limbs  alter- 
nately, and  in  a  diagonal  sequence,  so  that  the  right  fore-leg 


Fig.  503. — Red-throated  dragon  (Draco  hcematopogon.  Gray),  shows  a  large  membranous 
expansion  (b,  b)  situated  between  anterior  (d,  d )  and  posterior  extremities,  and  supported 
by  the  ribs.    The  dragon  by  this  arrangement  can  take  extensive  leaps  with  perfect  safety. 

Fig.  504. — Flying  lemur  (Galeopithecus  volans,  Shaw).  In  the  flying  lemur  the  membranous 
expansion  (a,  b)  is  more  extensive  than  in  the  flying  dragon.  It  is  supported  by  the  neck, 
back,  and  tail,  and  by  the  anterior  and  posterior  extremities.  The  flying  lemur  takes 
enormous  leaps  ;  its  membranous  tunic  all  but  enabling  it  to  fly.  The  bat,  Phyllorhina 
gracilis  (Fig  505),  flies  with  a  very  sUght  increase  of  surface.  The  surface  exposed  by  the 
bat  exceeds  that  displayed  by  many  insects  and  birds.  The  wings  of  the  bat  are  deeply 
concave,  and  so  resemble  the  wings  of  beetles  and  heavy-bodied,  short-winged  birds.  The 
bones  of  the  arm  (r).  forearm  (d),  and  hand  ()i,  n,  n)  of  the  bat  support  the  anterior  or 
thick  margin  and  the  extremity  of  the  wing,  and  may  not  inaptly  be  compared  to  the 
nervures  in  corresponding  positions  in  wing  of  beetle  (Pettigrew). 

and  the  left  hind-leg  are  associated.     Trotting  corresponds  to 
running  in  man,  and  there  is  the  same  diagonal  action.     There 


Fig.  505. — The  bat  (Phyllorhina  gracilis,  Peters).  Here  the  traveling-surfaces  (rdef,  annn) 
are  enormously  increased  as  compared  with  that  of  the  land  and  water  animals  generally 
(Pettigrew).    r,  arm  ;  d,  forearm  ;  ef,nn  n,  hand  of  bat. 

is  also  a  gait  natural  to  some  horses,  some  dogs,  the  camel,  etc., 
termed  ambling,  or  pacing,  characterized  by  both  legs  on  the 
same  side  working  simultaneously  and  alike.  This  is  perhaps 
comparable  to  human  walking.  In  galloping,  all  four  feet  are 
off  the  ground  together  for  a  portion  of  the  cycle,  though  they 
do  not  strike  the  ground  again  at  the  same  moment. 

Evolution. — It  is  noteworthy  that  with  almost  all  quadrupeds 
the  gallop  is  the  natural  method  for  rapid  propulsion.     In  all 


MAN   CONSIDERED  PHYSIOLOGICALLY.        .  663 

animals,  either  bred  by  man  to  attain  great  speed,  as  the  race- 
horse and  greyhound,  or  those  that  have  become  so  by  the  pro- 
cess of  natural  selection,  the  entire  conformation  of  the  body 
has  been  modified  in  harmony  with  the  changes  that  have  taken 
place  in  the  legs  and  feet.  This  is  seen  in  the  greyhound  among 
domestic  animals,  and  in  the  wild  deer  of  the  plain  and  forest. 
Such  instances  illustrate  not  only  the  principle  of  natural  se- 
lection as  a  whole,  but  the  subordinate  one  of  correlated 
growth. 

Any  one  observing  the  modes  of  locomotion  of  quadrupeds, 
especially  horses  and  dogs,  will  perceive  the  advantages  of  the 
four-legged  arrangement.  Not  only  is  there  a  variety  of  modes 
of  progression,  as  walking,  trotting,  galloping,  cantering,  the 
alternations  of  which  permit  of  rest  to  certain  groups  of  mus- 
cles, with  their  corresponding  nervous  connections,  etc.,  but  on 
occasion  some  of  these  animals  can  progress  fairly  well  with 
three  legs.  Sometimes  it  may  also  be  noticed  that  a  horse  that 
prefers  one  gait,  as  pacing,  for  his  easy,  slow  movements/  will 
break  into  a  trot  when  pushed  to  a  higher  rate  of  speed. 

Trotting  can  not  be  considered  the  natural  gait  for  high 
speed  in  the  horse,  yet,  by  a  process  of  "  artificial  selection " 
(by  man)  from  horses  that  have  shown  capacity  for  great  speed 
by  this  mode  of  progression,  strains  of  racers  have  been  bred, 
showing  that  even  an  acquired  mode  of  locomotion  may  be 
hereditary ;  while  that  galloping  is  the  more  natural  mode  of 
locomotion  of  the  horse  is  evident,  among  other  things,  by  the 
tendency  of  even  the  best  trotting  racers  to  break  into  a  gallop 
when  unduly  pushed — an  instance  also  of  an  hereditary  tend- 
ency of  more  ancient  origin  prevailing  over  one  more  recent. 

Tlie  bipedal  modes  of  progression  of  birds  are  naturally 
very  like  those  of  man. 


MAN  CONSIDERED  PHYSIOLOGICALLY  AT  THE  DIFFERENT 
PERIODS  OF  HIS  EXISTENCE. 

Growth. — As  a  result  of  the  intra-uterine  development  of 
two  cells,  neither  of  which  is  visible  by  the  naked  eye,  the 
human  being  reaches  about  one  third  of  its  total  length  and 
one  twentieth  of  its  maximum  weight.  In  the  infant  the  rela- 
tively larger  size  of  the  head  and  face  is  obvious,  while  among 
internal  organs  the  liver  is  especially  large.  The  child's  future 
increase  in  weight  is  chiefly  from  growth  of  muscles.     Increase 


664  .  ANIMAL  PHYSIOLOGY. 

in  stature  continues  up  to  about  the  twenty-fifth,  year,  though 
the  increase  is  most  rapid  during  infancy  and  puberty,  when, 
in  fact,  the  weight  is  also  greatly  augmented. 

Digestive  System. — While  it  is  now  established  that  all  of  the 
digestive  secreting  mechanisms  are  active  at  or  shortly  after 
birth,  it  must  be  borne  in  mind  that  these,  like  the  other  organs, 
adapt  gradually  to  the  new  conditions.  This  is  a  matter  of 
practical  importance  in  infant  feeding.  Thus,  while  it  is  true 
that  the  young  infant's  saliva  will  act  on  starch,  it  is  not  to  be 
supposed  that  its  amylolytic  powers  are  equal  to  those  of  the 
adult. 

Circulatory  and  Respiratory  Systems.  —  The  babe's  heart  is 
larger  than  that  of  the  adult  relatively  to  its  body-weight,  and 
its  action  more  rapid ;  hence  the  circulation  is  accomplished  in 
a  shorter  space  of  time,  an  advantage  when  it  is  considered  that 
the  need  for  oxygen  and  tissue-food  in  the  young  organism  is 
so  great. 

The  respirations  are  correspondingly  rapid,  and  the  actual 
amount  of  the  respiratory  interchanges  is  greater  than  in  adult 
life.  There  appears,  however,  to  be  a  storing  up  of  oxygen — 
i.  6.,  all  of  the  oxygen  used  up  does  not  shortly  appear  again  as 
carbonic  anhydride. 

The  metabolism  of  the  infant  is  very  active,  and  is  spent 
largely  in  construction ;  growth  is  in  excess  of  waste ;  indeed, 
this  feature  is  characteristic  of  the  metabolism  of  all  young 
animals.  There  is,  in  consequence  of  the  excessive  loss  of  heat, 
from  a  relatively  larger  surface  than  in  the  adult,  the  need  for 
a  more  active  metabolism ;  the  young  animal  must  eat  more, 
to  meet  this  waste.  It  is,  moreover,  in  consequence  of  this  fact 
that  infants,  when  not  protected  better  than  adults,  perish  from 
a  fall  in  the  temperature,  which  their  sensitive  organizations 
can  not  endure. 

Immediately  after  birth  the  adaptation  to  the  new  environ- 
ment is  less  perfect  than  at  a  later  period ;  respiration  is  feeble ; 
the  blood  is  imperfectly  aerated ;  the  temperature  is  lower ;  the 
entire  metabolism  goes  on  but  feebly :  hence  it  is  that  newly 
born  kittens,  puppies,  etc.,  can  be  immersed  in  water  for  a  con- 
siderable period  (twenty  to  thirty  minutes)  without  drowning. 
The  tissues  do  not  demand  much  oxygen ;  they  live  on  what 
they  already  have  stored  up,  after  that  in  the  blood  is  ex- 
hausted— in  a  word,  they  behave  much  as  they  did  during  intra- 
uterine life.  The  excretions,  as  would  be  supposed  from  the 
rapid  metabolism,  are  more  abundant  than  in  the  adult.    There 


MAN  CONSIDERED   PHYSIOLOGICALLY.  665 

is  more  urine  passed  and  more  urea  excreted  in  proportion  to 
the  weight.  , 

The  lymphatic  system,  as  a  whole,  is  more  pronounced  in 
youth.  Certain  glands,  the  functions  of  which  are  not  well 
understood,  for  which  reason  we  have  thought  it  well  to  pass 
them  over  entirely,  are  at  their  highest  development  during 
infantile  life,  as  the  thymus  and  thyroid.  These  atrophy  as 
puberty  approaches,  especially  the  thymus  gland. 

The  prominence  of  the  lymphatic  sj^stem  harmonizes  with 
what  we  know  of  the  functions  of  the  colorless  corpuscles  of 
the  blood  in  the  work  of  building  up  tissues.  They  may  be  re- 
garded as  remnants  of  embryonic  life,  undifferentiated  cells 
awaiting  their  opportunity  to  develop,  though  we  do  not,  of 
course,  mean  to  affirm  that  in  the  blood  and  elsewhere  they 
have  no  other  functions ;  in  fact^,  it  has  been  shown  that  in  the 
alimentary  tract  they  are  porters  of  digestive  products  (fat, 
etc.) ;  and  they  also  likely  play  an  important  part  as  scavengers 
and  as  guardians  of  the  nobler  cells  against  micro-organisms, 
etc. 

Dentition. — The  change  in  the  metabolic  powers  of  the  ani- 
mal is  foreshadowed  by  the  gradual  appearance  of  teeth  for  the 
preparation  of  a  more  solid  food  to  meet  the  altered  wants  of 
the  economy. 

The  first  appearance  of  teeth  is  in  the  upper  jaw,  the  two 
central  incisors,  soon  to  be  followed  by  the  corresponding  ones 
of  the  lower  jaw.  This  is  at  about  the  seventh  or  eighth 
month,  to  be  succeeded  by  the  lateral  incisors  a  couple  of 
months  later ;  the  first  molars  about  the  end  of  the  first  year  of 
life ;  the  canines  (eye-teeth)  half  a  year  later ;  and  the  whole  of 
the  temporary  set  before  the  second  year  is  completed. 

The  permanent  teeth  replace  the  milk-teeth  very  gradually, 
and  are  thus  adapted  to  the  growing  jaws.  The  new  dentition 
begins  to  appear  about  the  sixth  year,  and  may  continue  for 
six  or  eight  years.  The  last  molar  (wisdom  tooth)  appears  very 
late,  between  the  seventeenth  and  the  twenty-fifth  year.  It  is 
noteworthy  that  this  tooth  seems  to  be  more  and  more  delayed, 
and  often  never  appears  at  all,  which  may  be  said  of  some 
others,  especially  the  lateral  incisors ;  so  that  it  looks  as  if,  as 
civilization  progressed,  the  jaw  were  becoming  smaller  and  the 
teeth  suffering  atrophy.  Both  the  teeth  and  the  hair  are  epi- 
dermic structures,  and  their  defective  growth  at  the  present 
time  in  so  many  individuals  raises  suggestive  questions.  The 
face  of  civilized  man  seems  also  to  be  getting  smaller  relatively 


QQQ  ANIMAL  PHYSIOLOGY. 

to  the  head.  Is  this  an  example  of  correlated  growth,  to  be 
explained  by  the  predominance  of  the  cerebrum  ? 

Nervous  System. — The  nervous  system,  like  all  the  others,  is 
highly  sensitive ;  it  reacts  powerfully  to  moderate  stimuli ;  its 
equilibrium  is  more  readily  disturbed  than  that  of  any  other ; 
and,  since  to  it  belongs  the  work  of  guiding  the  metabolic  pro- 
cesses of  the  various  tissues,  this  peculiarity  explains  the  readi- 
ness with  which  the  health  of  the  infant  can  be  deranged  or 
restored.  Hence  it  follows  that  a  prognosis  in  the  case  of  in- 
fants must  be  unusually  guarded. 

As  has  been  already  indicated,  the  cortical  cells  of  the  cere- 
brum, and  other  parts  of  the  brain,  are  but  indifferently  devel- 
oped at  birth ;  so  that  stimulation  of  the  cerebral  surface  in 
young  animals  (though  there  is  great  difference  in  this  respect) 
must  not  be  expected  to  give  precisely  the  same  results  as  in 
adults. 

From  the  share  that  we  now  know  the  cortex  of  the  cere- 
brum to  take  in  the  elaboration  of  probably  all  sensory  im- 
pulses, it  follows  that  in  the  infant  all  of  the  senses  must  be  to 
a  certain  extent  imperfect,  even  assuming  that  the  peripheral 
mechanisms  are  as  perfect  functionally  as  in  the  adult,  which 
is  not  likely. 

In  some  respects,  however,  the  eye  of  the  infant  is  more 
perfect.  Its  power  of  accommodation  for  near  objects  is  won- 
derful, while  at  a  very  early  age  the  pupil  acts  perfectly,  and 
binocular  vision  is  established. 

Touch  is  fairly  developed,  and  probably  also  taste  and 
smell ;  though  as  to  the  last  two  there  is  more  doubt.  On  the 
other  hand,  hearing  in  the  infant  is  very  imperfect ;  power  to 
discriminate  between  the  pitch  and  quality  of  sounds  is  rudi- 
mentary ;  while  appreciation  of  direction,  which  is  largely  the 
result  of  experience,  is  necessarily  of  the  crudest. 

It  is  doubtful  if  the  middle  ear  is  properly  pervious  to  air, 
on  which  its  functioning  depends  greatly  for  some  time  after 
birth.  But  certainly,  as  regards  the  processes  of  the  peripheral 
mechanisms  of  the  senses,  the  child  that  has  passed  the  years 
of  infancy  knows  a  perfection,  to  which  he  becomes  more  and 
more  a  stranger  as  years  pass  by.  Later  he  will,  in  consequence 
of  accumulating  experience,  make  more  out  of  his  sensory 
data ;  his  cerebral  cortex  will  be  more  developed,  both  struct- 
urally and  functionally. 

Maturity  (Puberty). — Though  most  of  the  organs  of  the  body 
continue  to  improve,  and  certainly  the  organism,  as  a  whole. 


MAN  CONSIDERED   PHYSIOLOGICALLY.  667 

up  to  about  the  fortieth  year  of  life  or  later,  puberty  is  that 
period  of  life  which  is  most  remarkable  for  sudden,  striking  de- 
velopment. While  this  is  in  some  respects  most  pronounced  in 
the  sexual  organs  and  related  parts,  as  the  pelvis  and  mammary 
glands  of  the  female,  yet  a  whole  host  of  other  changes  take 
place  simultaneously,  in  such  a  way  as  to  leave  no  doubt  that 
they  are  related  to  those  of  the  sexual  organs.  Not  only  the 
characteristic  form  of  the  body,  but  the  psychic  peculiarities  of 
the  sexes,  appear  and  become  fully  established  with  an  extraor- 
dinary rapidity. 

There  is,  therefore,  no  period  of  life  fraught  with  so  much 
of  developmental  good  or  ill  as  puberty.  A  host  of  diseases 
may  now  show  themselves,  according  to  the  laws  of  heredity, 
as  a  result  of  deficient  resistance,  etc. 

The  Sexes. — While  the  differentiation  of  sex  becomes  greatly 
more  pronounced  at  puberty,  there  are  decided  differences  be- 
tween the  male  and  female  infant.  The  male  from  birth  is  the 
taller  and  the  heavier.  This  inequality  is  maintained  in  adult 
life.  The  average  woman  is  shorter  and  lighter  than  the  man ; 
her  muscular  and  bony  systems  are  less  developed,  both  abso- 
lutely and  relatively;  her  brain  is  some  ounces  lighter;  her 
blood  is  poorer  in  haemoglobin,  of  lighter  specific  gravity,  and, 
as  a  whole,  less  in  quantity.  Woman's  metabolism,  if  we  may 
judge  by  the  income  and  expenditure,  is  both  absolutely  and 
relatively  less.'  Man's  physical  strength  is  nearly  double  that 
of  woman. 

These  facts  have  an  important  bearing  on  some  of  the  burn- 
ing questions  of  the  day.  There  are,  it  will  be  seen,  deep-lying 
differences  between  the  sexes,  which  can  not  be  ignored  in  our 
education  and  civilization  generally,  without  running  counter 
to  that  sexual  differentiation  which  Nature,  through  long  ages, 
has  been  bringing  toward  higher  and  higher  development. 

Old  Age. — From  middle  life  onward,  in  most  persons,  there 
is  a  gradual  process  of  deterioration  going  on  in  every  tissue. 
Elasticity  diminishes  and  rigidity  of  tissues  becomes  more  and 
more  marked.  The  arteries  undergo  changes  which,  whether 
fatty  or  calcareous,  greatly  impair  their  usefulness ;  the  carti- 
lages of  the  ribs  and  other  parts  tend  to  become  calcareous,  so 
that  the  chest- walls  possess  less  of  elasticity ;  this,  combined 
with  a  general  impairment  of  muscular  power,  lessens  the 
capability  of  thoracic  movement.  Protoplasm  everywhere  has 
less  vital  potential,  so  to  speak ;  hence  with  the  approach  of  old 
age  we  often  find  adipose  tissue  in  excess.     It  becomes  a  bur- 


668  ANIMAL  PHYSIOLOGY. 

den  to  an  already  weakened  organism.  Nervous  discharges 
tend  more  and  more  to  be  slow,  weak,  and  to  take  the  lines 
fixed  by  long  usage ;  hence,  perhaps,  that  undue  conservation 
of  mind  common  to  the  old ;  that  lack  of  enterprise,  which  is 
strengthened  by  the  consciousness  of  inability,  physical  and 
mental,  for  the  strain  of  new  undertakings.  Hence  also  the 
natural  failure  of  acquiring  power  and  the  memory.  The 
judgment,  dependent  as  it  is  on  accumulating  experience,  im- 
proves. With  extreme  old  age  there  is  a  reversion  to  the 
infantile  condition,  marked  by  irritability  of  tissues,  weak- 
ness, etc. 

The  laws  of  habit  and  rhythm  are  illustrated  abundantly 
in  the  subjects  we  have  been  considering.  Rhythm  seems  to 
be  a  sort  of  key-note  to  the  interpretation  of  the  universe ;  but 
since  we  have  frequently  referred  to  this  subject  throughout 
the  volume,  it  will  not  be  further  dwelt  upon  now. 

Comparative,  —  All  mammals  have  their  periods  of  rapid 
growth,  slower  decay,  and  death.  Their  growth  is  usually 
more  rapid  than  man's,  and  as  their  whole  lives  are  shorter, 
with  few  exceptions,  their  rate  of  decay  is  faster.  There  are 
great  differences  between  various  mammals  in  their  degree  of 
development  at  birth.  Among  some  (the  marsupials)  they 
separate  from  the  mother  internally,  to  become  attached  to  the 
nipples  externally  when  very  imperfectly  developed.  Though 
puppies,  kittens,  and  other  members  of  the  groups  to  which 
they  belong  (cornivora)  are  born  with  the  eyes  unopened,  no 
mammal  is  so  helpless  as  the  human  infant  when  ushered  into 
the  world.  Most  animals  learn  the  use  of  their  muscles,  and  to 
provide  for  themselves  in  a  very  short  period.  Slowness  of 
development  is,  however,  even  among  the  lower  animals,  fre- 
quently associated  with  the  attainment  of  an  ultimately  higher 
functional  status,  and  the  precocious  child  should  be  the  object 
of  some  anxiety.  It  may  develop  into  a  prodigy  of  talent,  rise 
little  above  mediocrity,  or  become  the  subject  of  some  serious 
or  fatal  form  of  disease. 

It  is  important  to  recognize  that  sexual  maturity,  in  the 
sense  of  ability  to  produce  ripe  ova  and  spermatozoa,  does  not 
correspond  with  the  full  development  of  the  animal ;  so  that  it 
may  be  as  unscientific  to  breed  together  animals  that  are  very 
young  as  those  that  are  decaying  from  age.  Especially  is  it 
undesirable  to  mate  two  very  young  or  very  old  animals.  Such 
a  principle  applies,  of  course,  also  to  man. 

Death. — If  the  continuance  of  life  is  dependent  on  the  cease- 


MAN  CONSIDERED   PHYSIOLOGICALLY.  669 

less  adaptation  of  internal  to  external  conditions,  it  becomes 
clear  that  death  may  be  said  to  be  ever  imminent ;  and  in  the 
highest  mammals  the  vital  organism  is  so  complex  and  so 
delicately  balanced,  that  it  is  marvelous  that  life  lasts  so  long 
as  it  does.  Few  animals  i^erish  from  simple  decay  leading  to  a 
gradual  slowing  of  the  vital  machinery,  down  to  zero,  so  to 
speak ;  but  when  death  is  not  due  to  violence,  as  it  frequently 
is,  it  rather  arises  from  some  essential  part  getting  out  of  gear, 
either  directly  or  indirectly.  So  great  is  the  need  of  a  constant 
supply  of  free  oxygen  in  the  mammal,  that  an  arrest  of  the 
respiration  always  implies  a  stoppage  of  the  circulation.  These 
results  may  be  brought  about  by  the  direct  action  of  poisoned 
blood  on  the  heart,  or  on  the  nervous  centers  presiding  over 
lungs,  heart,  and  other  organs.  Death  may  then  be  due  to 
central  influences,  though  finally  the  arrest  of  the  circulation 
is  the  real  proximate  cause.  When  the  circulation  is  so  ar- 
rested that  it  can  not  be  started  again,  somatic  or  body  death 
must  follow,  which  is  to  be  distinguished  from  the  death  of 
the  individual  tissues. 

Somatic  death  marks  the  first  stage  of  the  return  of  a  vital 
organism  toward  the  inorganic  world,  whence  it  was,  in  a 
sense,  derived.  That  molecular  arrangement  or  movement 
peculiar  to  living  things  once  being  permanently  deranged, 
its  resolution  into  the  less  complex  forms  of  the  inorganic 
compounds  speedily  follows,  though  the  rate  will  depend  much 
upon  circumstances  in  any  individual  case.  Life  is  much 
more  of  a  mystery  than  death.  Physiology  attempts  to  de- 
fine the  conditions  under  which  life  exists,  but  can  not  explain 
life  itself.    Will  it  ever  lift  the  veil  ? 


APPENDIX. 


ANIMAL  CHEMISTRY. 

An  attempt  will  be  made  in  this  chapter  to  give  a  brief  account  of 
the  principal  substances  entering  into  or  derivable  froin  the  mammalian 
body,  or  resulting  from  its  metabolism.  We  may  repeat  that,  inasmuch 
as  chemical  treatment  kills  living  organisms,  we  can  only  know  the 
chemical  constitution  of  the  dead  body. 

The  cells  and  tissues  of  the  body  of  a  mammal  are  made  up  of  pi'oto- 
plasm,  which  belongs  to  that  large  class  of  bodies  known  as  proteids. 
However,  it  is  seldom,  if  ever,  that  pure  protoplasm  is  found,  for  even 
in  the  youngest  cells  and  in  unicellular  animals  and  plants  this  sub- 
stance usually  contains  some  representatives  of  the  class  of  bodies  known 
as  carbohydrates  and  fats.  Protoplasm  is,  moreover,  the  producer  or 
builder  of  both  fats  and  carbohydrates,  as  has  been  already  learned.  In 
one  sense  all  the  chemistry  of  the  body  is  the  chemistry  of  protoplasm, 
in  that  it  is  either  by  one  or  other  phase  of  the  metabolism  of  cells  that 
the  various  secretions,  excretions,  and  reserve  products  of  cells  arise. 
We  have  already  considered  this  aspect  of  the  subject  in  connection 
with  the  treatment  of  the  metabolism  of  the  animal  body,  and  shall 
now  direct  attention  in  more  detail  to  certain  chemical  facts,  groupings, 
and  principles,  largely  with  the  purpose  of  illustrating  the  resemblances 
between  the  products  of  our  laboratories  and  of  our  bodies.  At  the 
same  time  it  is  to  be  l>orne  in  mind,  as  we  have  often  remarked  in  the 
main  body  of  the  work,  that  we  are  generally  unable  to  say  whether  the 
syntheses  and  analyses  of  the  body  resemble  those  made  by  the  chemist 
in  the  laboratory  or  not.  Indeed,  the  whole  subject,  from  this  point  of 
view,  is  as  yet  in  a  very  crude  condition. 


PROTEIDS. 

These  include  a  large  class  of  bodies  as  yet  very  imperfectly  under- 
st4->od  chemically.  According  to  Hoppe-Seyler,  the  following  percentage 
compfjsition  ruay  be  assigned  to  them  : 

O  N  H  C  S 

20  9-23  5.  ic-2-170,  dH-T^,  r,ir,^r>4r,,  oa-20. 

Usually  on  ignition  a  very  small  quantity  of  ash  remains. 


672  ANIMAL  PHYSIOLOGY. 

Proteids  are  amorphous  ;  insoluble  in  alcohol  and  ether  ;  some  of 
them  soluble  in  water  ;  soluble  with  change  of  constitution  in  strong 
acids  and  alkalies,  and  l^vo-rotatory. 

Tests  for  Proteids.— 1.  With  Millon's  reagent  (mercury  dissolved  in 
its  own  weight  of  nitric  acid,  and  the  solution  diluted  with  twice  its 
volume  of  water)  a  precipitate,  rendered  red  by  boiling.  2.  Heated 
with  strong  nitric  acid,  they  become  yellow.  On  adding  ammonia  or 
caustic  soda,  or  potash,  the  yellow  is  replaced  by  an  orange  {xantho- 
proteic reaction).  3.  On  adding  caustic  alkali  and  a  drop  or  two  of 
copper  sulphate,  a  violet  color  is  produced,  which  can  be  deepened  by 
boiling.  4.  To  the  suspected  fluid  add  enough  acetic  acid  to  render  it 
decidedly  acid,  and  then  a  few  drops  of  potassium  ferrocyanide,  A 
white  precipitate  indicates  that  proteids  are  present.  5.  To  the  fluid 
rendered  decidedly  acid,  add  a  strong  solution  of  sodium  sulphate  and 
boil.     If  a  precipitate  falls,  some  proteid  was  present. 

The  first  three  tests  are  the  most  reliable,  and  apply  to  all  classes  of 
proteids. 

Propeeties  and  Classification  of  the  Proteids. 

I.  Native  Albumins. 

These  occur  naturally  in  the  tissues  and  fluids  of  the  body.  They 
are  soluble  in  water,  are  not  thrown  down  by  the  alkaline  carbonates, 
by  sodium  chloride,  or  by  very  dilute  acids.  Their  coagulation-point 
lies  below  70°  C.  They  may  be  dried  with  change  of  color  to  a  pale 
yellow,  but  remain  soluble. 

1.  Eo-g-AlbuDiin. — This  may  be  obtained  for  purposes  of  experiment 
by  cuttino-  up  raw  white  of  egg  with  scissors,  diluting  with  water,  strain- 
ing through  cotton,  and  afterward  through  filter-paper.  The  resulting 
fluid  is  almost  colorless  at  first,  but  on  standing  darkens  gradually.  It 
may  be  precipitated  by  strong  alcohol,  which  does  not  seem  to  alter 
its  chemical  constitution,  or  by  strong  acids,  when  a  great  chemical 
change  takes  place.  Various  mineral  salts,  as  silver  nitrate,  mercuric 
chloride,  etc.,  form  with  albumin  insoluble  compounds.  Whether  albu- 
min ever  exists  entirely  free  from  combination  with  salts  in  the  animal 
body  is  a  question ;  probably  not. 

By  the  addition  of  strong  acetic  acid  or  caustic  alkali,  a  clear,  jelly- 
like mass  results,  being,  in  the  first  case,  acid-albumin,  and  in  the  second 
alkali-albumin.     It  is  Isevo-rotatory  to  the  extent  of  35-5°  (—35-5°). 

2.  Serum-Albumin.— This  compound  greatly  resembles  the  foregoing, 
but  may  be  distinguished  by  the  following  characteristics :  (a)  Serum- 
albumin  is  not,  like  egg-albumin,  coagulated  by  ether.  (6)  Serum-albu- 
min is  less  readily  coagulated  by  strong  hydrochloric  acid,  and  any  pre- 
cipitate formed  is  easily  dissolved  by  excess  of  acid,  in  which  respects  it 
is  the  reverse  of  egg-albumin,  (c)  Coagulated  serum-albumin  is  readily 
soluble  in  strong  nitric  acid,  the  reverse  holding  for  egg-albumin,  (d) 
The  specific  rotation  of  egg-albumin  is  — 35*5°;  of  serum-albumin,  —56°. 
(e)  Serum-albumin  occurs  in  blood,  lymph,  chyle,  milk,  and  pathological 


APPEXDIX.  GT3 

transudations  ;  and,  when  injected  into  the  blood,  does  not  reappear  in 
the  urine,  while  the  injection  of  egg-albumin  is  followed  by  its  appear- 
ance in  the  urine  apparently  unaltered.  In  fact,  this  form  of  proteid 
constitutes  a  great  part  of  the  "  albumin  "  of  the  urme  of  such  signifi- 
cance in  pathological  conditions.  However,  increasing  knowledge  seems 
to  point  to  the  "  albiimiu  "  of  the  ui'ine,  like  many  other  forms  of  pro- 
teid, being  more  complex  than  was  once  supposed. 

II.  Derived  Albumins  (Albuminates). 

1.  Acid- Albumin. — This  may  be  formed  by  the  addition  of  a  strong 
acid  to  egg-albumin,  or,  more  gradually,  by  heating  a  weaker  solution 
of  egg-albumin  with  an  extremely  dilute  acid. 

Acid-albumin  is  characterized  by  non-precipitation  on  boiling,  com- 
plete precipitation  on  the  addition  of  a  dilute  alkali  to  the  point  of  neu- 
tralization— that  is,  acid-albumin  is  insoluble  in  water  or  such  like  neu- 
tral liquids.     It  is  soluble  in  an  excess  of  acid  or  of  alkali. 

By  treating  finely  minced  muscle  with  a  weak  acid,  a  substance  is 
obtained  not  readily  distinguishable  from  acid-albumin,  but  known  as 
syntonin.  This  is  probably  not  identical  with  acid-albumin  as  formed 
by  the  method  indicated  above,  though  a  distinguishing  test  of  a  wholly 
satisfactory  chai-acter  is  not  known.  Neither  this  substance  nor  acid- 
albumin  coagulates  on  boiling,  in  which  it  bears  a  resemblance  to  pep- 
tone. The  parapeptone  of  digestion  seems  to  be  very  similar  to  acid- 
albumin.  A  solution  of  acid-albumin  in  acid  may  be  precipitated  by 
the  addition  of  an  excess  of  common  salt. 

2.  Alkali-Albumin.— This  corresponds  to  the  foregoing,  and  may  be 
formed  in  a  similar  way  by  the  addition  of  an  alkali  instead  of  an  acid. 
It  is  not  coagulable  on  boiling,  and  is  precipitated  by  dilute  acid,  in 
excess  of  which  and  of  alkali  it  is  soluble,  but,  like  acid-albumin,  is  in- 
soluble in  water  and  solution  of  neutral  salts.  The  specific  rotation 
varies  with  the  mode  of  preparation,  from  which,  as  well  as  on  other 
grounds,  it  is  more  than  likely  that  there  are  different  kinds  of  alkali- 
albumin.  It  is  highly  probable  that  acid-albumin  and  alkali-albumin 
are  combinations  of  an  acid  or  an  alkali,  as  the  case  may  be,  with  albu- 
min, and  that  the  neutralization  precipitate  is  not  in  itself  either  one  or 
the  other. 

3.  Casein.— This  substance  is  the  proteid  most  characteristic  of  milk, 
from  which  it  may  be  obtained  by  dilution  ten  to  fifteen  times  with  water, 
adding  acetic  acid  till  a  precipitate  begins  to  form,  and  then  sending  a 
current  of  COs  through  the  fluid.  After  standing,  the  prccijjitate  may 
be  collected  in  a  filter.  It  is  freed  from  salts,  sxigar,  fat,  etc.,  by  first 
washing  with  water  and  then  with  alcohol  and  etlier. 

It  is  so  like  alkali-albumin  tbat  there  is  no  agreement  yet  as  to  the 
differences  between  them.  However,  the  presence  in  milk  of  potassium 
phospbate  modifies  tlie  reactions  of  casein  in  this  fluid.  It  may  be  precijn- 
tatcd  alsf)  by  axlding  magnesium  sulphat(i  to  saturation  to  milk.  This  pre- 
cipitate i.s,  however,  easily  solubh;  in  water.   Tlie  si)ecific  rotation  of  casein, 

when  in  solution  in  water  is  —SO'',  but  in  other  solutions  is  different, 
da 


674  ANIMAL   PHYSIOLOGY. 


III.  Globulins. 


This  class  of  bodies  is  characterized  by  being-  insoluble  in  water,  solu- 
ble in  dilute  saline  solutions  (especially  sodium  chloride)  ;  soluble  in 
dilute  acids  and  alkalies,  when  they  are  transformed  into  acid-albumin 
and  alkali-albumin  respectively.  Most  of  the  globulins  are  precipitated 
by  satiu'ation  with  solid  sodium  chloride. 

1.  Grlobulin  (Crystallin).— When  the  crystalline  lens  of  the  eye  is 
rubbed  up  with  fine  sand  and  extracted  with  water,  upon  filtration  and 
passing  a  stream  of  carbon  dioxide  through  the  filtrate,  a  precipitation 
of  globulin  is  obtained.  Though  strongly  resembling  paraglobulin  and 
fibrinogen,  it  is  not  known  to  favor  fibrin-formation. 

2.  Paraglobulin  (Fibrinoplastin).— This  body  may  be  obtained  from 
blood-serum  by  passing  through  it  a  current  of  carbonic  anhydride, 
when  a  flocculent  precipitate  falls,  which  later  becomes  very  finely  gran- 
ular, and  may  be  separated  by  filtration.  Addition  of  solid  sodium 
chloride  precipitates  this  substance  only  in  part.  It  is  very  readily 
changed  into  alkali-albumin,  and  still  more  so  to  acid-albumin,  by  addi- 
tion of  dilute  alkalies  or  acids.  This  body  is  not  easily  precipitated  by 
alcohol.     Its  coagulation-point  is  about  70°  C. 

Paraglobulin  has  been  found  in  blood-serum,  lymph,  chyle,  serous 
fluids,  the  aqueous  humor,  the  cornea,  connective  tissue,  and  in  the  pale 
and  colored  corpuscles.  It  occasionally  appears  in  urine  as  a  patho- 
logical product. 

3.  Fibrinogen. — While  greatly  resembliug  paraglobulin  in  most 
characteristics,  the  coagulation-point  is  different,  being  52°  to  55°  when 
in  solution  in  dilute  sodium  chloride.  It  is  not  so  readily  precipitated 
from  diluted  solutions  as  the  body  previously  described,  and  is  viscous 
rather  than  granular. 

It  may  be  obtained  from  blood-plasma  by  special  precautious,  though 
more  readily  from  hydrocele-fluid.  Fibrinogen  occurs  in  blood,  chyle^ 
serous  fluids,  and  numerous  trans^idations.  It  has  been  considered  by 
many  observers  to  be  essential  in  the  formation  of  fibrin. 

4.  Myosin,  as  its  name  implies,  is  derivable  from  muscle-plasma,  and 
may  be  regarded  as  the  latter  substance  in  an  altered  form.  It  may  be 
prepared  from  washed  muscle,  by  treatment  with  a  ten-per-cent  solution 
of  common  salt,  and  dropping  the  viscid  product  slowly  into  distilled 
water,  when  it  falls  as  a  flocculent,  whitish  precipitate.  It  is  readily  con- 
verted into  syntonin  (a  form  of  acid-albumin,  as  has  been  pointed  out) 
by  acids,  and  into  alkali-albumin  by  alkalies.  In  very  weak  acids  and 
alkalies  it  is  soluble  without  conversion  into  a  different  substance.  The 
coagulation-point  of  myosin  is  low,  55°  to  60°  C. 

5.  Vitellin.— This  body,  probably  united  with  lecithin,  is  the  chief 
proteid  constituent  of  the  yelk  of  egg,  from  which  it  is  usually  prepared. 
It  differs  from  most  of  the  globulins  in  not  being  precipitated  from  its 
solutions  by  sodium  chloride.  The  coagulation-point  lies  between  70° 
and  80°  C. 

6.  Grlobin  is  a  doubtful  member  of  this  class.     It  is  regarded  as  the 


APPENDIX.  675 

proteid  residue  of  liEemoglobiD.  It  is  uot  easily  soluble  in  dilute  acids 
or  sodium  chloride,  hence  it  is  with  hesitation  ranked  with  the  other 
globulins. 

IV.  Fibrin. 

This  body  has  peculiarities  which  warrant,  in  the  present  state  of  our 
knowledge,  its  separation  from  the  foregoing  and  placing  it  in  a  sepa- 
rate division.  It  is  insoluble  in  water  and  dilute  solutions  of  sodium 
chloride  ;  dissolved  only  with  difficulty  in  concentrated  neutral  saline 
solutions,  and  in  dilute  acids  and  alkalies. 

Fibrin  is  highly  elastic.  It  always  swells  under  the  action  of  weak 
(1  to  5  per  cent)  hydrochloric  acid.  But  continued  action  of  the  acid 
changes  the  fibrin  to  syntonin.  Heat  hastens  the  process.  By  the  ac- 
tion of  alkalies,  especially  when  aided  by  warming,  fibrin  is  converted 
into  alkali-albumin.  By  the  prolonged  action  of  solutions  of  sodium 
chloride  (10  per  cent),  sodium  sulphate,  etc.,  conversion  into  a  substance 
very  like  myo.sin  or  globulin  is  effected.  Myosin  may  be  regarded  as 
an  intermediate  product,  lying  between  globulin  and  fibrin.  This  be- 
comes clear  when  comparing  their  respective  solubilities  in  a  ten-per- 
cent solution  of  sodium  chloride.  Fibrin  and  myosin,  it  will  be  re- 
membered, are  both  the  products  of  coagulation  processes.  The  highly 
filamentous  character  of  fibrin  dLstiuguishes  it  physically  from  all  other 
proteids. 

Y.  Coagulated  Proteids. 

This  cla.ss  of  bodies  may  be  obtained  from  a  variety  of  others  by  the 
use  of  heat,  alcohol,  acids,  etc.  By  heating  to  about  70"  C.  solutions  of 
egg-albumin,  serum-albumin,  and  globulins  are  coagulated.  Precipi- 
tated acid-albumin  and  alkali-albumin,  and  fibrin  in  solution  in  salines, 
are  converted  into  coagulated  proteids  by  boiling.  The  digestive  juices 
act  readily  on  them,  converting  them  finally  into  peptones. 

VI.  Peptones. 

Peptones  are  proteids  which,  though  po.ssessing  little  absolute  difPu- 
sibility,  as  compared  with  solutions  of  ordinary  salts,  yet  pass  through 
animal  membranes  with  much  greater  readiness  than  any  other  proteids. 
ALso,  unlike  most  other  proteids,  they  are  not  coagulated  by  boiling. 
They  are  not  precipitated  by  cupric  sulphate,  ferric  chloride,  nor  usually 
by  potassium  fernjcyanide  and  acetic  acid.  Though  precipitated  by 
alcohol  from  .solution  in  water,  they  do  not  undergo  a  true  coagulation, 
even  after  standing  long  under  this  liquid. 

Peptones  are  coagulated  by  chlorine,  iodine,  tannin,  the  nitrates  of 
mercury  and  silver,  mercuric  chloride,  and  the  lead  acetates.  A  mere 
trace  of  cujji'ic  suljihatc  tf)  which  a  strong  solution  of  caustic  alkali  has 
been  add(;d,  iiitrodurtod  into  a  solution  of  peptones,  gives  rise  to  a  red 
(pink)  color.  If  more  than  a  trace  of  the  copper  salt  be  added,  the  usual 
proteid  reaction  results. 

Peptfmfis  may  be  formed  through  the  action  of  dilute  or  stronger 
acids  at  medium  torn pcratu res,  or  by  the  action  of  distilled  water  heated 


676  ANIMAL   PHYSIOLOGY. 

above  the  boiling-point  under  pressure  in  a  special  apparatus.  The  usual 
method  is,  however,  by  the  action  of  gastric  or  pancreatic  juice  on  white 
of  egg  or  other  form  of  proteid. 

It  seems  more  than  probable  that  the  bodies  formed  by  the  different 
methods  indicated  above  are  not  identical,  though  having  many  proper- 
ties in  coiTiBion.  Between  the  original  proteid  and  the  peptone  other 
bodies  seem  to  be  formed  either  as  by-products  or  as  intermediate  bod- 
ies, and  the  relation  of  these  has  been  expressed  in  tabular  form  (Foster) 
thus  : 

DecomjMsition  of  Proteids  by  Digestion. 

Albumin.  ^j- 

'S  i  ]  $1 

Si  I  1  ^ 

£   f  Antialbumose.  liemialbumose.  r~" 

I  I  I  ^^ 


.  i  I  I  I  I  S 

^   I  Antipeptone.         Antipeptone.  Heraipeptone.  Hemipeptone.     -^  -^ 


Leuein.    Tyrosin,      Leiicm.    Tyrosin, 

etc.  etc.  J  :^' 

Decompositio7i  hij  Acids. 

1. 

By  -25  per  cent  HCl  at  40°  C. 

Albumin. 

! 

I  I 

Antialbumate.     "  Hemialbumose. 


Antialbumid.  Hemi[ieptone.  Hemipeptone, 


By  3  to  5  per  cent  HoSO, 
Albumin. 

.at  100° 

C. 

Antialbumid. 
1 

1 
Hemialbumose. 

1 

Hemipeptone. 
.    Leuein,  Tyrosin,  etc. 

Hemipeptone. 
Leuein,  Tyrosin,  etc. 

It  will  be  observed  that  antialbumose  and  hemialbumose  are  inter- 
mediate products  of  digestion,  and  i\\Qj  occur  in  both  jjeptic  and  tryptic 
digestion. 

Antialbumate  takes  the  place  of  antialbumose  when  albumin  is  di- 
gested with  dilute  hydrochloric  acid  at  40°  C,  or  when  peptic  digestion 
is  not  normally  active.  It  can  be  changed  into  peptone  by  trypsin,  but 
not  by  pepsin,  and  seems  to  correspond  with  the  parapeptone  of  some 
authors  (Meissner).     The  table  is  also  meant  to  indicate  that  antialbu- 


APPENDIX.  077 

mose  and  heniialbumose  both  result  from  peptic  digestion,  and  it  is 
assumed  that  these  both  split  up  into  two  molecules  of  antipeptone  or 
hemipeptone,  accoi'ding  as  the  digestion  is  either  peptic  or  tryptic.  Evi- 
dently, trypsin  carries  the  processes  much  further  than  pepsin. 

VII.  Lardacein  (Amyloid  Substance). 

This  body  is  not  found  in  the  tissues  in  health,  but  results  from  a 
pathological  process,  and  is  most  frequently  found  in  the  sj)leen,  liver, 
kidneys,  lungs,  blood-vessels,  etc.  It  consists  of  CHNO  and  a  little  sul- 
phur in  some  oxidized  form.  It  is  insoluble  in  water,  dilute  acids  and 
alkalies,  and  neutral  saline  solutions.  Like  other  proteids,  it  can  be  con- 
verted into  acid-albumin  and  alkali-albumin ;  but,  unlike  all  other  pro- 
teids, it  is  not  affected  by  the  digestive  juices.  It  may  be  recognized  by 
giving  a  red  color  with  iodine,  and  a  violet  or  blue  when  heated  with 
iodine  and  sulphuric  acid. 

We  are  still  in  ignorance  of  the  real  molecular  constitution  of  pro- 
teids, and  our  whole  knowledge  of  this  class  of  bodies  is  in  the  empirical 
rather  than  the  scientific  stage. 

Nitrogenous  Non-crystalline  Bodies  allied  to  Proteids. 
These  bodies  resemble  each  other  much  less  than  the  proteids  jjroper  : 

1.  Mucin  (CHNO). 

It  is  the  characteristic  body  of  mucus,  which  abounds  in  the  bile  of 
the  gall-bladder  and  in  snails,  from  either  of  which  it  may  be  prepared. 
It  may  be  precipitated  from  its  solutions  by  alcohol,  alum,  mineral  acids, 
and  acetic  acid.  The  precipitate  is  dissolved  by  excess  of  mineral  acids, 
but  not  by  acetic  acid,  so  that  the  latter  forms  one  of  the  best  tests  for 
mucLii. 

2.  Chondrin  rCHNOS). 

This  substance  may  be  extracted  from  hj^aline  cartilage,  and  less 
easily  from  elastic  cartilage.  It  readily  gelatinizes  from  its  solutions  on 
.standing;  is  soluble  in  hot  water,  alkalies,  and  ammonia;  insoluble  in 
cold  water.  It  is  very  doubtful  whether  chondrin  of  itself  exists  in  car- 
tilage; it  is  more  likely  an  allied  product. 

3.  Gelatin,  or  Glutin  (CHNOS). 

This  substance  may  ]>e  obtained  by  heating"  connective  tissue  for  days 
with  dilute  acetic  acid  at  about  15°,  or  by  prolonged  treatment  with 
water  under  higli  pressures.  It  forms,  when  not  pure,  the  well-known 
"glue."  Though  swelling  in  cold  water,  it  does  not  dissolve,  but  is 
readily  soluble  in  warm  water.  It  forms  insoluble  precipitates  with  tan- 
nic acid  and  mercuric  chloride, 

4.  Elastln  rCHNO). 

This  is  one  of  the  most  insoluble  substances  derivable  from  animal 
tis.sues.  It,  however,  yields  to  concentrated  nitric  and  sulphuric  acids 
in  the  cf>ld  and  to  boiling  alkalies,  and  may  be  precipitated  from  its  solu- 
tions by  tannic  acid.  The  substance  is  best  obtained  from  the  liga- 
mentum  nucha?  of  the  ox. 


078  ANIMAL  PHYSIOLOGY. 

5.  Keratin  (CHNOS). 

It  makes  up  a  large  part  of  horn,  hair,  nails,  feathers,  and  is  also  a 
highly  insoluble  body.     In  all  probability  it  is  not  a  simple  substance. 

6.  Nuclein  (CHNOP). 

This  body  is  derivable  from  the  nuclei  of  cells,  from  yeast,  semen, 
and  from  the  yellow  corpuscles  of  the  yelk  of  eggs.  It  is  slightly  solu- 
ble in  water,  easily  so  in  alkalies,  though  the  solubility  changes  on  keep- 
ing. It  is  best  prepared  from  pus-corpuscles,  and  contains  a  notably 
large  quantity  of  phosphorus — nine  to  ten  per  cent. 

7.  Chitin  (CHNO). 

Though  not  occurring  in  appreciable  quantity,  at  all  events  in  the 
body  of  the  mammal,  it  makes  up  a  good  part  of  the  hard  covering  of 
insects,  crustaceans,  etc.  It  has  been  regarded  as  analogous  to  the  cellu- 
lose of  plants.  It  is  a  highly  insoluble  substance,  resisting  all  reagents 
except  strong  mineral  acids.  It  may  be  obtained  pure,  as  a  white  amor- 
phous body.  The  insolubihty  of  the  above  products  as  a  class  is  remark- " 
able.  Most  of  them  yield  either  leucin  or  tyrosin,  or  both,  under  hydro- 
lytic  treatment.  Their  relatious  are  very  ill  understood,  and  it  is  doubt- 
ful if  any  of  them  are  simple  substances,  or  exist  as  such  in  the  tissues 
frora  which  they  are  extracted  with  so  much  difficulty  in  most  instances. 
No  attempt  has  been  made  to  give  the  j)ercentage  composition  of  the 
above  bodies. 

Carbohydrates. 

Of  this  class  glycogen,  dextrose  (grape-sugar,  glucose),  maltose,  milk- 
sugar,  and  inosit  occur  normally  in  the  mammalian  body. 

The  exact  chemical  constitution  and  relations  of  the  sugars  are  still 
under  discussion  ;  we  shall,  therefore,  pass  this  subject  over  in  this  brief 
outline. 

1.  Dextrose  (grape-sugar).     CeHioOs. 

The  occurrence  of  this  body  in  the  various  fluids  and  tissues  has  been 
already  considered. 

This  sugar  crystallizes  fi'om  aqueous  solutions  in  prisms,  which  may 
be  agglutinated  into  lumps,  and  is,  when  chemically  pure,  colorless, 
readily  soluble  in  warm  water,  more  slowly  soluble  in  cold  water,  spar- 
ingly soluble  in  alcohol,  and  insoluble  in  ether.  Specific  rotation, 
-I-  104° — i.  e.,  dextro-rotatory  104°  for  yellow  light.  In  the  presence  of 
yeast-cells,  and  at  a  temperature  of  from  5°  to  45°  0.  (best  at  about  25°  C), 
dextrose  undergoes  the  alcoholic  fermentation.  The  reactions  may  be 
thus  expressed: 

CsHi^Oe  =  2C2H6.OH  +  2CO2. 

In  the  presence  of  decomposing  nitrogenous  matter,  as  the  casein  of 
milk,  the  lactic  fermentation  results. 

Reactions : 

(a)  CeHi.Oe  =  2C3H6O3. 

Lactic  acid: 

(b)  2C3Ha03  =  C4H8O2  -f-  2CO2  -I-  3H2. 

Butyric  acid. 


APPENDIX.  G79 

A  temperature  of  about  35°  C.  is  the  most  fayorable  for  this  fermen- 
tation. Dextrose  readily  I'educes  copper  salts  in  the  presence  of  caustic 
alkali. 

Maltose.    C12H32O11. 

This  sugar  may  be  artificially  produced  by  the  action  of  diastase,  a 
fei'ment  obtained  from  malted  barley,  on  starch. 

SCeHioOs  +  H.O  =  Ci^H.-.On  +  CeH.oOs. 

Starch.  Maltose.  De.\'tnu. 

It  may  also  be  foi'med  by  the  action  of  dilute  sulphuric  acid  on 
starch.  It  reduces  copper  salts ;  is  dextro-rotatory ;  ferments  with  yeast, 
and  crystallizes  in  fine  needles.  It  seems  to  be  the  principal  sugar 
formed  in  the  natural  digestive  processes. 

Milk-Sugar  (lactose).    CiaHaoOu. 

This  form  of  sugar  is  found  in  the  milk  of  all  animals  normally,  and 
occasionally  in  the  urine  of  animals  during  lactation. 

It  crystallizes  in  rhombic  prisms  ;  its  taste  is  slightly  sweetish;  is 
dextro-rotatory  ;  much  less  soluble  in  water  than  cane-sugar.  When 
the  lactose  of  milk  ferments ;  it  breaks  up  into  alcohol  and  lactic  acid, 
hence  the  souring  of  milk.  It  reduces  solutions  of  copper  salts,  but  less 
perfectly  than  dextrose,  and  is  dextro-rotatory. 

InOSit.      CeHiaOe. 

This  substance  has  been  obtained  sparingly  from  the  muscle-cells  of 
the  heart  and  from  some  other  organs.  It  crystallizes  in  rhombic 
prisms ;  readily  soluble  in  water  but  insoluble  in  alcohol  and  ether.  This 
sugar  has  no  specific  action  on  light,  and  is  susceptible  of  the  lactic  fer- 
mentation. 

Dextrin.    CeHioOs. 

This  substance  may  be  formed  by  the  action  of  dilute  acids  on  starch, 
or  by  the  action  of  diastase  on  the  same  body.  It  is  strongly  dextro- 
rotatory, does  not  reduce  solutions  of  copper  salts,  gives  a  red  color 
with  iodine,  is  soluble  in  water,  and  precipitated  by  alcohol.  It  is  a 
product  of  both  artificial  and  natui'al  digestion. 

By  the  action  of  acids  and  ferments  on  starch,  certain  modifications 
of  dextrin  are  formed.  Of  these,  erythrodextrin  becomes  sugar  by  the 
continued  action  of  ferments.  Achroodextrin  remains  unaltered  and  is 
characterized  by  giving  no  red  color  with  iodine.  It  may  be  converted 
into  dextrose  by  boiling  with  dilute  hydrochloric  acid. 

Glycogen.    CoHioOs. 

This  substance  is  pretty  widely  distributed  in  the  organs  of  the  body 
especially  in  the  mammalian  foetus,  and  is  found  in  abundance  in  the 
liver  of  the  adult  in  both  vertebrates  and  invertebrates.  Glycogen  when 
pure  is  wliite,  amorphous,  ta,steless,  easily  soluble  in  water,  insoluble  in 
alcohol  and  ether,  highly  d<;xtro-rot'itory,  and  does  not  i-oduce  metallic 
oxides.  It  is  changed  by  the,  digestive  ferments  into  a  form  of  sugar 
and  of  dextrin,  and  giv(!s  a  red  Cport-wine)  color  with  iodine,  which  dis- 
appears on  warming  l;ut  returas  on  cocding,  by  which  latter  it  is  distin- 


6S0  ANIMAL   PHYSIOLOGY. 

guislied  from  dextrin.  It  is  "best  extracted  from  the  liver,  removed  as 
soon  as  possible  after  killing  an  animal  and  minced,  by  boiling  water, 
then  purified  and  precipitated. 

Tunicin.    C6H10O6. 

This  body  is  closely  allied  to  the  cellulose  of  plants,  and  forms  the 
greater  part  of  the  integument  of  ascidians  or  tunicates.  Like  chitin,  it  is 
extremely  insoluble. 

Fats,  Fatty  Acids,  eto. 

G-eneral  formula  of  series  :  CoHonOa  or  GJl^^+i.GOJl. 

The  fatty  acid  series  answei-s  to  the  series  of  monatomic  alcohols: 
thus,  formic  acid  corresponds  to  methyl  alcohol,  and  acetic  acid  to  ethyl 
or  ordinary  alcohol. 

C^HoO  +  02  =  C2H4O2  +  H2O,  or 
C.H5.OH  +  O2  =  CH3.CO.OH  +  H2O. 

From  which  it  appears  that  O  has  taken  the  place  of  H2  in  the  alco- 
hol to  form  the  acid — i.  e.,  the  acid  is  an  oxidized  alcohol.  The  lowest 
members  of  the  line  are  volatile  liquids  with  strongly  acid  reactions. 
As  the  series  is  ascended,  fluidity  diminishes,  and  finally  the  acids  are 
solids,  greatly  resembling  the  neutral  fats  in  appearance. 

The  derivatives  of  the  fatty  acids  are  very  important  in  the  animal 
economy,  but  the  free  acids  occur  sparingly. 

Formic  acid.    H.CO2H. 

A  strongly  corrosive  liquid,  boiling  at  100°  C,  solidifying  at  0°,  and 
mixing  readily  with  water  and  alcohol.  It  has  been  extracted  from 
various  organs. 

Acetic  acid.    CH3.CO2H. 

An  acid  liquid  of  characteristic  odor,  boiling  at  117°  C,  solidifying  at 
5°  C.     Readily  miscible  with  alcohol  and  water. 

It  often  occurs  in  the  stomach,  from  fermentative  changes. 

Propionic  acid.    C2H6.CO2H. 

Eesembles  acetic  acid,  soluble  in  water  and  boiling  at  141°  C.  It 
is  found  in  perspiration,  the  stomach,  diabetic  urine  when  ferment- 
ing, etc. 

Butyric  acid.    C3H7.CO2H. 

An  oily,  colorless  liquid,  with  the  smell  of  rancid  butter,  soluble  in 
water,  alcohol,  ether  ;  and  boiling  at  162°  C. 

It  is  found  in  sweat,  faeces,  urine,  and  the  contents  of  the  large  in- 
testine. 

Valerianic  acid.    C4H9.CO2H. 

An  oily  liquid  of  strong  smell  and  taste,  soluble  in  water,  and  more 
so  in  alcohol  and  ether.  It  is  found  in  solid  excrement.  In  fatty  de- 
generation of  the  liver  it  may  occur  in  the  urine,  as  a  result  of  the 
decomposition  of  leucin,  which  appears  in  abundance  in  the  urine  in 
the  above  disease. 


APPENDIX.  6S1 

Caproic  acid.      CsHn.COaH. 

Caprylic  acid.    CMIis.COiH. 

Capric  acid.        CsHig.COaH. 

These  acids  enter  into  the  fats  of  butter,  from  which  they  are  readily 
prepared.  They  are  all  soluble  to  but  a  slight  extent  in  water,  but 
readily  in  alcohol  and  ether.  They  probably  occur  in  the  products  of 
the  sebaceous  glands  and  the  sweat,  at  least  occasionally  in  some  ani- 
mals. 

Laurostearic  acid.    CnHaa.COaH. 
Myristic  acid.  CisH^t.COsH. 

They  occur  as  neutral  fats  in  butter,  spermaceti,  etc. 

Palmitic  acid,    C15H31.CO2H. 

Stearic  acid.       CnHas.COsH. 

These  are  colorless  solids  with  melting-points,  the  former  at  G2°  C, 
the  latter  at  09 '2''  C.  Insoluble  in  water,  but  readily  dissolved  by  hot 
alcohol,  ether,  or  chloroform.  With  alkalies  they  form  soaps;  and  with 
glycerin  they,  together  with  the  oleates,  make  up  the  greater  part  of 
human  fat.  As  salts  of  sodium  (?)  they  occur  in  chyle,  blood,  serous 
fluids.  Combined  with  calcium  they  occur  in  the  faeces  and  the  adipo- 
cere  of  the  buried  cadaver.  They  ai'e  said  to  occur /ree  in  the  caseous 
nodules  of  tubercle  and  in  decomposing  pus. 

The  Oleic  (Acrylic)  Acid  Series. 

General  formula  of  series  C„H2„_20>  Several  of  the  acids  of  this 
series  occur  as  compounds  of  glycerin  ivi  various  fats.  They  may  be 
decomposed  into  acids  of  the  acetic  series. 

Oleic  acid.     CiJIa.Oa. 

The  most,  important  to  the  physiologist;  is  a  colorless,  oily  liquid 
solidifying  to  a  crystalline  mass  at  4°  C.  Soluble  in  alcohol  and  ether 
but  not  in  water  ;  forms  soaps  with  alkalies. 

The  Neutral  Fats. 

To  understand  this  class  of  bodies  it  becomes  necessary  to  bear  in 
mind  the  relations  of  the  acids  of  the  fatty  and  oleic  series  to  glycerin. 
Glycerin  may  be  regarded  as  a  tri-acid  alcohol: 

C  OH      HO.OC.C>5H3,  (  O.CO.C.r.H„ 

C,H6  \  OH  +  HO.OC.C.oHa,  =  C3H5  ]  O.CO.CisH,.  +  3H.0. 
(oh      HO.OC.C.0H3.  (O.CO.CuH,! 

Glycerin.  Palmitic  acid.  filyceriri  tri-palmitatu  or  palmitin. 

From  which  the  relations  of  glycerin  and  a  fatty  acid  to  the  neutral  fat 
appear — i.  e.,  a  neutral  fat  is  the  result  of  the  replacement  of  the  ex- 
cliangoable  atoms  of  liydrogon  in  the  tri-atomic  alcohol  (glycerin)  by 
the  acid  radicles  of  the  acetic  f)r  oleic  series  ;  so  tliat  the  neutral  fats  may 
be  regai'ded  as  ethers,  of  which,  in  tlie  nature  of  the  ca.se,  there  are  theo- 
retically three  ;  but  those  only  in  which  the  most  complete  snl)stitution 
has  taken  place  are  of  importance  from  a  physiological  point  of  view. 


(582  ANIMAL   PHYSIOLOGY. 

These  neutral  fats  are  insoluble  in  water  and  cold  alcohol,  soluble  in  hot 
alcohol,  ether,  chloroform,  etc. 

By  the  action  of  caustic  alkalies  or  si;perheated  steam  they  may  be 
readily  decomposed  into  glycerin  and  their  fatty  acids. 

Saponification  may  be  thus  represented  : 

(  O.OC.CiaHai 

CH3  {  O.OC.C15H31  +  3K0H  =  C3H6(OH)3  +  3C:5Hsi.C02K:. 
(O.OC.C15H31 

Palinitin.  Glycerin.  Potassium  palmitate. 

It  is  known  that  fats  are  not  only  emulsified  in  the  alimentary  tract, 
but  split  up  into  their  component  fatty  acids  and  glycerin.  A  certain 
proportion  of  soluble  soaps  are  formed  and  taken  into  the  blood  ;  some 
insoluble  soaps  appear  in  the  faeces. 

But  the  chemical  changes  of  fats,  destructiye  and  constructive,  effect- 
ed by  the  organs  that  prepare  food  to  become  blood,  are  doubtless  very 
complex,  and  in  large  part  as  yet  unknown. 

GlycoUc  Acid  Series. 

Glycol  may  be  formulated  thus  :    1     '       ,  the  general  formula  of  the 

glycols  being  CnHo^+^Oa— i.  e.,  the  glycols  are  diatomic  alcohols,  from 
which  acids  may  be  obtained  by  oxidation,  thus  : 

CH.OH      ^      CO.H 

6h.oh  +  ^  =  ch.oh  +  ^^^- 

Glycol.  Glycolic  acid. 

By  additional  oxidation  a  member  of  the  glycolic  series  may  be  con- 
verted into  one  of  the  oxalic  series,  thus  : 

V^'        +0.  =  (C0.H)2  +  H=0. 
CH2OH 

Glycolic  acid.  Oxalic  acid. 

/OTT 
1.  Lactic  acid.   CsHeOs  or  C2H4  ^qqsH' 

Exists  in  four  isomeric  conditions,  three  of  which  have  been  found  in 
the  mammalian  (human)  body.  These  have  the  following  properties  in 
common  :  Are  sirup-like  in  consistence,  colorless,  soluble  in  water,  alco- 
hol, and  ether  ;  have  an  extremely  sour  taste  and  a  strong  acid  reaction. 
They  form  salts  (lactates)  with  the  metals,     (a)  Ordinary  lactic  acid,  in 

active  ethylidene-lactic  acid,  a  hydroxyl-propionic  acid,  CHs.CH^qqJjj^ 
This  is  the  form  of  lactic  acid  that  occurs  in  the  fermentation  of  milk. 
It  is  found  in  the  contents  of  the  stomach,  intestines,  and  pathologically 
in  the  urine,  (b)  Ethylene-lactic  acid.  This  isomer  of  lactic  acid 
occurs,  though  there  is  some  doubt  about  the  subject,  in  muscle,     (c) 

/OTT 
Sarcolactic  acid,  active  ethylidene-lactic  acid,  CHs.CH^qq^jj.     This 

acid  maybe  readily  obtained  from  flesh,  and  is  therefore  found  in  abun- 
dance in  the  "meat  extracts."     It  is  the   only  one  of  the  lactic  acids 


APPEXDIX.  683 

that  rotates  the  plane  of  polarized  light,  the  free  acid  being  dextro-ro- 
tatory. 

The  Bibasic  Acids  (C„H2„_20o)  of  the  Oxalic  Series. 

Only  a  few  membei's  of  this  series  are  of  special  interest  to  the  medi- 
cal chemist. 

Oxalic  acid.    C2Ho04,(C02H)2. 

Does  not  occur  free  in  the  mammalian  body,  but  is  normally  present 
in  small  quantity  as  an  oxalate,  chiefly  of  calcium,  in  the  urine  of  most 
mammals.  In  certain  disordered  states  of  the  metabolism  it  occurs  in 
the  urine  of  man  in  characteristic  dumb-bell  forms,  in  regular  octahedi'a, 
or  in  square  columns  with  pyramidal  ends.  These  are  insoluble  in 
water,  alcohol,  ether,  ammonia,  and  acetic  acid,  but  readily  dissolve  in 
hydrochloric  acid. 

Succinic  acid.    CiB.i(COiH)i. 

Occurs  in  the  spleen,  thymus  and  thyroid  bodies,  and  in  hydrocele 
and  hydrocephalic  fluids.  It  crystallizes  in  large  rhombic  tablets,  and 
more  rarely  in  jDrisms ;  sparingly  soluble  in  water. 

Complex  Nitrogenous  Fats. 

The  bodies  to  be  described  in  this  chapter  may  most  of  them  be  ex- 
tracted from  the  nerves  and  nervous  centers. 

Lecithin.    C44H90NPO9. 

This  substance  may  be  obtained  from  diverse  sources— thie  blood,  bile, 
serous  fluids,  and  especially  from  the  brain,  nerves,  yelk  of  egg,  semen, 
pus,  the  colorless  corpuscles,  and  even  the  electrical  organ  of  fishes.  It 
may  be  separated  as  a  white,  somewhat  crystalline,  soft  body,  soluble  in 
cold  alcohol,  more  so  in  hot  alcohol,  in  ether,  chloroform,  fats,  benzol, 
etc. 

Glycerinphosphoric  acid.    CsHaPOe. 

May  arise  as  a  decompo.sition  product  of  lecithin,  thus : 

a^Hs.NPO.  +  3H,0  =  2C.eH3602  +  CaHaPO,  +  CsH.oNOs. 

Lecithin.  Stearic  acid.      Glj-ceriii  phos-  Neuriu. 

phoric  acid. 

Protagon.    C1.0H30.N5PO35  (?). 

Thfi  formula  of  most  of  these  bodies  is  doubtful,  and  especially  is  this 
remark  true  of  protagon.  This  body  is  insoluble  in  cold  water,  but 
swells  in  it  like  gelatin.  At  200°  C.  it  melts  to  a  sirup.  There  has 
been  much  di.scussion  as  to  whether  it  is  a  single  body,  or  a  mixture  of 
lecithin  and  cerclnuu.     It  is  derivable  from  the  brains  of  mammals. 

Neurin.    CsH.gNOk. 

It  is  a  very  unstable  body,  difficult  to  get  or  keep  in  a  free  state.  It 
has  boon  obtained  from  bile;  hence  the  name  cholin. 

Cerebrin.    CnHajNOs  (?). 

Abounds  in  the  brain  in  the  axis  cylinder  of  nerves  and  in  pus-cor- 
puscles.    It  may  Ix;  obtained  as  a  colorless  hygroscopic  powder. 


684  ANIMAL  PHYSIOLOGY. 

The  Series  of  Bile  Acids,  etc. 

Cholie  (cholalic)  acid.     C24H40O6. 

It  is  the  starting-point  of  the  bile-acid  series,  and  may  be  obtained 
pure  in  an  amorphous  or  crystalline  form,  soluble  in  water.  This  acid 
is  dextro-rotatory.  It  may  occur  in  the  large  or  small  intestine  and  in 
the  faeces.  In  jaundice  it  is  in  excess  in  the  blood,  tissues,  and  excre- 
tions, especially  the  urine. 

Pette7iJcofer's  Tes^.— With  sugar  and  sulphuric  acid  it  gives  a  red- 
dish color,  which  may  or  may  not  require  slight  heat  for  its  production ; 
but  it  is  important  to  remember  that  this  reaction  may  be  produced  by 
other  substances,  so  that  the  test  is  at  best  by  itself  a  doubtful  one. 

Glycocholic  acid.    C26H43NO6. 

This  is  the  principal  acid  of  ox-gall ;  occurs  also  in  that  of  man,  but 
apparently  not  in  the  bile  of  cai'nivora. 

This  acid  crystallizes  in  fine  needles,  soluble  in  water  especially  if 
hot,  in  alcohol,  but  not  in  ether.     It  has  a  strongly  acid  reaction. 

C=4H40O5  f         C2NH6O2         -         H2O         =         C26H43NO6. 

Cholalic  acid.  Glycin.  Glycocholic  acid. 

Whether  it  is  formed  in  the  body  in  the  manner  indicated  by  the 
above  equation  is  uncertain,  as  glycin  has  not  as  yet  been  obtained  free 
from  any  tissue.     This  acid  is  best  prepared  from  ox-gall, 

Taurocholie  acid.    C26II46NSO7. 

Though  found  in  ox-gall  it  is  most  plentiful  in  human  bile,  that  of  the 
carnivora,  and  especially  in  dog's  gall. 

It  crystallizes  in  needles  but  not  readily.  It  is  soluble  in  water  and 
alcohol,  insoluble  in  ether.  Its  salts  are  also  soluble  in  water.  Tauro- 
cholie acid  is  a  very  insoluble  substance. 

C26H45NO7S  =  C24H40O5  +  C2H,N03S  -  H2O. 

Taurocholie  acid.     Cholalic  acid.  Taurin. 

Like  the  preceding,  it  is  dextro-rotatory. 

Cholesterin.    C26H43.OH. 

Eemarkable  as  the  only  free  alcohol  occurring  in  the  human  body. 
This  substance  may  readily  and  in  great  abundance  be  extracted  from 
the  nervous  tissues,  but  most  easily  from  gall-stones,  of  which  it  forms  a 
large  part.  It  can  be  derived  from  other  tissues,  the  blood  and  especial- 
ly bile.  It  may  be  obtained  in  white  fine  needles  from  solution  in  hot 
alcohol,  ether,  etc.     The  substance  is  Igevo-rotatory. 

Test. — Strong  sulphuric  acid  added  to  it  in  solid  form  and  heated,  or 
to  its  solution  in  chloroform,  gives  a  bright-red  color,  which  changes  on 
standing. 

Bile-Pigments. 

Bilirubin.     CigHisNsOs. 

It  makes  up  a  great  part  of  the  pigment  of  the  bile  of  the  carnivora 
and  perhaps  of  man.  It  abounds  also  in  gall-stones,  from  which  it  may 
be  obtained,  in  either  the  amorphous  or  crystalline  condition,  by  extract- 
ing with  chloroform  and  further  treatment.     When  heated  with  nitrous 


APPENDIX.  G85 

acid  it  undergoes  a  series  of  oxidations,  giving  rise  to  distinct  prodvicts 
of  which  one  is  the  green  biliverdin.  These  oxidations  are  the  basis  of 
Gmelin''s  test  for  bile-pigment,  which  consists  in  adding  a  drop  of  strong 
nitric  acid  containing  nitrous  acid  to  bile,  when  a  series  of  rather  rai)id 
changes  in  color  in  a  certain  order  takes  place. 

Biliverdin.     C.eH.sN^O*. 

It  is  this  pigment  which  gives  the  characteristic  color  to  ox-gall,  from 
which  it  is  best  prepared.  It  is  not  soluble  in  ether  or  chloroform,  but 
dissolves  readily  in  alcohol. 

In  all  probability  both  the  bile-pigments  and  their  derivatives  are 
the  result  of  the  final  transformations  of  ha^mogloliin. 

Choletelin.     CisHisN^Os. 

This  is  the  fhial  product  of  the  oxidation  of  bilirubin. 

Hydrobilirubin.    C32H40N4O7. 

When  an  alkaline  solution  of  bilirubin  is  acted  upon  by  sodium  amal- 
gam, the  above  results.  It  is  thought  by  many  to  be  identical  with  ster- 
cobilin,  a  product  of  the  decomposition,  etc.,  of  bile  in  the  intestine.  Since 
hydrogen  in  the  nascent  condition  probably  occurs  in  the  intestines  as 
the  result  of  fermentations,  the  conditions  for  the  formation  of  this  sub- 
stance seem  to  be  met. 

Pigments  of  Urine. 

It  seems  to  be  more  than  probable  that  the  urine  contains  a  great 
number  of  pigments.     But  few  of  these,  however,  have  been  isolated. 
The  best  known  are  the  following: 

Urobilin.    C32H40N4O7. 

The  formulae  of  all  these  bodies  are  but  indifferently  known. 
Urobilin  is  thought  to  be  identical  with  hydrobilirubin.     It  is  pres- 
ent, but  in  small  quantities,  in  normal  urine,  though  often  largely  in  the 
urine  of  febrile  conditions.     It  is  supposed  to  be  an  oxidi.^ed  form  of 
chromogen. 

Uroerythrin. 

Sui)posed  to  abound  in  the  urine  of  rheumatic  patients.  It  becomes 
greenish  on  addition  of  caustic  alkali,  and  reddish  or  reddish-yellow  when 
concentrated  hydrochloric  acid  is  added. 

The  Indigo  Series. 

Indican.    CzoHsiNO.a. 

Borne  regard  indican  a.s  indoxyl  sulphuric  acid,  which  does  not  occur 
in  the  free  state,  but  as  a  salt  of  potassium.  It  represents  in  the  urine 
the  indol  of  tlie  alimentary  canal. 

Indigo.     Ci.H.oNsOa. 

It  occasionally  occurs  in  sweat  and  urine  as  an  oxidation  product  of 
indican. 

It  may  bo  obtained  froin  human  urine,  and  still  more  readily  from 
that  of  the  hcrbivora.  I)y  tin;  cautions  jiddilion  of  a  weak  solution  of 


686  ANIMAL  PHYSIOLOGY. 

chlorinated  lime  to  some  urine  to  wliich.  an  equal  bulk  of  strong  hydro- 
cMoric  acid  has  been  added.  Unless  great  care  is  employed  in  mixing 
up  the  fluids,  in  the  drop-by-drop  addition  of  the  solution  of  chlorinated 
lime,  the  indigo-blue  will  be  oxidized  (bleached)  to  indigo-white. 

The  substance  is  soluble  in  chloroform  which,  being  heavy,  falls  to 
the  bottom  of  the  glass  and  carries  with  it  the  indigo. 

Indol.     CsHtN. 

A  substance  to  which  the  odor  of  faeces  is  in  part  due.  It  occurs  in 
artificial  and  natural  pancreatic  digestion  as  a  product  of  the  action  of 
bacteria.  It  is  crystalline,  soluble  in  boiling  water,  alcohol,  and  ethei'. 
Its  alcoholic  solution  when  nitrous  acid  is  added  gives  a  red  color  and 
its  aqueous  solution  a  red  precipitate. 

Skatol.     C9H9N  (?). 

A  substance  occuming  under  the  same  circumstances  as  indol.  It 
does  not  give  the  same  reactions  with  nitrous  acid  as  indol,  but  gives  a 
violet-red  color,  when  in  urine,  on  the  addition  of  concentrated  hydro- 
chloric acid.  It  may,  like  the  preceding,  be  obtained  in  crystalline 
form. 

Nitrogenous  Metabolites. 

As  may  be  gathered  by  a  perusal  of  the  chapter  on  the  metabolism 
of  the  body,  the  nitrogenous  metabolism,  while  most  interesting  and 
important,  presents  jDroblems  which  as  yet  are  in  great  part  unsolved. 
However,  something  more  of  the  nature  of  certain  nitrogenous  chemical 
compounds,  either  occurring  in  the  body  or  related  to  such  as  are  present, 
may  now  be  considered  with  advantage. 

Urea.    C0;^^^ 

Urea  may  be  regarded  as  the  most  important  and  by  far  the  most 
abundant  solid  of  the  urine  of  man  and  many  other  mammals,  includ- 
ing practically,  so  far  as  known,  all  the  carnivora  and  several  other 
groups.  It  also  occurs  to  a  slight  extent  in  the  urine  of  birds.  It  is 
found  in  small  quantity  in  blood  and  many  of  the  fluids  of  the  mam- 
malian body,  though  not  at  all  or  to  but  the  smallest  extent  in  muscles. 
It  may  be  prepared  from  urine  and  obtained  in  colorless  needles,  soluble 
in  water  and  alcohol,  but  not  in  anhydrous  ether.  When  urine  decom- 
poses, urea,  possibly  under  the  action  of  a  ferment,  becomes  ammonium 
carbonate :  ^-pr 

CO(^g^  +  H.O  =  (NH3)2C03. 

Urea  may  be  made  in  the  laboratory  in  several  ways,  some  of  which  are 
indicated  in  the  following  equations : 

1.  By  heating  ammonium  carbonate : 

^^(0NH4  =  CON.H4  +  H.O. 

2.  By  heating  ethyl  carbonate  with  ammonia: 

^^CocIhI  +  2^^'  =  CON2H4  +  2C2H6O. 


APPENDIX.  087 

3.  By  addition  of  water  to  cyan-amide : 

CN.NHa  +  H,0  =  CON2H4. 

4.  By  evaporation  of  ammonium  cyanate  in  aqueous  solution  : 

CN(0NH4)  =  CON2H4. 

The  last  reaction  possesses  a  historical  interest,  for  it  was  by  this 
method  that  an  organic  compound  occurring-  in  the  animal  body  was 
first  formed  from  inorganic  substances  in  the  laboratory  by  Wohler  in 
1828.  Urea  forms  compounds  with  acids,  the  most  interesting  of  which 
to  the  student  of  animal  chemistry  is  the  following : 

Urea  nitrate.    CH4Nc,O.HN03. 

When  luune  is  concentrated,  and  strong  nitric  acid  added  cautiously, 
the  above  crystallizes  out  in  glistening  six-sided  or  rhombic  tablets,  solu- 
ble in  water,  but  insoluble  in  ether.  This  makes  a  reliable  and  fairly 
delicate  test  for  the  presence  of  urea. 

TJric  acid.    CBH4N4O3. 

This  metabolite  occurs  in  the  spleen  and  several  other  organs  and 
tissues;  sparingly  in  the  urine  of  man  and  most  mammals;  abundantly 
in  that  of  birds  and  serpents,  in  which  it  takes  the  place  of  ui'ea.  In  its 
Ijurest  form  it  presents  itself  as  a  colorless  crystalline  powder,  tasteless 
and  odorless.  Its  crystalline  forms,  arising  spontaneously  from  urine, 
are  very  variable  and  always  colored.  Very  insoluble  in  cold  water, 
ether,  and  alcohol ;  readily  soluble  in  sulphuric  acid,  caustic  alkalies, 
and  some  of  their  salts.  The  most  important  salts  of  uric  acid  are  the 
urates  of  sodium,  potassium,  and  ammonium,  all  of  which  occur  in  urin- 
ary sediments. 

The  murexid  test  for  uric  acid  is  as  follows:  Add  strong  nitric  acid 
in  very  small  quantity,  and  evaporate  to  dryness,  when  a  red  color 
should  appear,  which  on  addition  of  ammonia  gives  rise  to  a  purple. 
The  following  equations  will  show  the  relations  of  uric  acid  to  lu'ea,  etc., 
so  far  as  laboratory  reactions  are  concerned.  We  have  in  the  body  of 
the  work  sliovvn  that  ui'ic  acid  is  not  in  all  probability  itself  an  anteced- 
ent of  urea  in  the  body: 

C6II4N403    +    H.O    -f    O    =   C4H.N2O4    -t-    CN2H4O. 

Uric  acid.  Alloxan.  Urea. 

C4N,H.04  -I-  2H2O  =  CHaOs  -f  CN  Ji40. 

AUcjxan.  Mesoxalic  acid.       Urea. 

C6H4N4O3  +  H,0  +  O  =  C4H„N403  +  CO,. 

Uric  acid.  Allautuin. 

C4H.N4O3  +  H.O  =  CH4N,0  -f-  C3H4N,0. 

Allantoin.  Urea.  Allantnric  acid. 

Uric  acid  h;is  been  made  artificially  by  fusing  together  urea  and  glyco- 
cin  (glycin,  glycocoll,  or  amido-acetic  acid) : 

*""'  CO,H- 
Creatin.    C4H.N3O,. 

This  body  may  be  abstracted  from  dead  muscle,  and  obtained  either 
in  a  white  amorphous  condition  or  in  rhojnl)ic  prisms,  soluble  in  cold 


68S  ANIMAL   PHYSIOLOGY. 

water  and  in  ether;  less  so  in  alcohoL  Creatin  maybe  changed  into 
urea  and  sarcosin  or  methyl-glycin : 

C4H9N3O2  +  H2O  =  C3H7NO2  +  CON2H4. 

Creatin.  Sarcosin.  Urea. 

It  may  also  be  formed  synthetically  under  the  action  of  acids.  Creatin 
may  by  dehydration  be  transformed  into  creatin  in. 

Creatinin.    C4H,N30. 

This  body  may  be  regarded  as  dehydrated  creatin.  It  occurs  nor- 
mally in  flesh  and  urine,  and  may  be  obtained  in  prisms;  soluble  in 
water  and  alcohol,  but  not  appreciably  in  ether.  It  acts  as  a  strong 
base,  the  most  important  salt  being  the  zinc  chloride  (C4ll7N30)2ZnCl2. 

Allantoin.    CiHeNiOa. 

A  body  characteristic  of  the  allantoic  fluid  of  foetal  life,  and  which 
may  occur  in  the  urine.  Its  relations  to  viric  acid  and  urea  have  been 
indicated  above. 

Hypoxanthin  (sarkin).     C5II4N4O. 

Occurs  in  flesh,  in  the  spleen,  liver,  medulla  of  the  bones,  etc.  It 
may  be  obtained  in  fine  needles,  soluble  in  hot  water. 

Xanthin.    C5H4N4O2. 

May  be  derived  from  muscles,  the  liver,  spleen,  thymus,  and  some 
other  organs  and  tissues.  It  is  probably  a  normal  constituent  of  the 
iirine  in  minute  quantity.  It  may  be  obtained  as  a  colorless  powder, 
only  slightly  soluble  in  water,  but  soluble  in  dilute  acids  and  alkalies. 
Xanthin  may  be  regarded  as  the  oxidized  form  of  hypoxanthin. 

Carnin.     C7HeN403. 

Occurs  in  extract  of  flesh,  and  may  be  obtained  in  crystals,  insoKible 
in  alcohol  and  ether,  but  slightly  soluble  in  cold  water,  and  more  so  in 
hot  water.  , 

Guanin.    CsHoNeO. 

So  called  because  first  obtained  from  guano  (excrement  of  birds) ;  it 
is.  however,  also  to  be  extracted  from  several  organs  and  tissues ;  as  a 
white  amorphous  powder,  insoluble  in  water,  alcohol, ,  ether,  etc.  By 
treatment  with  nitrous  acid  it  may  be  converted  into  ;£:anthin. 

Kynurenic  acid.    C20H14N2O6. 

This  body  has  been  found  in  the  iirine  of  dogs. 

Glyein.       (Glycocoll,   glycocin,   amido-acetic  acid.)       C2H5NO2,   or 

p-TT   /NH2 

This  is  one  of  that  important  class  of  compounds,  the  amido-acids, 
and  may  be  formed  in  the  laboratory  from  mono-chior-acetic  acid  and 
ammonia : 

CoH3C]02  +  2(NH3)  =  C2H2(NH2)0(OH)  +  NH4GI. 

It  is  peculiar  in  having  both  acid  and  basic  properties — i.  e.,  it  unites 
with  both  acids  a,nd  bases  to  form  crystallizable  compounds.  Glyein 
itself  may  be  obtained  in  crystalline  form  soluble  in  water.     Though 


APPENDIX.  689 

not  found  in  the  free  state  as  yet  in  the  body,  it  may  be  split  off  from 
bile  acids  and  hippuric  acid. 

Taurin.    CsHtNO.S,  or  C,H4;|^^. 

This  is  an  amido-isethionic  acid,  and  may  be  made  artiiacially  by  a 
laboratory  sj-nthesis,  as  well  as  derived  from  the  taurocholic  acid  of  the 
bile.  It  assumes  the  form  of  large  prisms,  soluble  in  water,  and  is  a 
remarkably  stable  compound.  Taurin  has  been  extracted  from  several 
organs  of  the  mammalian  body. 

Leucin.  C«Hi3N02  or  CH3,  CH=.CH2CHo.CH(NH.).C02H— i.  e.,  an 
amido-caproic  acid. 

This  compound,  which  may  be  obtained  from  the  pancreas,  spleen, 
thymus,  and  thyroid  bodies,  the  liver,  etc.,  and  occurs  as  a  x)roduct  of 
natural  and  artificial  pancreatic  digestion,  and  in  the  urine  in  acute 
atrophy  of  the  liver,  in  thin  whitish,  glistening,  flat  crystals,  soluble  in 
water.  Leucin  is  one  of  the  chief  products  of  the  decomposition  of 
nitrogenous  (proteid)  matter. 

Asparagin.     C4HeN203,  or  C.HalNHa)  ^Qj|^*-i.  e., 

Amido-succinamic  acid. 

Found  in  many  plants — as  asparagus,  licorice,  beets,  peas,  beans,  etc. 
— but  not  in  the  animal  body,  so  far  as  is  yet  known. 

Aspartic  acid  (or  Amido-succinic  acid). 
C«H7N04  or  C.H3(NH,)^^g=§. 

Found,  like  the  preceding,  most  abundantly  in  seeds,  but  said  also  to 
occur,  in  minute  quantity,  among  the  products  of  pancreatic  digestion. 

Glutaminic  acid.    C5H»N04. 

Seems  to  occur,  under  similar  natural  conditions,  to  those  giving  rise 
to  the  preceding  compound.  It  has  not,  however,  as  yet  been  shown  to 
ari.se  in  the  digestive  processes  of  animals. 

Cystin.    C3H,NS0,. 

By  some  chemists  this  compound  is  believed  to  be  an  amido-acid.  It 
appears  occasionally  in  tlie  urine,  but  is  chiefly  of  importance  as  making 
up  the  greater  part  of  certain  urinary  calculi  in  men,  dogs,  etc.  The 
l)ody  is  crystalline  :  insoluble  in  water,  alcohol,  and  ether,  but  soluble 
in  ammonia,  othor  alkalies,  and  the  mineral  acids. 

Acids  of  the  Benzine  or  Aromatic  Series. 

Benzoic  acid.    C«iH6.C0jiH. 

The  acid  itself  is  not  known  to  exist  in  the  body,  but  may  arise  in 
urine,  especially  that  of  the  herbivora,  from  fermentative  decomposi- 
tion : 

C.H.NO,  +  H,0  =  CH^NOq  -I-  0,11,0,. 

Hippuric  acid.  (ilycin.  Beii/ole  aclrl. 

Benzoic  acid  is  very  sparingly  soluble  in  water,  but  readily  dissolved 
by  alcohol  and  ethc;\ 
44 


690  ANIMAL  PHYSIOLOGY. 

Hippuric  acid  (Benzoyl-Glycin,  or  Benzoyl-amido  -  acetic  Acid) . 
C9H9NO3. 

This  acid  abounds  in  the  urine  of  the  herbivora,  being  derived,  proba- 
bly, from  some  benzoic  residue  in  the  food  (hay).  It  occurs  in  only 
small  quantity  in  the  urine  of  man.  It  may  be  obtained  in  prisms,  solu- 
ble in  boiling  water  and  in  alcohol. 

Phenol  (Carbolic  acid).     CeHe.OH. 

This  compound  occurs  under  the  same  circumstances  as  indol  in  the 
alimentary  tract,  and  may  be  extracted  from  the  faeces  and  the  urine. 
Slightly  soluble  in  water,  it  readily  dissolves  in  alcohol  and  ether. 

Tyrosin.    C9H11NO3. 

This  substance,  the  molecular  constitution  of  which  is  still  in  doubt, 
is  certainly  an  aromatic  body,  which  may  be  obtained  in  needles  ;  solu- 
ble in  hot  water,  acids,  and  alkalies,  but  insoluble  in  alcohol  and  ether, 

Tyrosin  occurs  with  leucin  in  the  decomposition  of  proteids,  and 
abundantly  in  the  natural  and  artificial  digestion  of  the  j)roteids,  by 
trypsin.  A  subslance  greatly  resembUng  it  has  been  made  artificially,  in 
the  laboratory,  by  a  synthesis. 


INDEX. 


Aberration,  chromatic.  573. 

spherical  of  the  lens,  572. 
Absorption  of  digested  food.  341. 

by  lymphatics,  341. 

by  skin,  418. 
Accelerator  nerves  of  heart,  270. 
Accommodation  of  eye,  505. 
Act  of  inspiration,  370. 
Acid  albumin,  073. 
Acids,  fatty  series,  080. 

acrylic  or  oleic  series,  081. 

glycolic  series,  082. 

oxalic  series,  083. 

bile  series,  084. 

benzine  or  aromatic  series,  089. 
Afferent  nerves,  482. 
Affections  of  retina,  482,  578. 
After-images,  589. 
Air,  entrance  to  and  exit  from  lungs,  369. 

quantity  respired,  378. 

inspired  and  expired,  comparison  of, 
381. 
Albumin,  native,  072. 

egg,  072. 

serum,  672. 

acid,  073. 

alkali,  073. 
Allantoin,  088. 
Allantoi.s,  75. 

Alteration  of  generations,  27. 
Amido-succinamic  acid,  089. 
Amnion,  74. 
Ama>V)a,  mi^rfihology  and  {)hvsi()l()gy  of. 

13,  13. 
Amylolytif:  action  of  saliva,  306. 
Amylopsin,  310. 
Anacrotic  pulse,  249. 
Anxmiu,  104. 


Animal  chemistry,  671, 

heat,  401. 

body,  27. 

kingdom,  classification  of,  33. 
Anode,  197. 

Anomalies  of  refraction,  574. 
Anterior  fasciculi,  488. 

radicular  zones,  488. 
Antero-median  columns,  488. 
Aphasia,  534. 
Apnoea,  398. 
Appendix. 
Area  pellucida,  07. 

opaca,  07, 
Arteries,  221. 
Asparagine,  689. 
Aspartic  acid,  089. 
I  Asphyxia,  respiration  and  circulation  in, 
I  404. 

pathological,  400. 
Astigmatism,  573. 
Auditory  ossicles,  607. 

impulses,  610. 

sensations,  015. 

perceptions.  015. 

judgments,  015 

discriminations,  016, 
Auricles  of  heart,  218. 
Automatism,  214. 
Axis  cylinder  of  nerve,  196. 

Bacteria,  18. 

Benzoic  acid,  089. 

Bile,  composition  of,  311. 

salts,  312. 

pigments,  312,  684. 

digestive  action  of,  313. 

comparative,  314. 


692 


ANIMAL   PHYSIOLOGY. 


Bile,  secretion  of,  333. 
Bilirubin,  684. 
Biliverdin,  685. 
Biology  general,  1. 
Blastoderm,  67. 
Blind-spot,  587. 
Blood,  147. 

comparative,  148. 
Blood-cells,  size  of,  149. 

varieties  of,  149. 

ratio  of  varieties  of,  150. 

history,  151. 

decline  and  death  of,  153. 
Blood,      morphological      elements 
149. 

chemical  composition  of,  154. 

quantity  and  distribution  of,  156. 

coagulation,  157. 

clinical  and  pathological,  163. 

summary  of  physiology  of,  165. 

supply,  influence  of,  200. 

circulation  of,  216-221. 

velocity  of,  224. 

pressure,  224-228. . 

quantity  of,  275. 

arterial,  383. 

venous,  383. 

carbon  dioxide  in,  389. 

vessels,  origin  of,  97. 
Brain,  498. 

circulation  in,  525. 
Broca's  convolution,  525. 
Bronchial  tubes,  structure  of,  368. 
Bulbus  arteriosus,  99. 
Burdaeh,  columns  of,  498. 

Capillaries,  281. 
Carbohydrates,  140,  678. 
Cardiac  movements,  232, 

sounds,  235. 

cycle,  240. 
Carnin,  688. 

Carbon  dioxide  in  blood,  389. 
Casein,  291,  673. 
Catelectrotonus,  197. 
Causes  of  heart-sounds,  236. 
Causation  of  heart-beat,  264. 
Caudate  nucleus,  536. 
Cell,  5. 
Cellulose,  7. 

Cerebro-cerebellar  fibers,  519, 
Cerebro-spinal  fibers,  519. 


of, 


Cerebral  cortex,  531. 

time,  535. 
Cerebro-spinal  and  system  of  nerves,  623. 

relations  of,  636. 
Cerebrum  general,  500. 

functions  of  its  convolutions,  505. 
Cerebellum,  functions  of  the,  541. 
Chemical  constitution  of  the  animal  body, 

135.  ' 
Chemical  changes  in  muscle,  192. 
Cheyne-Stokes  respiration,  398. 
Chitin,  678. 
Chlorophyl,  11. 
Choletelin,  685. 
Cholesterin,  684, 
Chondrin,  677. 
Chorion,  78. 

Chromatic  aberration,  573. 
Chronographs,  171. 
Chyle,  342. 
Cicatricula,  67. 
Cilia,  12. 
Ciliary  ganglion,  631. 

movements,  168. 
Circulation,  diagram  of,  224. 

under  the  microscope,  226. 

changes  in,  after  birth,  121. 

in  the  brain,  525. 

influenced  by  respiration,  400. 
Circulatory  and  respiratory  systems,  man, 

664. 
Classification  of  animal  kingdom,  33. 
Classification  and  distinguishing  charac- 
ters of  proteids,  138. 
Clinical  and  pathological,  blood,  163. 

re  nerve,  198. 

pulse,  251. 

saliva,  308. 

liver,  325. 

stomach,  336. 

vomiting,  339. 

lymph,  353. 

excretion,  354. 

digestion.  357. 

respiration,  379. 

asphyxia,  406. 

respiration,  408. 

glycogen,  435. 

fat,  445. 

heat,  467. 

vision,  603. 

hearing,  609. 


INDEX. 


693 


Clinical  and  Pathological,  taste,  G25. 

spinal  nerves,  637. 

cranial  nerves,  (329. 

voice,  646. 

speech.  651. 
Coagulation  of  the  blood,  157. 
Coitus,  121. 
Collateral  fibers,  519. 
Color-sensations,  583. 
Color-blindness,  585. 
Columns  of  Turck,  488. 

Burdach,  489. 

Gall,  489. 
Commissural  fibers  in  brain.  518. 
Comparative  re  blood,  148. 

heart's  pulsations,  243. 

pulse,  251. 

circulation,  253. 

capillaries,  281. 

digestion,  296,  319,  357. 

teeth,  304. 

saliva,  308. 

bile,  314. 

stomach,  330. 

swallowing,  335. 

vomiting.  339. 

movements  of  lymph,  343. 

respiration,  375. 

hiEmoglobin.  389. 

protective  function  of  skin,  313. 

respiration  by  skin,  415. 

kidney,  419. 

urine,  425. 

fat,  445. 

heat,  462. 

spinal  cord.  495. 

vision,  597. 

hearing,  616. 

smell,  622. 

taste,  626. 

voice  and  speech,  647. 

locomotion,  659. 

man,  668. 
Conjugation,  17. 

Constitution  of  animal  body,  137. 
Constitution,   chemical,    of    the   anirnai 

body,  135. 
Constituents  of  dead  muscle,  192. 
Contraction,  tetanic,  182. 

a  single  simfjie  muscular,  178. 

law  of.  198. 

of  i)U[)il  Cmyosis),  571. 


Contrast,  587. 
Co-ordination,  490. 

of  the  two  eyes  in  vision,  591. 
Corpuscles,  composition  of,  155. 
Corpus  luteuni,  113. 

striatum,  functions  of,  536. 
Corpora  quadrigemina,  functions  of,  539. 

striata,  518. 
Coughing,  406. 
Cranial  nerves,  628. 
Cramp,  205. 
Creatin,  197,  687. 
Creatinin,  446. 

Crura  cerebri,  functions  of,  541. 
Crusta,  538. 
Crying,  406. 
Curve,  the  muscle,  180. 
Cystin,  689. 

Death,  668. 
Decussation,  489. 
Defecation,  337. 
Deglutition,  332. 
Dentition,  665. 

Development,   physiological   aspects   <jf, 
112. 

post-embryonic,  of  blood-cells,  152. 
Dextrin,  679. 
Dextrose,  678. 
Diapedesis,  281, 
Diastole,  240. 
Diabetes,  artificial,  435. 
Dicrotic,  249. 

Dicidua  vera,  scrotina,  reflexa,  81. 
Diet,  452. 

fats  and  carbohydrates  in,  457. 

salts,  etc.,  in,  458. 

pathological,  459. 
Diflfusion-circles  565. 
Differentiation  of  unicellular  animals,  20. 
Digestion  of  food,  290. 

comparative,  296.  319,  357. 

pathological,  3571 

summary,  364. 
Digestive  juices,  306. 

action  of  bile,  313. 

organs,  self-digestion  of,  327. 
movements,  331. 
evolution,  363. 

system,  man,  6(J4. 
Dilation  (mydriasis),  572. 
Dioptrics  of  vision,  563, 


694 


ANIMAL   PHYSIOLOGY. 


Direct  observation,  method  of,  141. 

cerebellar  tracts,  488. 
Discus  proligerus,  58. 
Divisions  of  food-stuffs,  390. 
Dreaming,  527. 
Ductus  venosus,  104. 
DyspncBa,  397. 

Ectoplasm,  7. 

Efferent  nerves,  482. 

Elasticity  of  muscle,  187. 

Elastin,  677. 

Electrical  phenomena  of  muscle,  188. 

organs,  199. 
Electrodes  non-poiarizable,  189. 
Electrotonus,  197. 
Embryo,  54. 

development  of,  90. 
Embryological,  alimentary  tract,  295. 

nervous  system,  542. 

vision,  562. 
Endoplasm,  7. 
End-plates,  nerve,  170. 
End-bulbs  of  Krause,  549. 
Energy  of  the  animal  body,  459. 
Entoptic  phenomena,  574. 
Epiblast,  93. 
Estimation  of  the  size  and  distance  of 

objects,  595. 
Eustachian  tube,  609. 
Evolution  of  vascular  system,  285. 

digestive  organs,  363. 

respiratory  organs,  409. 

uric  acid,  448. 

digestion,  468. 

spinal  cord,  496, 

nervous  system,  543. 

evidences  of,  43. 

placenta,  89. 

organic,  reconsidered,  127. 

vision,  600. 

voice  and  speech,  652. 

locomotion,  662. 

hearing,  616. 
Excretion  of  perspiration,  416. 

by  kidney,  419. 

pathological,  354. 
Experimental,  reflex  action,  212. 
Expulsion  of  urine,  429. 
Extractives  of  muscle,  194. 
Eye,  optical  imperfections  of,  572. 

protective  mechanisms,. 596. 


Fjeces,  353. 
Fallopian  tube,  114. 
Fatigue,  200. 
Fats,  the,  139. 

peculiar,  140. 

in  milk,  292. 
Fat,  the  construction  of,  440. 

formation  of,  441. 

pathological,  445. 

comparative,  445. 
Feeding  experiments,  454. 
Ferments,  unorganized,  160. 
Fibrin,  675. 
Fibrin-ferment,  160. 
Fibrinogen,  159,  674. 
Fission,  11. 

Foetal  circulation,  103-118. 
Food,  digestion  of,  290. 

special  considerations,  358. 
Food-stuff's,  divisions  of,  290. 
Forced  movements,  504. 
Formic  acid,  680. 
Frog,  the  rheoscopic,  191. 
Fungi,  15. 

Qanglia,  cardiac,  273. 
G-anglion,  ciliary,  otic,  etc.,  631. 
Gas-pump,  mercurial  (Ludwig's),  384. 
Gases,  foreign  in  respiration,  392. 
Gastric  juice,  308. 

characters  of,  309. 
Gastrula,  the,  66. 
Gelatine,  677. 
Gelatine  in  diet,  457. 
Gemmation,  11. 
Germinal  vesicle,  54, 

spot,  54. 

ridge,  57. 
Globin,  674. 
Globulins,  674. 
Glomerulus,  42. 
Glycin,  688. 
Glycocholic  acid,  313. 
Glycocoll  (glycin),  312. 
Glycogen,  432,  679. 

uses  of,  434. 

pathological,  435. 
Glutaminic  acid,  689. 
GoU,  columns  of,  489. 
Goltz,  experiments  of,  523. 
Graafian  follicles,  57. 
Gray  matter  of  cerebram,  512. 


INDEX. 


695 


Graphic  method,  applications  of,  171. 
Growth  at  different  periods,  668. 
Guanin,  688. 

Habit,  the  law  of,  40. 
H.-ematoblasts.  149. 
Ha?matin.  389. 
Haemin,  389. 
Haemoglobin,  385 

comparative,  389. 
Hearing,  604. 
Heart,  the  mammalian;  217,  232. 

the  action  of,  223. 

impulco,  233. 

sounds,  causes  of,  236. 

work,  241. 

nervous  system  in  relation  to,  261. 

beat,  causation  of,  270. 

accelerator,  nen'es  of,  385. 
Heat,  animal,  461. 

comparative,  462. 

production  of,  465. 

pathological,  467. 
Heat-producing  power  of  foods,  460. 
Hermaphroditism.  25. 
Hibernation,  465,  470,  527. 
Hiccough,  407. 
Hippuric  acid,  449. 
Holoblastic,  70. 
Homoiothermer,  465. 
Horopter,  the,  594. 
Hyphae,  15. 
Hypernoea,  397. 
Hydra.  22. 
Hydrobilirubin,  685. 
Hypnoti-sm,  528. 
Hypoblast,  69,  93. 
Hypoxanthin,  688. 

Imperfections  of  visual  perceptions,  587. 

Impulse  of  the  heart,  233. 

Impulses,  path  of,  in  spinal  cord,  491. 

Indican,  685. 

Indigo  series,  685. 

Iiidol,  31.3,  686. 

Inductorium,  Du  IJois-Reymond's,  175. 

Influence  of  jiigment   of  macula  lutea, 

5S9. 
Infusfjria,  22. 
Inhibition,  venous,  215. 

of  reflexes,  485. 
Inosit,  079. 


Intercerebral  fibers,  518. 

Internal  capsule,  536. 

Intestinal  movements,  337. 

Inspiration,  act  of,  370. 

Irradiation,  587. 

Irritability  of  muscle  and  nerve,  169. 

Juice,  gastric,  308. 

pancreatic,  315. 
Juices,  the  digestive,  306. 

characteristics  of,  307. 

Karyokinesis,  6,  65. 

Katacrotic  pulse,  249. 

Kathode.  197. 

Keratin,  678. 

Kidney,  excretion  by,  419. 

comparative,  419. 
Kymograph,  231. 
Kynurenic  acid,  688. 

Latent  period,  181. 
Lardacein,  677. 
Laughing,  406. 
Law  of  contraction,  198. 

rhythm,  206. 
Lecithin,  683. 
Lenticular  nucleus,  536. 
Leucin,  316. 
Leucocytes,  150. 
Liquor  aranii,  74. 

sanguinis,  150. 
Liver,  metabolism  of,  490. 
Localization,  in  cerebral  cortex,  523,  530. 
Locomotion,  655. 
Locomotor  ataxia,  490. 
Lymph,  342. 

movements  of,  comparative,  343. 
Lymphatics,  absorption  of  food  by,  341. 

Macula  lutea,  influence  of  pigment  of, 

589. 
Malpighian  tubules,  421. 
Maltose,  679. 
Man  at  dilTerent  periods  of  his  existence, 

663. 
Man's  place  in  the  aniiiuil  kingdom,  35. 
Maturity  (puberty),  666. 
Mastication,  3.32. 
Maximal  stimulus,  185. 
Medulla  oblongata.  542. 
Membrana  tympani,  600. 


696 


ANIMAL   PHYSIOLOGY. 


Membranes,  embryonic,  of  birds,  72. 

foetal  of  mammal,  76. 
Menstruation,  113. 
Meroblastic,  70. 
Mesoblast,  93. 
Mesonephros,  106. 
Metanephros,  106. 
Metabolism,  the.  of  the  body,  431. 

of  the  liver,  432. 

of  the  spleen,  436. 

in  formation  of  urea,  uric  acid,  hippu- 
ric  acid,  etc.,  446. 

proteid,  455. 

influence  of  nervous  system  on,  471. 

summary  of,  476. 
Metazoa,  5. 
Methfemoglobin,  389. 
Micturition.  430. 

pathological,  430. 
Middle  ear,  muscles  of,  608. 
Milk,  proteids  of,  291. 

fats,  292. 

sugar  of,  292,  679. 

salts,  292. 
Minimal  stimulus,  185. 
Misconceptions  as  to  comparative  size, 

etc.,  of  objects,  590. 
Moist  chamber,  176. 
Morphology,  definition  of,  1. 
Motor  area,  525. 
Movements,  cardiac,  232. 

ciliary,  168. 

stomach,  335. 

intestinal,  337. 

digestive  organs,  331. 

ocular,  592. 
Mucin,  327,  677. 
Mucor  mucedo,  15. 
Mucigen,  327. 
Miillerian  duct,  108. 
Multicellular  organism,  22. 
Munk,  experiments  of,  524. 
Muscle,  167. 

irritability  of,  169. 

curve,  180. 

changes  in,  during  contraction,  186. 

elasticity  of,  187. 

electrical  phenomena  of.  188. 

electrical  currents  in,  190. 

chemical  changes  in,  192. 

dead,  constituents  of,  194. 

thermal  changes  in  contracting,  195. 


Muscle,  unstriped,  204. 

comparative,  205. 
Muscles  of  respiration,  372. 

of  middle  ear,  608. 
Muscular  note,  184. 

work,  199. 

sense,  557. 

energy,  sources  of,  461. 
Mydriasis,  572. 
Myosis,  571. 

Myograph,  pendulum,  179. 
Myosin,  193,  674.  ■ 

Nerve-supply,  643. 

Nerves,  the  physiology  of,  197. 

clinical  and  pathological,  198. 

irritability  of,  169. 

afferent  and  efferent,  482. 

cerebro-spinal,  626. 

third,  fourth,  etc.,  628,  629. 
Nervous  system,  210. 

in  relation  to  the  heart,  261. 

relation  to  respiration,  393. 

man,  666. 
Nervous  supply,  muscles  of  mastication, 

332. 
Nervous  mechanism  in  the  sexual  act, 

124. 
Neurin,  683. 
Neuralgia,  517. 
Neutral  fats,  681. 
Nitrogenous  metabolites,  140,  686. 

equilibrium,  456. 

fats,  complex,  683. 
Non-crystalline  bodies,  677. 
Non-crystalline  bodies,  certain,  138. 
Non-nitrogenous  metabolites,  141. 
Note,  the  muscular,  184. 
Nucleus,  5. 
Nucleolus,  5. 
Nuelein,  678. 

Objects,  estimation  of  size  and  distance, 

590. 
Observation,  direct  method  of,  141. 

graphic  method  of,  143. 

summary  of  methods  of,  147. 
Ocular  movements,  592. 
Old  age,  667. 
Oligsemia.  164. 
Oncograph,  438. 
Oosperm,  the,  62. 


INDEX. 


097 


Optic  thalami,  518. 

Optic  thalamus,  functions  of,  536. 

Optical  imperft'ctions  of  the  eye,  572. 

Organic  evolution,  41. 

Organs,  electrical,  199. 

Origin,  the,  of  the  germs  of  life,  41. 

Ovary,  origin  of,  110. 

Ovulation,  115. 

Ovum,  the,  54. 

origin  and  development  of,  57. 

changes  in,  59. 

fertilization  of,  62. 

nutrition  of,  115. 
Oxyhsemoglobin,  386. 

Pacinian  corpuscles,  553. 

Pancreatic  juice,  315. 

Physiology  of  secretion,  323. 

Paraglobulin,  159,  674. 

Parthenogenesis,  53. 

Parturition.  120. 

Patellar  reflex,  494. 

Path  of  impulses  in  spinal  cord,  491. 

Peduncles  of  the  brain,  537. 

Pepsin,  311. 

Peptone,  310,  315. 

Peptones,  075. 

Perspiration,  excretion  of,  416. 

Pettenkofer's  test,  684. 

Phenol,  690. 

Physiology  of  secretion,  319. 

sweating,  417. 
Pigments  of  urine,  685. 
Placenta,  80. 

the  discoidal  and  raeta-discoidal,  81. 

th6  zonary,  diffuse,  polycotvledonarv, 
80. 

evolution  of,  89. 
Poikilothormer,  405. 
Polar  colls  of  globules,  59. 
Polyps,  22. 
Pons  Varolii,  518. 

functions  of.  541. 
Predicrotic,  249. 
Pressure  sensations,  554. 
Pressures,  endocardial,  238. 
Primitive  streak,  71. 

groove,  71. 
Pro-amnion,  78. 
Production  of  heat,  4;]5. 
Pronephros,  95. 
Pronucleus,  feinule,  00. 


Protagon,  683. 

Protective  mechanism  of  the  eye,  596. 

Proteid  metabolism,  455. 

Proteids,  671. 

properties  and  classification  of  the,  672. 

general  charactei-istics  of,  138. 

classification  and  distinguishing  char- 
acters of,  138. 

of  milk,  291. 

metabolism,  455. 

tests  for,  673. 

coagulated,  675. 
Protococcus,  morphology  and  physiologv 

of,  11,  12. 
Protoplasm,  2,  27. 
Protovertebrae,  95. 
Psychological  aspects  of  vision,  586. 
Pulse,  the,  244. 

venous,  251. 
Pupil,  alterations  in  the  size  of  the,  569. 

Quantity  of  air  respired,  378. 

Reaction  time,  536. 
Reduced  reaction  time,  536. 
Reflex  action,  211. 

functions  of  spinal  cord,  484. 

time,  486. 
Reflexes,  inhibition  of,  485. 
Refraction,  anomalies  of,  574. 
Regulation  of  temperature,  464. 
Regurgitation,  340. 
Reproduction,  50. 
Research  and   reasoning,   physiological, 

141. 
Respiratory  system,  365. 

sounds,  379. 
Respiration,  muscles  of,  372. 

types  of,  373. 

comparative,  375. 

pathological,  379. 

in  the  blood,  383. 

in  the  tissues,  392. 

relation  of  nervous  system  to,  393. 

influence  of  condition  of  blood  in,  oUl. 

Cheyne-Stokes,  398. 

effects  of  variations    in    atmospheric 
pressure,  399. 

influence  on  circulation,  400. 

clinical  and  f)athological,  408. 

evolution,  409. 
liesting  stage  of  ovum,  05. 


698 


ANIMAL   PHYSIOLOGY. 


Rhythm,  law  of,  206. 

in  nature,  36. 

appetite,  362. 

respiratory,  379. 
Retina,  affections  of,  578. 
Retinal  stimulation,  laws  of,  580. 
Rigor  mortis,  192. 
Rheoscopic  frog,  191. 
Rouleaux  of  blood-cells,  158. 

Saliva,  306. 

amylolytic  action  of,  306. 

of  parotid  gland,  307. 

comparative,  308. 

pathological,  308. 
Salivary  glands,  physiology  of  secretion 

of,  319. 
Salts  of  milk,  292. 
Sareolemma,  170. 
Secretion,  physiology  of,  319. 

nature  of  the  act  of,  326. 

of  urine,  426. 
Segmentation  of  ovum,  65. 
Segregation,  130. 

Self-digestion  of  digestive  organs,  329. 
Semicircular  canals,  co-ordinating  func- 
tions of,  502. 
Sensations,  visual,  576. 
Senses,  general  remarks,  548. 
Sensory  area,  525. 
Serum,  composition  of,  155. 
Sexes  at  different  periods,  667. 
Sexual  selection,  42. 
Sighing,  407. 
Skatol,  686. 
Skin,  functions  of,  412. 

protective   functions  of,  comparative, 
413. 

respiration  by,  comparative,  415. 

absorption  by,  418. 

as  an  organ  of  sense,  451. 
Sleep,  526. 
Smell,  sense  of,  620. 
Sneezing,  407. 
Sobbing,  406. 
Solidity  in  vision,  595. 
Somatopleure,  74. 
Somnambulism,  529. 
Sound,  cardiac,  Marey's,  234. 
Sounds,  cardiac,  235. 

respiratory,  381. 
Special  considerations  as  to  food,  358. 


Special  considerations  as  to  digestion,  468. 

vision,  597. 

hearing,  616. 

voice  and  speech,  652. 
Spectrum  of  haemoglobin,  386. 
Spermatozoon,  52. 

origin  of,  61. 
Speech,  649. 

consonants,  650. 
Spherical  aberration,  572. 
Sphygmograph,  the,  247. 
Spinal  nerves,  626. 

cord,  480. 
reflex  functions  of,  484. 
as  a  conductor  of  impulses,  487. 
automatic  functions  of,  493. 
comparative,  495. 
evolution,  496. 
Splanchnopleure,  74. 
Sporangia,  15. 
Spleen,  metabolism  of,  436. 

nervous  system's  influence  on,  439. 

pulp,  comparative,  437. 
Stasis,  281. 

Starvation,  influence  on  metabolism,  450. 
Steapsin,  316. 

Stimulation,  laws  of  retinal,  581. 
Stimulus,  170. 

maximal,  185. 

minimal,  185. 

sub-maximal,  185. 
Stomach  of  ruminants,  300. 

physiology  of  secretion  by,  323. 

comparative,  330. 

movements  of,  335. 
Subjective  phenomena,  591. 
Succus  entericus,  317. 
Summary  of  physiology  of  blood,  165. 

muscle  and  nerve,  208. 

circulation,  286. 

digestion,  355-364. 

respiration,  410. 

functions  of  the  skin,  418. 

urine,  430. 

reproduction,  89. 

voice  and  speech,  652. 

spinal  cord,  497. 

functions  of  the  brain,  548. 

of  evidences  of  evolution.  47. 
Swallowing,  compai'ative,  334,  335. 
Sweating,  415. 

physiology  of,  417. 


INDEX. 


699 


Synopsis,  brief,  of  physiology  of  vision, 
602. 
physiology  of  hearing,  620. 
Systole,  340. 

Tactile  sensibility,  555. 

Tambour  of  Marey,  177. 

Taste,  sense  of,  623. 

Taurin,  312. 

Tauroeholic  acid,  313. 

Teeth,  comparative,  304. 

Tegmentum.  538. 

Temperature,  influence  of,  on  muscle,  203. 

regulation  of,  464. 
Testes,  61. 

Tests  for  proteids,"  672. 
Tetanic  contraction,  183. 
Thermal  changes  in  contracting  muscle. 
195. 

sensations,  554. 
Thoracic  breathing,  373. 
Time,  cerebral,  535. 
Tissues,  the  contractile,  166. 

respiration  in,  393. 

comparative,  167. 
Traube-Hering  curves,  403. 
Trypsin,  316. 
Tunicin,  680. 
Tiirck,  columns  of,  488. 
Types  of  respiration,  373. 
Tyrosin.  316. 

U^nicellular  animals,  20. 
Umbilical  vesicle,  73. 
Urea,  424,  686. 

and  uric  acid,  metabolism,  in  forma- 
tion of,  446. 

nitrate,  687. 
Uric  acid,  448. 

evolution,  448. 
Urine,    chemically    and    physiologically 
considered.  422. 

quantity,  433. 

constituents  of,  423. 

.•«alts  of,  434. 

abnormal,  425. 

com  parative,  435. 

s<jcretion  of,  486.  I 

expulsion  of,  429. 

pigments  of,  685. 
Urobilin,  685. 
UrfMjrythrin,  685. 


Urogenital  system,  development  of,  106. 
Uses  of  glycogen,  434. 

Vagus,  influence  on  the  heart,  265. 
Valves  of  the  heart,  219. 
Valvulfe  conniventes,  357. 
■Variations,  functional,  in  muscle,  207. 

of  cardiac  pulsation,  242. 
Vascular  system,  evolution  of  the,  285. 

development  of  the,  103. 
Vaso-motor  influences,  277. 
Vas  deferens,  origin  of,  110. 
Veins,  221. 

valves  of,  222. 
Velocity,  the,  of  the  blood,  224. 

of  nervous  impulse,  measurement  of, 
181. 
Venous  pulse,  251. 
Ventricles,  of  the  heart,  218. 
Vision,  559. 

embryological,  562. 

dioptrics  of,  563. 

psychological  aspect  of,  583. 

synopsis  of  physiology  of,  602. 

astigmatic,  573. 

spherical  aberration  of,  572. 

chromatic  aberration  of,  573. 

entoptic  phenomena  of,  574. 

anomalies  of  refraction  of,  574. 

sensations  of,  576. 

affections  of  the  retina  in,  578. 

psychological  aspects  of,  586. 

co-ordination  of  the  two  eyes  in,  591. 

estimation  of  solidity  by,  595. 
Visual  sensations,  576. 

impulses,  nature  of,  580. 

angle,  582. 

perceptions,  imperfections  of,  587. 
Vitellin,  674. 
Vitelline  membrane,  55. 
Voice  and  speech,  639. 

registers  and  falsetto,  644. 

pathological,  646. 

comparative,  647. 

evolution,  653. 

summary,  653. 
Vomiting,  comparative,  338,  339. 

pathological,  339. 

Wolflian  duct,  98,  100. 

bodies,  100. 
Work,  muscular.  1!»9. 

of  the  heart.  341. 


TOO 


ANIMAL   PHYSIOLOGY. 


Xanthin,  194, 

Yawning,  407. 

Yeast,  morphology,  chemistry,  and  physi- 
ology of,  9,  10. 


Zona  radiata,  55. 
Zoogloea,  18. 
Zygospore,  17. 
Zymogen,  328. 


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3 

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BURT  (STEPHEN  SMITH).  Exploration  of  the  Chest  in  Health  and  Disease. 
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CAMPBELL  (F.  R.).  The  Language  of  Medicine.  A  Manual  giving  the  Origin, 
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Conditions.     12mo.     Cloth,  $3.00. 

CARTER  (ALFRED  H.).  Elements  of  Practical  Medicine.  Third  edition,  re- 
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STRECKER  (ADOLPH).  Short  Text- Book  of  Organic  Chemistry.  By  Dr. 
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W.  H.  Ilodgkinson  and  A.  J.  Greeiiaway.     8vo.     Cloth,  $5.00. 

STRtMPELL  (ADOLPH).  A  Text-Book  of  Medicine,  for  Students  and  Prac- 
titioners.    With  111  Illustrations.     Svo.     Cloth,  $6.00;  sheep,  $7.00. 

SWANZY  (HENRY  R.).  A  Hand-Book  of  the  Diseases  of  the  Eye,  and  their 
Treatment.  With  122  Illustrations,  and  Holmgren's  Te.sts  for  Color-Blind- 
ness.     Crown  Svo.     Cloth,  $3.00. 

TRACY  (ROGER  S.).  The  Essentials  of  Anatomy,  Physiology,  and  Hygiene. 
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and  20,  1884.     Small  Hvo.     Cloth,  $5.00. 

TYNDALL  (JOHN).  Essays  on  the  Floating  Matter  of  the  Air,  in  lielation  to 
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Second  edition,  revised  and  enlarged.     8vo.     Cloth,  $3.00;  sheep,  $4.00. 

VAN  BUREN  (W.  H.).  Lectures  on  the  Principles  and  Practice  of  Surgery. 
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son,  M.  D.     8vo.     Cloth,  $4.00 ;  sheep,  $5.00. 

VOGEL  (A.).  A  Practical  Treatise  on  the  Diseases  of  Children.  Translated 
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tion, revised  and  enlarged.  Illustrated  by  six  Lithographic  Plates.  8vo. 
Cloth,  $4.50  ;  sheep,  $5.50. 

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ian von  Zeissl.  Authorized  edition.  Translated,  with  Notes,  by  H.  Ra- 
phael, M.  D.     8vo.     Cloth,  $4.00;  sheep,  $5.00. 

WAGNER  (RUDOLF).  Hand- Book  of  Chemical  Technology.  Translated  aud 
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Crookes.     With  336  Illustrations.     8vo.     Cloth,  $5.00. 

WALTON  (GEORGE  E.).  Mineral  Springs  of  the  United  States  and  Canadas. 
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etc.     Second  edition,  revised  and  enlarged.     12mo.     Cloth,  $2.00. 

WEBBER  (S.  G.).  A  Treatise  on  Nervous  Diseases :  Their  Symptoms  and 
Treatment.    A  Text-Book  for  Students  and  Practitioners.   8vo.   Cloth,  $3.00. 

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Questions  for  Review  and  Examination,  and  Vocabulary  of  Medical  Terms. 
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WELLS  (T.  SPENCER).    Diseases  of  the  Ovaries.     8vo.     Cloth,  $4.50. 

WYETH  (.JOHN  A.).  A  Text-Book  on  Surgery :  General,  Operative,  and  Me- 
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WYLIE  (WILLIAM  G.).  Hospitals:  Their  History,  Organization,  and  Con- 
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